Download Specific Bacteriology Learning Objectives

Specific Bacteriology Learning Objectives
(referenced to Murray’s textbook where relevant)
1. Bacterial Structure, Physiology & Classification
(Chapters 2, 3, 4; Dr. Yother’s outline)
A. Compare and contrast the properties of eukaryotes vs. prokaryotes. (p. 11, Fig.
3.1)
Eukaryotes
Prokaryotes
Animal, plant and fungi
Bacteria and blue green algae
True nucleus
Primitive nucleus
80s ribosome
70s ribosome
DNA diploid strands
Single circular haploid DNA
Have organelles
Lack nucleus and organelles
Extrachromosomal DNA in organelles
Extrachormosomal DNA in plasmids
No cell wall (except fungi)
Peptidoglycan cell wall (most)
Sexual and asexual reproduction
Asexual/binary fission
Respiration via mitochrondria
Respiration via cytoplasmic membrane
Sterols usually present
Sterols absent
B. Compare and contrast cell wall components in gram-positive vs. gramnegative bacteria. (p. 12-24)
Gram Positive: thick peptidoglycan layer containing wall teichoic acid
(WTA) covalently linked to peptidoglycan and lipoteichoic acids (LTA)
membrane anchored, not covalently linked
Gram Negative: thin peptidoglycan layer, outer membrane containing
lipopolysaccharide, phospholipids, and proteins. Periplasmic space
between cytoplasmic and outer mem contains transport, degradative and
cell wall synthetic proteins. Outer mem is joined to the cytoplasmic mem
at adhesion points and is attached to peptidoglycan by lipoprotein links.
C. Understand structure and function of each bacterial major ultrastructural
component: chromosome, plasmid, ribosome, inner (cytoplasmic) membrane,
outer membrane, mesosome, teichoic acid, peptidoglycan, lipopolysaccharide,
capsule, pili, flagella, endospores. (p.12-22).
Chromosome: single (haploid) double stranded circle not contained in
nucleus but discrete area called nucleoid, no histones, no nucleosomes,
600-4500kb, ~1kb/gene
Plasmid: smaller, circular extrachromosomal DNAs, usually in gram
negative, usually not essential: provide selective advantage (antibiotic
resistance, metabolic, virulence, conjugative), few to several hundred kb
Ribosome: 30s + 50s subunits, form 70s ribosome, translation of mRNA to
protein
Cytoplasmic membrane: lipid bilayer structure, NO STERIODS (except
mycoplasmas), responsible for electron transport, energy production,
transport of metabolites, ion pumps and enzymes, photosynthesis,
affected by antibacterials, detergents, polymyxins, ionophores
Outer membrane: unique to gram-negative, stiff, maintains bacterial
structure and is a permeability barrier to large molecules (>800Da) and
hydrophobic molecules; asymmetric bilayer: inner phospholipids, outer
LPS, proteins include transport and porins
Mesosome: coiled cytoplasmic membrane, acts as an anchor to bind and
pull apart daughter chromasome during cell division
Teichoic acid: water soluble, anionic polymers of polyol phosphates,
covalently linked to peptidoglycan and essential to cell viability, important
in virulence, shed into media and host, can initiate host responses similar
to endotoxin (gram +)
Lipoteichoic acid: fatty acid and anchored in the cytoplasmic membrane,
common surface antigens (gram +)
Peptidoglycan: (murein) rigid layers surrounding cytoplasmic membrane,
helps determine cell shape, NaG/NaM crosslinked
LPS: amphiphatic (hydrophobic/philic ends) molecule, composes outer
leaflet of outer membrane, ENDOTOXIN, activates B cells, release of IL-1,
IL-6, TNF, causes fever and shock, shed into media and host, (gram -),
structure: Lipid A---core polysaccharide-O Ag; polysaccharide varies with
strain, 3-4 sugars/repeat up to 25 repeats, used for serotyping
Capsule: loose polysaccharide or protein layer surrounding bacteria, also
slime layer or glycocalyx, poorly antigenic and antiphagocytic, major
virulence vactor, acts as a barrier and promotes adhesion to other bacteria
and host tissue surfaces
Pili: fimbriae, hairlike structures on the outside of bacteria; composed of
pilin protein subunits, smaller in diameter, not coiled, usually arranged
uniformly over entire surface, promote adherence, F pili or sex pili bind
other bacteria and transfer chromosomes between, encoded by F plasmid
Flagella: ropelike propellers composed of helically coiled protein subunits
of flagellin, anchored in membranes through hook and basal body
structures, driven by membrane potential. Provide motility, chemotaxis
(swim and tumble); peritrichous-all around, polar-one end, bipolar-both
ends
Endospores: formed by gram POSITIVE, under harsh environmental
conditions, convert from vegetative to dormant state, a dehydrated
multishelled structure that protects and allows bacteria to exist in
“suspended animation”, clostridium, bacillus
D. Describe the procedure for Gram-stain and explain the purpose of each
reagent. (p.12)
Heat fix/dry to slide
Stain with crystal violet (adheres to peptidoglycan), which is precipitated
with iodine (acts as mordant by increasing the affinity of the dye for the
cell)
Unbound/excess stain removed with 95% alcohol/acetone-based
decolorizer and water
Red counterstain safranin added to stain decolorized cells
Gram +: turn purple, stain trapped in thick peptidoglycan
Gram -: thin peptidoglycan does not retain crystal violet, turn red
E. Explain the structural differences of the mycobacterial cell wall from other
bacteria that cause it to be “acidfast. (p. 18)
Mycobacteria have peptidoglycan layer with a slightly different structure,
which is intertwined with and covalently attached to an arabinogalactan
polymer and surrounded by a waxlike lipid coat of mycolic acid (fatty
acids), cord factor (glycolipid), waxD (glycolipid) and sulfolipids, which
causes them to be “acid fast”. Responsible for virulence and is
antiphagocytic.
F. Explain the process by which peptidoglycan is synthesized. (p. 18-19)
1. Synthesized from prefabricated units constructed and activated for
assembly and transport inside the cell. Glucosamine converted to MurNAc,
activated.
2. At the membrane the units are attached to the bactoprenol
(undecaprenol phosphate) conveyor belt and fabrication is completed.
GlcNAc is added.
3. Unit is translocated to the outside, GlcNAc-MurNAc is attached to
polysaccharide chain via transglycosylases.
4. Near membrane surface peptide is cross-linked via peptide bond
exchange (transpeptidation) between free amine of amino acid in third
position (lysine) and d-ala at fourth position, releasing terminal d-ala of
precursor. Transpeptidases and carboxypeptidases catalyze reactions;
these are penicillin-binding proteins (PBPs), targets for β-lactam
antibiotics.
G. Explain the process and purpose of spore formation and name the two main
genera of bacterial pathogens that produce spores. (p. 22-24)
-Depletion of nutrients triggers cascade: spore mRNA transcribed, other
mRNA turned off. Dipicolinic acid produced, antibiotic and toxins are
excreted. Chrom duplicated, one copy of DNA and cytoplasmic contents
(core) surrounded by cytoplasmic mem, peptidoglycan and mem of
septum. Two layers of mem and pep surrounded by the cortex, made of
thin inner peptidoglylycan surrounding what used to be cytoplasmic mem,
and loose outer pep layer. Cortex is surrounded by touch, keratin-like
protein coat for protection.
-Spore contains a complete copy of the chromosome, the bare minimum
conc of essential prot and ribosomes, and a high conc of Ca bound to
dipicolinic acid. It protects the genomic DNA from intense heat, radiation
and attack by enzymes and chemical agents.
-Bacillus (anthrax) and clostridium (tetanus and botulinum)
H. Describe how mycoplasmas are unique from other bacteria and how these
differences are responsible for their morphology and life cycle. (p. 18)
Mycoplasmas have no peptidoglycan cell wall and incorporate steroids
from the host into their membrane.
I. Explain how the presence of a capsule is important as a bacterial virulence
factor and provide examples of clinically important bacteria that are encapsulated.
(p. 17)
Capsules are unnecessary for growth of bacteria but important for survival
in the host. It’s poorly antigenic and antiphagocytic, and is a major
virulence factor. It blocks C3b deposition, if complement does attach it
blocks phagocyte receptor binding. It acts as a barrier to toxic hydrophobic
molecules, and promotes adherence. Streptococcus mutans’ capsule
allows attachment to tooth enamel. Bacillus anthracis produces a
polypeptide capsule, Streptococcus pneumoniae’s capsule acts as a
major virulence factor.
J. Understand the processes of DNA replication, mRNA transcription and
translation and the steps involved in each. (p. 30-31)
DNA replication: synthesized semiconservatively by DNA polymerase,
using both strands, occurs at growing forks, proceeds bidirectionally.
Leading strand synthesized continuously 5’-3’, lagging strand synthesized
in okazaki fragments using RNA primers 5’-3’. DNA polymerases
proofread, completes when forks meet 180 degrees from origin,
topoisomerases release strain.
Transcription: via DNA-dependent RNA pol, sigma factor binds
promoter sequence and provides a docking site for RNA pol. Once
bound, RNA synthesis proceeds with addition of ribonucleotides
complementary to the sequence in DNA. Once gene or operon has been
transcribed, RNA pol dissociates, produces mRNA.
Translation: mRNA converted to protein; 3 nucleotides form codon,
encodes a particular aa. tRNA contains anticodon, allows base pairing.
Begins when ribosome binds start codon (AUG), contains A (aminoacyl)
and P (peptidyl) sites for basepairing. tRNA matching second codon binds
A site, aa forms peptide bond with aa in P site via transpeptidation, leaves
tRNA in P site uncharged and is released. The ribosome moves down,
transferring tRNA to P site, leaving A site for next tRNA. Continues until
reaches termination codon.
K. Describe the events that occur in each phase of bacterial growth. (p. 33, Fig.
4-11)
When first added to new medium, bacteria require time to adapt to new
environment, known as lag phase. Bacteria are actively metabolizing and
preparing for active growth. During log or exponential phase, bacteria
grow and divide with a doubling time characteristic of strain/conditions.
When the culture runs out of metabolites or toxic substance builds up,
metabolic activity and growth slows/stops and bacteria enter stationary
phase. Finally, death phase occurs, an exponential decline and loss of
viability.
L. Explain the difference between oxidation and fermentation and give examples
of bacteria which are “fermenters”, “oxidizers” or “asaccharolytics”. (p. 28-29; lab
syllabus)
Oxidation converts pyruvic acid to water and CO2 via the TCA cycle in
the presence of oxygen. This allows the organism to generate 3 moles of
ATP/NADH, and 2 moles of ATP/FADH2, and 38 ATP/glucose. Carried
out by obligate aerobes and facultative anaerobes.
“Oxidizers”: Staphylococcus, Enterococcus, Neisseria, Helicobacter,
Fermentation converts pyruvic acid to various end products in the
absence of oxygen. Organic molecules, rather than oxygen, are used as
electron acceptors to recycle the NADH produced during glycolysis. This
produces 2 ATP/glucose. An anaerobic process carried out by obligate
and facultative anaerobes.
“Fermenters”: Streptococcus, Lactobacillus, enteric bacteria (E. coli,
Salmonella), Clostridium.
“Asaccharolytics”: use substrates other than sugars for metabolic energy,
unable to oxidize/ferment carbs; Campylobacter, B. pertussis, L.
pneumonphila
M. Explain the importance of determining genetic relatedness of bacteria in
epidemiology and infection control. (lecture outline)
Serological classifications become important in epidemiology. Bacteria are
examined to determine what isolates are causing the most disease. For
example, the Streptococcus pneumoniae (causes pneumonia) vaccine is
directed against the polysaccharide capsule. There are more than 90
different serological capsules that that bacterium can produce. When
vaccines are being developed, it is important to know that those vaccines
are directed to that capsule. It is also important to know what serotypes
are actually most encountered in disease because those are the ones that
we want to use in making our vaccine and antiserum to that capsule. In
serological classification, you are usually looking at surface antigenscapsules, O Ag (LPS), flagella, polysaccharides, proteins, and pili. Not as
important in trying to identify an isolate, but important in epidemiology.
N. Explain the differences, advantages, and disadvantages among phenotypic,
analytic, and genotypic classification of bacteria and provide examples of each
approach. (p. 8;lecture outline)
Phenotypic classification: microscopic and macroscopic morphologies
used to identify bacteria. Because many orgs can appear very similar,
morphologic characteristics provide a tentative id of the org and are used
to select more discriminating classification methods. Most common
methods consist of measuring presence or absence of specific
biochemical markers (ferment specific carbs, use different compounds as
source of carbon, presence of specific enzymes, biotyping), antigens can
be used in serotyping, antibiogram patterns (analysis of antibiotic
susceptibility) and phage typing.
Analytic classification: used to classify bacteria at the genus, species, or
subspecies level; includes chromatographic pattern of cell wall mycolic
acids, analysis of lipids in the entire cell, analysis of whole cell proteins
and cellular enzymes. Accurate and reproducible, but labor intensive and
instrumentation is expensive; used primarily in reference labs.
Genotypic classification: the most precise method for classifying bacteria
by analyzing their genetic material. Initially ratio of G:C used, now DNA
hybridization, is used for rapid detection and identification, and can
identify organisms without growing them. Nucleic acid sequence
analysis, plasmid analysis, ribotyping, etc are also used, usually to
classify organisms at the subspecies level for epidemiologic investigation,
now simplified to point that clinical labs use them in day-to-day practice.
O. Explain the specific advantages and reasons that characterization of rRNA is
a useful means for determining genetic relatedness of bacteria. (lecture outline)
rRNA is associated with the ribosome, it is critical for protein synthesis, it
binds the Shine-Delgarno sequence/initiation sequence in mRNA, it must
have a secondary structure (base pairs with itself), changes in critical
areas are likely detrimental, and DNA that encodes the rRNA is highly
conserved among bacteria of common ancestry = high sensitivity,
phylogenetic trees are based on rRNA sequences. Gram – are not as
closely related as Gram +, rRNA sequence validates and shows that
mycoplamsa/mycobacteria belong in Gram +.
2. Bacterial Pathogenesis
(Chapters 9, 15, 19; Dr. Briles’ outline)
A. Explain the differences between microbial colonization and infection and give
examples of each process. (p. 83)
Organisms that colonize humans, whether transiently or permanently, do
not interfere with normal body functions. In contrast, disease/infection
occurs when the interaction between microbe and human leads to a
pathogenic process characterized by damage to the human host.
Organisms that colonize humans include normal microbial flora
such as S. aureus, E. coli, C. albicans. Organisms that cause infections
include N.gonorrhoeae, M. tuberculosis.
B. Understand the differences between strict pathogens and opportunistic
pathogens; be able to give specific examples of each and describe host
conditions that are favorable for opportunistic infection. (p.83)
Strict pathogens: are organisms always associated with disease, such as
M. tuberculosis, N. gonorrhoeae.
Opportunistic pathogens: are organisms that are typically members of the
patient’s normal flora that do not produce disease in their normal setting
but establish disease when they are introduced into unprotected sites
(blood, tissues), such as S. aureus, E.coli, C.albicans. If a patient’s
immune system is defective, that patient is more susceptible to disease
caused by opportunistic pathogens.
C. Describe which anatomic locations in the human body contain normal flora
versus those locations which are normally sterile and the major types of bacteria
that comprise the normal flora in each of these sites. (p. 84-86)
Normal flora occurs in the mouth, oroharnx, and nasopharynx
(Peptostreptococcus, Actinomyces), the ear (Staphylcoccus), the eye
(Haemophilus), the esophagus, stomach (H. pylori), small intestine
(anaerobes such as Peptostreptococcus, Porphyromonas), and in very
great numbers in the large intestine (Bifidobacterium, Eubacterium,
Bacterioides,Enterococcus). The anterior urethra (Lactobacillli, streptoand staphylococci) and the vagina (staphylococci, streptococci, and
Enterobacteriaceae) and the skin (Staph, Candida) contain normal flora,
although the skin is a hostile environment that does not support survival of
most organisms.
Normally sterile locations include the lower respiratory tract (larynx,
trachea, bronchioles and lower airways), although transient colonization
may occur, the urinary bladder may also be transiently colonized, the
ureters are generally sterile, and so is the cervix,
D. Describe the beneficial roles of normal flora in the host-microorganism
ecological relationship. (p. 83-87)
The normal commensal population of microbes participates in the
metabolism of food products, provides essential growth factors, protects
against infections with highly virulent microorganisms, and stimulates the
immune response. Some produce vitamins, such as Vitamin K, which
aids in blood clotting.
E. Explain how prolonged hospitalization or antibiotic therapy can affect the
composition of normal flora. (p.83)
The microbial flora in and on the human body is in a continual state of flux,
throughout the life of a human being the microbial population continues to
change. Changes in health can drastically disrupt the delicate balance
that is maintained among the heterogeneous organisms coexisting within
us. Hospitalization can lead to replacement of normally avirulent
organisms in the oropharynx with gram negative rods (Klebsiella,
Pseudomonas) that can invade the lungs and cause pneumonia. The
indigenous bacteria present in the intestines restrict the growth of
Clostridium difficile in the GI tract. In the presence of antibiotics, this
indigenous flora is eliminated, and C.difficile is able to proliferate and
produce diarrheal disease and colitis.
F. Describe the clinical manifestations of endotoxin shock and mechanisms
responsible for these manifestations (p. 197; Figure 19-2)
At low concentrations, endotoxin stimulates the mounting of protective
responses, such as fever, vasodilation, and the activation of immune and
inflammatory responses. However, endotoxin levels in the bloods of
patients with gram negative bacterial sepsis (bacteria in the blood) can be
very high and the response to these acan be overpowering, resulting in
shock and possibly death. High concentrations of endotoxin can also
activate the alternative pathway of complement; promote high fever,
hypotension, and shock, produced by vasodilatation and capillary leakage;
and disseminate intravascular coagulation stemming from activation of
blood coagulation pathways. The high fever, petechiae, and potential
symptoms of shock (from increased vascular permeability) assoc with N.
meningitides can be related to the large amount of endotoxin released
during infection.
Endotoxin-Mediated Toxicity: Fever, leukopenia, followed by leukocytosis,
activation of complement, thrombocytopenia, DIC, decreased peripheral
circulation and perfusion to major organs, shock and death.
G. Describe the similarities and differences between exotoxins and endotoxins,
including structure, mechanism of action, targets, and sources. (p. 196-197)
Exotoxin: proteins that can be produced by gram + or gram – bacteria and
include cytolytic enzymes and receptor-binding proteins that alter a
function or kill the cell. In many cases the toxin gene is encoded by a
plasmid or lysogenic phage. Many are dimeric with A and B subunits.
The B portion binds to a specific cell surface receptor, and the A subunit is
transferred into the interior of the cell where injury is induced. The tissues
targeted are very defined and limited. (Secreted molecules).
Endotoxin: LPS, produced by gram – bacteria, a powerful activator of
acute-phase and inflammatory reactions. The lipid A portion is
responsible for the endotoxin activity, released during infection, binds to
specific receptors on macrophages, B cells and stimulates production and
release of acute-phase cytokines, like IL-1, IL-6, and TNF-α.
H. Describe 3 mechanisms by which exotoxins work and provide examples of
bacterial diseases that are caused by each of them. (p. 198-199)
C. diphtheriae toxin binds to a groth factor receptor precursor, inactivates
elongation factor-2 which prevents protein synthesis by ribosomes,
causing cell death.
V. cholerae toxin binds a ganglioside receptor, activates adenylate cyclase
which increases cAMP levels, causing loss of cell nutrients and secretory
diarrhea.
C. tetani toxin binds a ganglioside receptor on the post-synaptic side of a
nerve/muscle synapse, blocking inhibitory transmitter release, causing
continuous stimulation by excitatory transmitter resulting in spastic
paralysis. C. botulinum binds a ganglioside on the presynaptic side,
blocking release of Ach from vesicles, blocking muscle stimulation
resulting in flaccid paralysis.
I. Explain how bacteria can circumvent destruction by the host immune system in
order to effectively colonize humans and produce disease. (p. 198-201; Box 19-3)
Encapsulation (capsule shields the bacteria from immune and phagocytic
responses, protects from destruction within phagolysosome), antigenic
mimicry, antigenic masking (immunoglobulin G-binding protein, protein A),
antigenic shift (vary structure of surface antigens), production of
antiimmunoglobulin proteases (degrade IgA), destruction of phagocyte,
inhibition of chemotaxis (degrade C5a), phagocytosis (inhibit via capsule
or M protein), phagolysosome fusion (block, prevent release of enzymes),
resistance to lysosomal enzymes (catalase), and intracellular replication
(grow and hide from immune response, disseminate throughout body).
S.aureus esapes host defenses by walling off the site of infection via
production of coagulase, which promotes conversion of fibrinogen to fibrin
to produce a clotlike barrier. M. tuberculosis survives by promoting the
development of a granuloma, within which viable bacteria may reside for
the life of the infected person.
J. Describe 3 mechanisms by which certain bacteria can circumvent phagocytic
killing after ingestion by host phagocytes and provide an example of a bacterial
species that utilizes each mechanism. (p. 200; Table 19-4)
Inhibition of phagolysosome fusion – Legionella, Mycobacteium
tuberculosis, Chlamydia. Prevents contact with its bactericidal contents.
Resistance to lysosomal enzymes – Salmonella typhimurium, coxiella,
Ehrlichia, Mycobacterium leprae, Leishmania. Catalase makes
myeloperoxidase less effective.
Adaptation to cytoplasmic replication – Listeria, Franciscella, Rickettsia.
Escape lysosome and grow in cytoplasm.
K. Explain the differences between active and passive immunization. (p. 159)
Active immunization occurs when an immune response is stimulated
because of challenge with an immunogen, such as exposure to an
infectious agent (natural immunization) or through exposure to microbes
or their antigens in vaccines.
Passive immunization occurs when the injection of purified antibody or
antibody-containing serum provides rapid, temporary protection or
treatment, also newborns receive natural passive immunization from
maternal Ig that crosses the placenta or is present in the mother’s milk.
L. Explain why a polyvalent polysaccharide-conjugate vaccine is used to
immunize infants against invasive pneumococcal disease whereas a polyvalent
vaccine alone is used in adults at risk for invasive pneumococcal disease. (p.
161-162)
Polysaccharides are generally poor immunogens (T-independent
antigens). The immunogenicity of polysaccharides can be enhanced by
chemical linkage to a protein carrier, creating a conjugate vaccine, which
can be administered to infants and children. Polysaccharide vaccines are
less immunogenic and should be administered only to children older than
2 years. (old objectives state that children don’t make Ab to
polysaccharide).
M. Describe the different mechanisms by which host resistance to infection by
extracellular bacteria versus intracellular bacteria occurs. (lecture outline p. 7)
Extracellular bacteria replicate outsie of cells and must avoid being killed
by phagocytes or complement (ex: Staph)
Intracellular bacteria replicate inside cells and must avoid being killed by
phagocytosis and antibacterial properties of lysosomes (ex: TB, typhoid
fever)
3. Bacterial Genetics
(Chapter 5; Dr. Steyn’s outline)
A. Describe differences between the bacterial and human genomes, including
size, composition, arrangement, presence of extrachromosomal elements,
numbers of chromosomes. (p. 35)
The chromosome of a typical bacterium is a single, double-stranded
circular molecule containing approx. 5 million base pairs, an approximate
length of 1.3 mm (~1000x the diameter of the cell). The smallest bacterial
chromosomes (from mycoplasma) are approximately ¼ this size. In
comparison, humans have two copies of 23 chromosomes, which
represent 2.9 x 10^9 base pairs 990mm in length. Eukaryotes usually
have two distinct copies of each chromosome (diploid), bacteria usually
only have one copy (haploid). Because bacteria only have one copy,
alteration/mutation will have a more obvious effect. Structure of the
bacterial chromosome is maintained by polyamines, such as spermine
and spermidine, rather than histones. Bacteria may also contain
extrachromosomal elements, such as plasmids or bacteriophages. These
elements are independent of the bacterial chromosome and in most cases
can be transmitted from one cell to another.
B. Explain three different mechanisms of transfer of genetic information between
bacterial cells: transduction, transformation, and conjugation. (p. 41-44)
Transduction: the transfer of genetic information from one bacterium to
another by bacteriophages, which pick up fragments of DNA and package
them into bacteriophage particles. The DNA is delivered to infected cells
and becomes incorporaed into the bacterial genomes. Can be specialized,
if they transfer particular genes, or generalized if selection of the
sequences is random.
Transformation: the process by which bacteria take up fragments of naked
DNA and incorporate them into their genomes, results in acquisition of
new genetic markers from exogenous or foreign DNA. Both gram + and
gram – can take up and stably maintain exogenous DNA (said to be
competent), competence develops toward the end of logarithmic growth,
some time before a population enters the stationary phase. Most bacteria
do not exhibit a natural ability for DNA uptake, but chemical methods and
electroporation can be used to indroduce DNA.
Conjugation: is the mating or quasisexual exchange of genetic information
from one bacterium (the donor) to another bacterium (the recipient).
Occurs with most, if not all, eubacteria, usually between members of the
same or related species but has been demonstrated between prokaryotes
and cells from plants, animals, and fungi. Results in the one way transfer
of DNA through the sex pilus. Mating type (sex) depends on presence
(male) or absence (female of the F plasmid, which carries all the genes
necessary for it’s own transfer, inducing the ability to make sex pili and
initiate DNA synthesis at the transfer origin of the plasmid. Single
stranded DNA is transferred, recirculizes, and the complementary strand
is synthesized. Integration of the F plasmid into host DNA results in
transfer of part of the plasmid sequence and a portion of the bacterial
chromosome.
**Transposition: Once inside a cell, a transposon, a jumping gene, can
jump between different DNA molecules (plasmid to plasmid or plasmid to
chromosome), or within a single genome. Transposons contain genetic
information necessary for their own transfer, and may contain genes for
resistance against antibiotics. They can insert into and inactivate genes,
sometimes resulting in cell death.
4. Antimicrobial Agents, Chemotherapy and Resistance
(Chapter 20; Dr. Waites’ outline)
A. Describe the differences between antibiotics, antiseptics, and disinfectants.
(lecture outline)
Antibiotic – an agent that can be naturally occurring, partially or
completely synthetic that selectively inhibits the growth of microorganisms
at low concentrations (penicillin)
Antiseptic – an agent used to inhibit or eliminate microbes on the skin or
other living tissue (alcohol, iodine, chlorhexidine)
Disinfectant – an agent used to destroy microbes on inanimate objects
(phenols, formaldehyde, chlorine bleach)
B. Recognize the generic names of all antibiotics and groups discussed in the
lectures and be able to classify them according to mechanism of action. (lecture
outline; Table 20.1),
C. Describe the targets in the bacterial cell where antibiotics act to inhibit growth
and how the various drugs work at each site (e.g., cell wall, cell membrane,
ribosome, DNA replication, etc.) (p. 204)
D. Relate specific antibiotics (or classes of antibiotics) to their major therapeutic
applications and toxicities. (lecture outline)
Beta-lactams: act on cell wall to inhibit growth
Penicillin – binds active site of transpeptidase enzyme (also called
PBPs, penicillin binding proteins) that cross-links peptidoglycan by
joining D-ala and gly; mimics D-alanyl-D-ala that would normally
bind; irreversibly inhibits transpeptidase; broad spectrum, effective
against gram – bacteria.
Cephalosporins – same mechanisms of action as penicillin but
have a wider antibacterial spectrum, are resistant to beta
lactamases and have improved pharmacokinetic properties.
Monobactams – narrow spectrum active only against aerobic,
gram-negative bacteria.
Carbapenems – broad spectrum antibiotics active against virtually
all groups of organisms.
Non-beta lactams acting on cell wall
Cycloserine – inhibits synthesis of D-alanyl-D-ala within cell wall
mucopeptide inhibiting cross linking of peptidoglycan, used to treat
mycobacterial infections.
Glycopeptides (vancomycin) – binds D-ala-D-ala moiety of
precursor subunit blocking transpeptidation (blocks cross linking)
used against growing gram + bacteria.
Bacitracin – complexes with lipid carrier that transports
peptidoglycan precursors from cytoplasm to cell membrane (inhibits
cytoplamic membrane and movement of peptidoglycan precursors),
used for treatment of skin infections caused by gram +, particularly
Staph and group A strep.
Isonazid (INH) – inhibits fatty acid and lipid components of mycolic
acid synthesis in mycobacteria, bactericidal against actively
replicating mycobacteria.
Agents acting on bacterial ribosome
Streptogramins – bind 50s, prevent peptide elongation and
premature release from ribosome, effective against staphylococci,
streptococci, and E. faecium.
Oxazolidinones – bind 50s and prevent formation of initiation
complex, active against all staphylococci, streptococci and
enterococci.
Aminoglycosides – bind 30s, inactivate initiation complex, misread
mRNA genetic code and prematurely release peptide, used to treat
serious infections caused by many gram – rods and some gram +
orgs, anaerobes are resistant.
Chloramphenicol - bind 50s, prevent peptide bond formation, broad
spectrum not commonly used in US because it disrupts protein
synthesis in human bone marrow cells and can cause blood
dyscrasias.
Clindamycin – bind 50s, prevent peptide bond formation, active
against staphylococci and anaerobic gram – rods, generally
inactive against aerobic gram -.
Macrolides – bind 50s, prevent release of deacylated tRNA
preventing peptide elongation, bacteriostatic with a broad spectrum
of activity, most gram – are resistant.
Tetracyclines – prevent attachment of tRNA-AA to 30s, broad
spectrum, effective against Chlamydia, mycoplasma, rickettsia and
other selected gram + and gram -.
Agents interfering with Cell Membranes
Polymyxins – cyclic polypeptides derived from B acillus polymyxa,
insert into bacterial membranes like detergents, increasing cell
permeability and eventual cell death. Used for localized infections,
against gram – rods.
Daptomycin – disrupts cell membrane function, binds the
membrane and causes rapid depolarization resulting in a loss of
membrane potential leading to inhibition of DNA, RNA, and protein
synthesis. Active against gram + only.
Agents interfering with DNA Replication
Rifampin – binds DNA-dependent RNA pol, prevents mRNA
transcription, bactericidal for Mycobacterium tuberculosis and
active against aerobic gram + cocci, including staph and strep.
Metronidazole – intermediate metabolites damage DNA in
anaerobes, effective in treatment of amebiasis, giardiasis and
serious anaerobic infections.
Fluoroquinolones – bind to DNA gyrase and Topoisomerase IV,
inhibiting DNA rep, excellent activity against gram + and gram –
bacteria.
Antimetabolites
Sulfonamide – inhibits dihydropteroate synthase, disrupts folilc acid
synthesis, active against broad range of gram + and gram – such
as Nocardia, Chlamydia, and some protozoa.
Trimethoprim – inhibits dihydrofolate reductase, synergy with
sulfonamide (used together).
E. Be able to list and describe desirable properties and requirements of
antibiotics useful in treating microbial infections in the human host. (lecture
outline)
Selective toxicity, water soluble, bactericidal, high serum levels achieved
for several hours, broad spectrum, minimal effect on normal flora, low
potential for inducing resistance, minimal side effects/toxicity.
F. Be able to list and describe 5 mechanisms of antimicrobial drug resistance and
give specific examples of each. (lecture outline)
Decreased permeability – Aminoglycosides, resistance caused by
inhibited transport of the antibiotic into the bacterial cell.
Active Efflux – Erythromycin, actively exporting the antibiotic out of the
cell.
Altered Target – Fluoroquinolones, mutation of genes for binding sites
(DNA gyrase and topoisomerase)
Metabolic Bypass – Trimeth/sulfa, bacterial strains develop alternative
enzyme systems to synthesize folic acid
Enzyme inactivation – Penicillin, bacteria produce β-lactamases that
inactivate the beta-lactam antibiotics.
G. Understand the difference between innate and acquired antibiotic resistance
and give examples of each. (lecture outline)
Innate – Primary resistance, the natural resistance bacteria possess to
some antimicrobials. For example, organisms may be naturally
impermeable to some antibiotics due to their cell structure. Organisms
with innate resistance are often of low virulence, but, because they are
resistant to many agents, they persist in the environment.
Acquired – An organism can acquire resistance to an antimicrobial to
which it was previously sensitive. This can be due to chance mutation in
the genetic material of the cell, or the acquisition of resistance genes from
other drug resistant cells.
H. Understand the concept of clonal spread as it relates to transmission of
antimicrobial resistant bacteria. (lecture outline)
Old outline: Clonal spread refers to the fact that bacteria can mutate and
become resistant to certain drugs, and a person with a drug-resistant
strain of bacteria can spread it to others.
I. Understand differences between bactericidal and bacteriostatic drugs and how
this relates to drug choice in specific clinical settings. (lecture outline)
Bactericidal – level of antimicrobial activity that kills the organism.
Bacteriostatic – level of antimicrobial activity that inhibits growth of an
organism.
Old Objectives: In most infections, bacteriostatic drugs are used because
preventing the bacteria from dividing is generally enough to stop the
infection. Caution must be taken when prescribing combination therapy
because a drug such as penicillin, which can act only when the bacteria is
dividing, used in combination with tetracycline, a bacteriostatic drug which
stops bacteria from dividing, would be antagonistic.
J. Explain the rationale for antibiotic prophylaxis and combination therapy.
(lecture outline)
Antimicrobial prophylaxis can prevent endocarditis following dental work,
provide protection for contacts of meningococcal meningitis, prevent
opportunistic infections in AIDS, recurrent UTIs and post-surgical
infections.
Combination therapy (old outline) provides a broader spectrum for
infection of unclear etiology, polymicrobial infections, prevents emergence
of resistance (mycobacterium), infections difficult to eradicate
(immunosuppressed host), and synergy (drugs enhance effects of other
drugs).
K. Know major characteristics of bacteria that favor development of drug
resistance. (lecture outline)
- Intrinsic resistance to some drugs
- Ability to exchange genetic information
- Ability to survive adverse environmental conditions
- Easily colonize, infect, and transmit
- Reservoirs in body
L. Explain the reasons why drug resistance in bacteria is increasing in the
hospital and community and its consequences to the health care system. (lecture
outline)
Resistance increases in hospitals due to greater severity of illness,
immunocompromised patients, new devices and procedures, ineffective
infection and control practices, increased use of antimicrobial prophylaxis,
and empiric polymicrobial antimicrobial therapy.
Its consequences are prolonged illness/hospitalization, increased mortality,
inappropriate therapy, more expensive/toxic therapy, more lab tests, and
the spread of infectious organisms that may have no effective treatment
and that may be impossible to eradicate from the hospital.
M. Discuss significance of emerging drug-resistant bacteria in the hospital and
community including: S. aureus, E. faecium, S. pneumoniae, ESBL-producing E.
coli and Klebsiella spp., and P. aeruginosa. (lecture outline)
5. Anaerobic Bacteria
(Chapters 40, 41, 42; Dr. Moser’s outline)
A. Describe 2 enzyme systems that are lacking in strict anaerobes and why the
lack of these enzymes renders oxygen toxic to them (lecture outline)
Superoxide dismutase (SOD) and catalase, detoxify high energy radicals
such as hydrogen peroxide produced from oxygen metabolism that
otherwise kill the cell. Cytochrome systems normally turn radicals into
water and atmospheric oxygen via these enzymes.
B. Describe the anatomic sites where anaerobes are normal flora. (p. 83-87)
Colon (over 90% are anaerobes), mouth, vagina, skin.
C. Learn clinical characteristics, responsible organism(s), and mechanisms of
disease for these conditions caused as described in the lecture and assigned
reading:
Periodontitis – chronic, progressive receding of the gums due to the toxins
being produced by the bacteria that are hiding in crypts. No matter how
good the teeth are, eventually the gums are gone and they can’t hold their
roots into the bone. Caused by Acinetobacter spp.
Brain and lung abscess - if you have poor dentition and your teeth are
loose or you get your teeth cleaned, activity can cause a showering of oral
bacteria. That puts you at risk if, for example, you have a defective heart
valve, you could get endocarditis. If it’s chronic, it may get to the brain
and cause an abscess. Brain abscesses usually due to gram + rods, cocci,
and a few gram -: Bacteriodes, Prevotella, and Porphyromona. Aspiration
pneumonia, the classic example is an alcoholic who passes out and they
regurgitate stomach acid and contents and they aspirate. They get oral
flora and foreign body material from the stomach and acid. All of that
destroys tissue and once you get destroyed tissue, anaerobes are happy
because they have a place to hide from oxygen. They will cause
abscesses and bacteremias as well. Often due to Actinomyces.
Vincent’s Angina – acute dental infection, all gram negative. Treponema
are very thin and corkscrew-like. Fusobacterium are long and fusiform.
The short fat rods are probably Prevotella/Bacteroides. There is
overgrowth of these organisms that are normally there, but because of
poor oral hygiene have multiplied and cause damage.
Gas gangrene - a very active infection. In the Civil War, people got
wounded in the trenches and they lost their arms or legs due to this
infection. There are a number of toxins, but the most important one in gas
gangrene is Phospholipase C, also called alpha-toxin or lethal toxin. It
takes your tissue and makes hydrogen gas and CO2 out of it. That’s why
it has gas in the tissue. Gangrene means dead tissue and gas is in the
dead tissue, so you can poke it and it feels like packing material. It has
about 12 possible toxins that do lots of things. Basically, it chews up your
tissue. Often caused by C. perfringens.
Lumpy Jaw - Actinomycosis. The face becomes asymmetric; normal face
on one side and greatly swollen on the left side. Looking down at the root
of the crown and looking at the x-ray, you see the roots and the bone are
being eaten away. An abscess forms and is quite painful. People will
come in to have it looked at and if you leave it alone they make these
draining sinuses. This will come out the side of the jaw. If it’s opened up
and put some gauze on it, the gauze soaks up the fluid and you can
capture the sulphur granules and diagnose without having to go into the
abscess inside, but not everyone waits this long. This is the classic
description of Actinomyces israelli infection.
Tetanus - step on a nail, get a splinter, some kind of gross contamination
of a wound and the organisms spores in the environment are now in your
tissue and they grow and produce this toxin called tetanospasm.
Tetanospasm blocks the inhibitory neurotransmitters, the gammaaminobutyric acid and glycine. That causes the inability to relax the
muscle, so you get constant firing of muscles. This is lockjaw. It’s called
“sardonic smile,” because the muscles are clamped and you can’t undo
them. Caused by Clostridia, gram + spores.
Botulism - aka food poisoning. It’s mostly pre-formed toxin that we
ingest. This organism lives in the soil and it can come from poor handling
of foods, improper canning. Bacterial spores are harder to kill than cells,
so there has to be higher temperature and pressure and it takes a period
of time to kill them all off. If canning isn’t done properly and all the spores
aren’t killed then the organism grows in the anaerobic environment. This
toxin is extremely toxic; it does not take much of it. This toxin blocks Ach
and you don’t get firing of the muscles and you get flaccid paralysis. It’s
the opposite of tetanus. This is a problem as it progresses because the
diaphragm is a muscle and it quits firing. That’s why most of the treatment
is support and can include ventilators to maintain the patient until they
recover.
An exception to it being pre-formed is infant botulism. Infants don’t have a
GI flora established yet, they’re not born with one, and so over time they
pick up bacteria that colonize the GI tract and that protects against
introduction of different organisms. If during that period of time, they’re
exposed to Clostridium botulinum and the classic way this happens is by
giving them honey. Honey is environmental and it can have spores from
the organism and you get production in the GI tract. This still occurs
occasionally and it’s the opposite of the usual ingestion of pre-formed
toxin from food. Caused by Clostridium botulinum.
Pseudomembranous colitis - C. difficile colitis, antibiotic associated.
Patients present with diarrhea, fever, and abdominal pain.
D. Understand how laboratory diagnosis of the above anaerobic infections is
achieved.
Gram stain: may be helpful in establishment of a mixed infection or the
presence of clostridia in wounds
Culture: sample collection and transport are critical, require complex
medium supplemented with hemin, vitamin K and/or blood, should include
media containing antibiotics (aminoglycoside) to suppress facultative
anaerobes, incubation and work up perfomed in CO in nitrogen/hydrogen
mix.
Anaerobic infections generally have a foul smelling discharge, are located
close to a mucosal surface, cause gas in tissue, have abscess formation.
E. Explain differences between gaseous requirements for bacterial growth,
including microaerophiles, capnophiles, obligate anaerobes, obligate aerobes,
facultative anaerobes, aerotolerant anaerobe. (p. 25; lecture outline)
Aerobic: require oxygen as electron acceptor (respires)
Microaerophilic: require oxygen in reduced quantity, can grow without
Capnophilic: require carbon dioxide
Obligate anaerobes: cannot survive in presence of oxygen, always
ferments
Obligate aerobes: cannot survive without oxygen, cannot ferment
Facultative anaerobes: can grow with or without oxygen, can respire or
ferment
Aerotolerant anaerobe: grows with or without oxygen, always ferments
Important concepts related to specific groups of bacteria
Chapters: 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 43,
44, 45,
46, 47; Lecture outlines from Drs. Benjamin and Waites)
Listed below are specific examples of important concepts related to major
bacterial
groups and species and their diseases that should be learned in addition to the
characteristics of individual bacteria.
A. Gram-positive cocci and bacilli
1. How do Protein A and the P-V leucocidin aid Staphyloccoccus aureus in
causing disease? (lecture outline)
Protein A coats the surface of most S. aureus and inhibits antibodymediated clearance by binding IgG (1,2,4) Fc receptors. Binding the Fc
region of IgG inhibits the Fab region from binding and opsonizing the
bacteria. It can also bind antibodies and form immune complexes with the
subsequent consumption of complement.
P-V leukocidin toxin lyses white blood cells. Cell lysis by these toxins is
mediated by pore formation with subsequent increased permeability to
cations and osmotic instability.
2. What advantage does the presence of coagulase confer on Staphylococcus
aureus?(lecture outline)
S. aureus has two forms of coagulase: bound and free. Coagulase bound
to the cell wall can directly convert fibrinogen to insoluble fibrin and cause
the staph to clump. Cell-free coagulase does the same thing by reacting
with globulin plasma factor (coagulase reacting factor) to form
staphylothorombin (thrombin-like). This factor catalyzes the conversion of
fibrinogen to insoluble fibrin. Coagulase may cause the formation of a
fibrin layer around a staph abscess, localizing the infection and protecting
it from phagocytosis.
3. Explain the concept of a “superantigen” and how the staphylococcal toxic
shock toxin initiates tissue damage in the Toxic Shock Syndrome. (p. 224)
Superantigens belong to a class of polypeptides that bind MHC II on
macrophages, which interact with T-cell receptors, leading to non-specific
proliferation of T-cells and release of cytokines with subsequent tissue
damage. Examples: exfoliative toxin A, enterotoxins, TSST-1. In TSS,
Toxic shock syndrome toxin-1 stimulates the T-cells (as above) and
causes leakage or cellular destruction of endothelial cells.
4. How does catalase assist organisms such as staphylococci resist destruction
by the host immune response? (lecture outline)
Hydrogen peroxide can accumulate during bacterial metabolism or after
phagocytosis. All staph produce catalase, which catalyzes the conversion
of hydrogen peroxide to water and oxygen.
5. Compare and contrast the virulence factors and diseases caused by
Staphylococcus aureus versus the coagulase-negative staphylococci. (p. 228233)
S. aureus:
Virulence factors:
Structural components - capsule, peptidoglycan, teichoic acid,
Protein A, cytoplasmic membrane
Toxins – Cytotoxins, exfoliative toxins, enterotoxins, TSST-1
Enzymes – coagulase, catalase, hyaluronidase, fibrinolysin, lipases,
nucleases, penicillinase
Diseases:
Toxin-mediated: food poisoning, TSS, scalded skin syndrome
Pyogenic: impetigo, folliculitis, furuncles, carbuncles, wound
infections
Other systemic disease (associated with bacteremia): pneumonia,
empyema, septic arthritis, osteomyelitis, acute endocarditis,
catheter-related bacteremia
Coagulase-negative staph:
Virulence factors:
Everything except coagulase?
Diseases:
Endocarditis, Wound infections, UTI, catheter and shunt infections,
prosthetic device infections
6. Acute glomerulonephritis and rheumatic heart disease are both autoimmune
sequelae of Group A streptococcal infections. Explain their similarities and
differences with respect to immune mechanisms involved and clinical
manifestations. (p. 244-245)
These are both nonsuppurative (non-pus forming) streptococcal diseases.
Rheumatic fever is a complication of S. pyogenes disease, characterized
by inflammatory changes of the heart, joints, blood vessesl and
subcutaneous tissue. Rheumatic fever is associated with strep pharyngitis
and not cutaneous strep infections. It is most common in young children.
There is no specific diagnostic test and diagnosis is made based on
evidence of a recent S. pyogenes infection.
Acute glomerulonephritis is characterized by inflammation of the glomeruli
with edema, hypertension, hematuria and proteinuria. Specific
nephritogenic strains of Group A streptococci are associated with the
disease and there are both pyodermal and a pharyngitis associated
strains. Diagnosis is made based on evidence of a recent S. pyogenes
infection. Children usually recover uneventfully, but loss of renal function
has occurred in adults.
7. How can a recent Group A streptococcal infection be diagnosed in someone
who has already taken antibiotics? (p. 242)
S. pyogenes release the virulence factors streptolysin O and streptolysin S.
Streptolysin S is non-immunogenci whereas antibodies against
streptolysin O are readily formed in infected people. The anti-ASO test is
useful for documenting recent Group A infections. Antibodies against
streptokinase can be used as a marker for infection. Antibodies against
DNase B are a marker for cutaneous S. pyogenes infection because these
infections do not cause formation of antibodies against streptolysin O
because strep O is inhibited by cholesterol in skin lipid.
8. Explain the role of bacteriophage lysogeny in pathogenesis of some
streptococcal infections. (p. 243)
Scarlet fever is a complication of streptococcal pharyngitis that occurs
when the infecting strain is lysogenized by a temperate bacteriophage
(does not cause immediate lysis) that stimulates the production of
pyrogenic exotoxin.
9. Describe the pathogenesis of streptococcal necrotizing fasciitis. (p. 244)
Lay term: “flesh-eating bacteria” Occurs deep in the subcutaneous tissue
and spreads along the fascia. Characterized by destruction of fat and
muscle. The organism is introduced through a break in the skin. Initially,
there is cellulitis, after which bullae form and gangrene and systemic
symptoms develop. Systemic toxicity, multiorgan failure and death are
hallmarks. Unlike cellulitis, which can be treated with antibiotics, fascitis
requires surgical removal of the infected tissue. subcutaneous air is
classically described in necrotizing fasciitis
10. Explain the basis for the Lancefield groups and how they are used to classify
the streptococci? (lecture outline)
Lancefield groups differentiate beta-hemolytic organisms based on groupspecific antigens that are typically cell wall carbohydrates. These antigens
can be readily detected with immunologic assays and are used to identify
strep pathogens. For example, S. pyogenes is group A. Most, but not all,
alpha-hemolytic and nonhemolytic strep do not possess the group-specific
antigens. The scheme is used to identify a few species of strep: A, B, C, F,
G.
11. Explain why the Enterococcus is especially well-suited to be a nosocomial
pathogen. (p. 260-262)
Enterococcus is part of the normal flora of the GI tract and is Inherently
resistant to common antibiotics (cephalosporin) or have acquired
resistance genes (vancomycin). Thus patients being treated with broadspectrum antibiotics (and are typically already ill) are highly susceptible to
infection. Cell wall structure typical of gram-+ bacteria allows them to
survive on environmental surfaces for prolonged periods.
12. What unique features of Bacillus anthracis help to differentiate from other
Bacillus species in the clinical laboratory? (p. 267)
Identification is based on microscopic (gram -, nonmotile rods) and
colonial morphology (non-hemolytic, adhering). Confirmed by
demonstrating capsule and either lysis with gamma phage or positive DFA
test for specific capsular polysaccharide.
13. Discuss the features of Bacillus anthracis that make it such a logical
organism for bioterrorism attacks. (p. 265-269)
Spores can be grown in culture with low CO2 and are long-lived outside a
host. Low infectious dose. Spores can be treated to minimize clumping
so they reach the lower airway. Inhalation anthrax is usually fatal.
14. Describe the epidemiology and pathogenesis of meningitis due to Listeria
monocytogenes, Escherichia coli, Streptococcus agalactiae, Neisseria
meningitidis, and Haemophilus influenzae and emphasize the differences and
similarities among them.
Listeria monocytogenes:
- facultative, intracellular pathogen that grows in macrophages, epithelial
cells and fibroblasts and can avoid antibody-mediated clearance
- causes meningitis in neonates, elderly, pregnant women, and patients
with defects in cellular, but not in humoral immunity
- acquired by ingestion of contaminated food, it may be asymptomatic in
healthy adults
the organism can cross the placenta and cause spontaneous abortion
and stillbirth
E. coli:
- normal flora of GI
- neonatal meninigitis, not caused by endogenous bacteria
- approximately 75% of E. coli strains possess the K1 capsular antigen
- this serogroup is also commonly present in the GI tracts of pregnant
womand newborn infants
-
Neisseria meningitidis:
- purulent inflammation of meninges associated with headache,
meningeal signs, and fever
- high mortality rate unless promptly treated with effective antibiotics
- approx. 0.6 cases per 100,000 population reported in 2004
- very young children may have only nonspecific signs such as fever or
vomiting
- incidence of neurologic sequelae is low, with hearing deficits and
arthritis most commonly reported
Haemophilus influenzae:
- used to be a common cause of pediatric meningitis, but not anymore
due to wide use of conjugated vaccines
- dz in non-immunized patients results from bacteremic spread of the
organisms from the nasopharynx and cannot be differentiated clinically
from other causes of bacterial meningitis
- initial presentation is 1-to-3 day history of mild upper respiratory dz
after which the typical signs of meningitis appear
Streptococcus agalactiae:
- carried in GI tract of pregnant women as normal flora
- if acquired by baby at delivery, can cause severe pheumonia and
severe meningitis
- most common cause of septicemia and meningitis in newborns
- approximately 60% of infants born to colonized mothers become
colonized with their mother’s organisms
- risk factors for neonatal colonization—premature delivery, prolonged
membrane rupture, intrapartum fever
- serotypes most commonly assoc. with neonatal dz are Ia, III, and V.
- serotypes Ia and V are the most common in adult dz
- colonization of neonate can occur in utero, at birth, or during the first
few months of life
- risk of adult dz greater in pregnant women than in men and
non-pregnant women
B. Gram-negative bacilli
1. Compare and contrast diarrheal diseases caused by Salmonella, Shigella,
Campylobacter, Staphylococcus aureus, Bacillus cereus, Escherichia coli,
Yersinia,and Vibrio species with respect to epidemiology, modes of transmission,
mechanism (infection vs. intoxication), and invasiveness.
Epidemiology
Transmission Mechanism Invasiveness Disease
Salmonella
S. typhi and S. Contaminated Low
Limited to
Gastroenteritis,
paratyphi only food; fecalinfectious
GI tract
septicemia,
infect humans
oral spread in dose for S.
enteric fever,
children
typhi
asymptomatic
Shigella
Humans are the Fecal-oral
Highly
Limited to
Bacterial
only host
infectious, colon
dysentery,
S.
epithelium
Gastroenteritis
dysentery
(shigellosis)
produces
Shiga toxin
Campylobact Zoonotic
Contaminated Infection;
C. jejuni
Acute enteritis
er
infection
food and
usually
damages lg. with diarrhea
water
self-limited intestine
mucosa
S. Aureus
Protein food
Preformed Infection is
Watery
enterotoxin short-lived
diarrhea
~24 hrs
B. cereus
Starchy food, Preformed
Watery
spores
enterotoxin
diarrhea
E. coli
Traveler’s
diarrhea
Yersinia
Zoonotic
Flea bite or
Infection
Resists
Bubonic
infection
direct contact
phagocytosis plague (Y.
with infected
and spreads pestis);
tissue
gastroenteritis
Vibrio
Serotype O1
Contaminated Cholera
Limited to
Cholera starts
causes
water; High
toxin,
GI
with watery
pandemics
infectious
causes
epithelium
diarrhea, can
dose, killed
secretion
progress to
by stomach
of
hypovolemic
acid
electrolytes
shock;
and water
gastroenteritis
Salmonella- most infections from contaminated food, direct fecal-oral
spread in children(grows black on XLD agar- shows H2S). Salmonella
really invades our cells. It causes a profuse diarrhea. Salmonella causes
a few million cases of food borne illness each year in the US. Most of it is
not so severe that it is identified. There are 2400 serotypes, but there are
only 2 of those that cause 40-50% of all salmonella outbreaks- enterica
Typhimurium, and enterica enteritidis are the most common. You have
vomiting and perfuse diarrhea for 8-48 hours after you start developing
symptoms and this then resolves in 7-10 days. The source of salmonella
is usually our meat animals or people. The way to prevent this organism
is to cook it. (Don’t cut chicken and salad on the same cutting board or
use the same knife!)
Shigella- causes bacillary dysentery, a high volume, watery diarrhea. It
invades the colon epithelium and can be treated with Ampicillin or Bactrim.
Humans are the only normal host. 200 organisms is an infectious dose,
which is a very low amount in comparison to most bacterial infections. It
can be transmitted by the 4Fs: feces, fingers, food, flies, and water. It can
be controlled by washing your hands and other sanitary measures in
society. Common sites of this disease are nursing homes, day cares,
wars, and cruise ships. It causes 15% of the pediatric diarrhea in the US.
Campylobacter- It causes a bloody diarrhea. It is more common and less
severe than Salmonella. It is carried by food animals and pets. Most
human infections are from contaminated food and water sources.
Treatment consists of rehydration. You can prevent this organism through
cleanliness and cooking your food.
Staph aureus- causes watery diarrhea. It is a preformed enterotoxin that
is heat stable. It is in foods such as ham, cream-filled cakes, and potato
salad. It’s toxins infect kittens and non-human primates. The effects of
this organism usually last less than 24 hours.
Bacillus cereus- is a preformed enterotoxin that is heat stable. The
diarrhea produced is profuse and watery. Several of the symptoms are
much like staph. The difference is that the foods are typically a starchy
food instead of a protein rich food. Those spores will germinate after it is
cooked, grow in the rice, and then refry the rice and kill the organisms
again, but the toxin will stay around and cause disease. A large number
of spores germinate in vivo.
E. coli- causes secretory diarrhea or watery diarrhea. Features of this
diarrhea include stimulation of net intestinal secretion, no morphological
damage, and no impairment of Na- dependent solute absorption. Species
of E.coli are responsible for traveler’s diarrhea and infantile diarrhea.
Eneterovasive E. coli (EIEC) causes bacillary disentry. The most common
outbreak strain in food borne illness is EHEC, or Enterohemorrhagic E.
coli. The diarrhea present is usually mild.
Yersinia- is an enterobacteriaceae but it is not food borne. It causes a
systemic disease much like salmonella typhi. It causes the bubonic and
pneumonic plague and is contracted by flea infected bites. It causes
septicemia and often death. Pneumonic plague is passed from person to
person coughing up the organisms. The plague in 14th century Europe
killed 25 million people and was often of the pneumonic type. Bubonic
plague can result in 75% mortality with a few days; the pneumonic form
can result in greater than 90% mortality within 24 hours. Control of rat
populations concurrent with elimination of their fleas prevents spread of
the plague to humans. Decontamination of water and milk prevents
gastroenteritis. Treatment of the plague must be rapid and aggressive. Y.
pestis is generally susceptible to streptomycin and chloramphenicol but
concomitant therapy is sometimes recommended. Treatment of Y.
enterocolitica infections usually involves the use of ampicillin or
tetracycline.
Vibrio- Toxins produced in vivo. It produces a profuse watery diarrhea. It
is spread by contaminated water. Stomach acid offers protection. An
infectious dose is 107 CFU. It has a 1-5 day incubation period.
Rehydration by fluids is sufficient treatment.
2. Describe 4 characteristics that can be used to define the family
Enterobacteriaceae (p. 323)
gram -, facultative anaerobe, oxidase negative, ferment lactose,
resistance to bile salts, all have enterobacterial common antigen, nonspore forming, reduce nitrate, catalase positive, either nonmotile or motile
with peritrichous flagella, some have capsule
3. Which property of Helicobacter pylori enables it to reside in the stomach at pH
of 2 and how does this relate to the ability of the organism induce an
inflammatory reaction? (p. 352)
Produces urease, which neutralizes gastric acid with ammonia. Heat
shock protein enhances the expression of urease. Acid-inhibitory protein
induces hypochlorhydria by blocking acid secretion from parietal cells.
4. Which virulence factor of Pseudomonas aeruginosa contributes to its
pathogenesis in burn patients? (p. 359)
The capsule anchors cells to epithelia, protects the organism from
phagocytosis and antibiotic activity and suppresses neutrophil activity.
Moist surface of the burn and the lack of a neutrophilic response to tissue
invasion predispose patients to infection. Topical antibiotics are
ineffective.
Other outline: Exotoxin A: disrupts protein synthesis by blocking peptide
chain elongation in eukaryotes. Contributes to dermatonecrosis in burn
wounds and is immunosuppressive.
5. Discuss the relative organism load needed to cause diarrheal disease due to
Escherichia coli, Shilgella spp., Salmonella spp. and Vibrio cholera. (lecture
outline)
E. coli: not listed in the hand out. But, from lab and other sources, the
number has to be relatively high since it is part of our normal flora. I think
the number is somewhere around 10^6. Also could be opportunistic.
Shigella spp.: 200 organisms. However, there are approximately 10^8
colony forming units/gram (CFU/g) in infected stool samples.
Salmonella spp.: Low dose needed for S. typhi
Vibrio cholerae: 10^7 CFU. Stomach acid will kill most of it.
6. Explain the difference between osmotic and secretory diarrhea. (lecture outline)
Osmotic diarrhea occurs when too much water is drawn into the bowels.
Occurs with maldigestion, lactose intolerance and laxatives.
Secretory diarrhea occurs when there is an increase in the active
secretion or an inhibition of absorption. There is little to no structural
damage. Fasting will not control diarrhea. E.g. cholera.
7. What is the hemolytic-Uremic Syndrome and how is it related to bacterial
infection?(lecture outline)
Hemolytic-uremic syndrome is characterized by microangiopathic
hemolytic anemia, acute renal failure and thrombocytopenia. It is one of
the most common causes of sudden, short-term kidney failure in children.
Most cases of HUS occur after an infection of the digestive system by E.
coli. Some people have contracted HUS after swimming in pools or lakes
contaminated with feces.
C. Fastidious bacteria
1. Describe the process by which Mycoplasma pneumoniae attaches to the
respiratory epithelium and produces pneumonia. (lecture outline)
P1 is an adhesion protein that ineracts specifically with sialated
glycoprotein receptors at the base of cilia on the epithelial cell surface.
Ciliostasis occurs, and then the cilia and the epithelial cells are destroyed.
This interferes with the clearance of the airways and permits the lower
airway to be contaminated with microbes. This leads to a persistent
cough.
2. Explain the differences in clinical manifestations, epidemiology, natural history,
and pathogenesis of pneumonia caused by Streptococcus pneumoniae,
Staphylococcus aureus, Klebsiella pneumoniae, Mycoplasma pneumoniae,
Chlamydophila pneumoniae,Haemophilus influenzae, and Legionella
pneumophila.
(C2page9)
BUG
Streptococcus
pneumonia
Clinical Manifestations
-onset abrupt
-severe shaking chill and
sustained high fever
-often preceeded by
symptoms of viral resp. tract
infection 1 to 3 days before
onset
-chest pain, blood-tinged
sputum
-often lobar pheumonia,
associated with aspiration
Epidemiology
-common inhabitant of throat and
nasopharynx in healthy people
-common cause of bacterial
pneumonia
-500,000 cases in US annually
Natural History
Pathogenesis
-endogenous oral organisms
are aspirated into the lower
airways
Staphylococcus
aureus
-radiograph reveals patchy
infiltrates with abscesses
Clinical presentation NOT
unique
-seen in very young and elderly and
patients with underlying or recent
pulmonary disease
-severe form of necrotizing
pneumonia with septic shock and
high mortality
Klebsiella
pheumoniae
-thick non-purulent blood
sputum
-25-50% mortality
-community-acquired primary
lobar pneumonia
Mycoplasma
pheumonia
-atypical interstitial “walking”
pheumonia
-clinically similar to the other
pheumonias
-all ages affected, but more
common in younger persons
-reinfection common—no
protective immunity
Chlamydophila
pheumoniae
-frequently asymptomatic
-acute lower respiratory
illness, pharyngitis, sinusitis
-persistent cough and malaise,
but normally does NOT
require hospitalization
-similar to mycoplasma
Most infectious occur in adults
Diagnosis difficult
Infections transmitted person-toperson by respiratory secretions
-NO animal reservoir identified
-inflammation and
consolidation of the lungs
observed primarily in the
elderly with underlying
chronic pulmonary dz
-commonly colonize pts. Who have
chronic pulmonary dz
-frequently assoc. with
exacerbation of bronchitis and
frank pneumonia
-respiratory aerosol dissemination
-2-10 day incubation period
-requires antibiotic therapy
-15-20% mortality rate;
higher if diagnosis delayed
-multilobar
-Legionnaire’s Dz
-severe pneumonia
-epidemic, sporacid
-no person-to-person spread
-epidemic dz in late summer and
autumn
-there is normally an underlying
pulmonary dz
Haemophilus
influenzae
Haemophilus
influenzae
(cont’d)
Legionella
pheumophila
-consolidation and abscess
formation in lungs
-can occur by aspiration or
from the hematogenous spre
of the organism from distan
sites
Predisposing factors:
-hospitalization
-respirator
-increased age
-alcoholism
-Diabetes Mellitus
1980s labs testing
antibody on people
with respiratory
infection were getting
lots of positive tests
for Chlamydia psittaci,
but they hadn’t been
around birds, so this is
when they realized it
was another type of
Chlamydia (now
called Chlamydophila
pheumoniae)
American Legion
Conference, disease
spread through AC
ducts and water supply
(possibly) and infected
many Legionnaires,
hence the name.
-necrosis and abscess
formation
-cytadherence: P1 and other
proteins
-altered macromolecular
synthesis
-induction of inflammation
-human pathogen
???
-typically caused by
nontypeable strains
-endogenous infection by
normal flora
-antiphagocytic capsule
-endotoxin damages resp.
epithelium leading to bacter
spread
-IgA protease
-organism can survive in
moist environments for a lo
time, at high temps. And in
presence of disefectant like
chlorine
-organism proliferates in
water reservoirs during war
months
3. Discuss the impact of the Hib vaccine on epidemiology and spectrum of
disease caused by Haemophilus influenzae in adults and children. (lecture
outline)
H. influenza type b (Hib) was a leading cause of meningitis and
pneumonia in children under five years old, causing an estimated 20,000
cases a year in the early 1980s. Since routine vaccination, the incidence
of Hib disease has declined by greater than 99%. Infections in adults
have also decreased (herd immunity) because prior to vaccination some
children carried Hib in their nasal passages for extended times before they
cleared the infection.
4. Explain why Haemophilus influenzae must be supplied with X and V factors in
order to grow on trypticase soy agar. (lecture outline; p. 372)
H. influenzae require specific growth factors that are released from lysed
blood cells: Intracellular heme (X factor) and NAD (V factor). These
factors are not generally present in standard growth media. They will
grow on chocolate agar unless it has been overheated, destroying V factor.
5. Explain why Bordetella pertussis infections have increased in adolescents and
adults in the United States over recent years. (lecture outline)
B. pertussis is a human disease. Once considered a pediatric disease,
there has been an increase in older children and adults, due to waning
immunity and the selection of strains that are not recognized by the
current vaccines.
6. Compare and contrast the diseases of diphtheria and pertussis, including their
epidemiology, pathogenesis, and prevention. (lecture outline)
Pertussis: aka. whooping cough
Epidemiology: human is the only host; children less than one year
old are at greatest risk, but increasing in adults; spread by person
to person contact
Pathogenesis: Bacteria attach to ciliated epithelial cells, proliferate
and produce localized tissue damage and systemic toxicity.
Produce pertussis toxin that leads to increased cAMP levels and
subsequent increased respiratory secretions and mucus.
Prevention: vaccination of inactivated pertussis toxin and a
bacterial component; given over a number of years up to age 7
Diptheria:
Epidemiology: asymptomatic carriers and unvaccinated hosts;
humans only host, carried in nasopharynx and on skin; spread
person to person by droplets and skin contact; highest risk are
children and immunosuppressed
Pathogenesis: exotoxin (classic A-B exotoxin) secreted at the site
of infection stops host cell protein synthesis. Organism does not
need to enter bloodstream to cause systemic symptoms.
Prevention: immunize with diphtheria toxoid. Given to all children,
booster every 10 years.
7. Explain why the initial outbreak of legionellosis in 1976 was so difficult to
characterize initially. (lecture outline)
The Legionella bacterium was first identified in the summer of 1976 during
the 58th annual convention of the American Legion, which was held at the
Bellevue-Stratford Hotel in Philadelphia. The presentation of affected
persons ranged from mild flulike symptoms to multisystem organ failure.
Of the 182 people infected, 29 died. A bacterium that would later be
named L pneumophila was isolated from different organ tissues of guinea
pigs inoculated with lung tissue samples from 4 fatal cases. Several
problems were encountered when researchers first tried to classify this
outbreak. First, the bacteria are difficult to culture. It would not grow on
standard media, and a buffered charcoal yeast extract agar was
developed to culture it. Also, characterization was hindered due to the
lack of person to person contraction. The source was not known since
none of the affected persons had symptoms prior to arriving at the hotel.
It was later discovered that Legionella is water-born and was actually
aerosolized in the air-conditioning system.
8. Describe 5 methods for laboratory diagnosis of legionellosis and discuss the
advantages and disadvantages of each. (p. 394)
1. microscopy: direct fluorescent antibody (DFA) test. Fluorescein labeled
antibody against legionella. Low sensitivity
2. buffered charcoal yeast extract agar: most sensitive method
3. urinary antigen test: high sensitivity for L. pneumophila but low for other
species. Antigens persist in the urine of infected people, lasting up to 2
months.
4.nucleic acid amplification: highly specific and sensitive. Good for
respiratory secretions. May cause false-negatives
5. indirect fluorescent antibody: increase in titer may be detected in up to
40% of patients in the first week of disease, but it may take 6 months for
some. High titers can persist and cannot be used as an indication of
active infection. Poor sensitivity.
9. What are the consequences of having the smallest genome of any known freeliving human pathogen on laboratory diagnosis of Mycoplasma genitalium
infections? (lecture outline)
The small genome of M. genitalium requires an enriched medium (SP4
agar) and a lot of time in order to grow in a laboratory. As a result, PCR
and serology (for IgM) are used more commonly to identify the presence
of the bug.
D. Spirochetes and Rickettsiae
1. Explain the differences between obligate intracellular bacteria and facultative
intracellular bacteria and give examples of each. (lecture outline)
Obligate intracellular bacteria cannot make their own ATP and rely on the
host machinery. They frequently cause chronic disease. Example:
Rickettsiae and Chlamydiae
Facultative intracellular bacteria have developed the ability to survive and
grow within professional phagocytes frequently giving rise to chronic
and/or chronic disease. Example: tuberculosis, Salmonella typhimurium,
Listeria monocytogenes.
2. Describe the life cycle of Borrelia burgdorferi, the agent of Lyme disease.
(lecture outline)
For Lyme disease to exist in an area, at least three closely interrelated
elements must be present in nature: the Lyme disease bacteria, Borrelia
burgdorferi, ticks that can transmit them, and mammals (such as mice and
deer) to provide food for the ticks in their various life stages. The tick life
cycle consists of three distinctive stages: larvae, nymphs, and adults. A
blood meal is required for ticks to molt from the larvae stage to the nymph
stage and from the nymph stage to the adult stage. The tick larvae and
nymphs typically become infected with Borrelia burgdorferi when they feed
on infected small animals, particularly the white-footed mouse. The
bacteria remain in the tick as it changes from larva to nymph or from
nymph to adult. Infected nymphs and adult ticks then bite and transmit
Borrelia burgdorferi to other small rodents, other animals, and humans, all
in the course of their normal feeding behavior. Adult ticks preferentially
feed on the white-tailed deer, which thereby becomes an important
reservoir in regions of infestation. The tick life cycle takes two years to
complete.
3. Does Lyme Disease occur endemically in Alabama? Explain the reason for
your answer. (lecture outline)
No, Lyme disease does not occur endemically in Alabama because it’s
transmitted by Ixodes ticks, which are not native to Alabama.
4. Explain why laboratory diagnosis of Lyme Disease is complex and difficult. (p.
436)
B. burgdorferi are present in very small amounts in clinical specimens
from tissues and body fluids of patients, so microscopic examination and
even nuceic acid amplification have low sensitivity. Cultures are rarely
done because media is NOT readily available and organisms grow slowly
on them.
5. What is the difference between a “non-treponemal test” and a “treponemal
test” and how can each be used most effectively in diagnosis of syphilis? (p. 431432)
Non-treponemal tests (eg: VDRL or RPR) are biologically nonspecific and
they measure IgG and IgM antibodies developed against lipids released
from damaged cells during the early stage of disease and present on the
cell surface of treponemes. Positive reactions with these tests develop
late during the first phase of disease; the findings are negative in many
patients who initially have chancres. However, serological results are
positive within 3 months in all patients and stay positive in untreated
patients with secondary syphilis. Successful treatment of primary or
secondary syphilis leads to reduced titers measured in the nontreponemal
tests and thus can be used to monitor the effectiveness of therapy.
Treponemal tests: Treponemal tests are specific antibody tests used to
confirm a positive reaction with the VDRL or RPR test. Results of these
tests usually remain positive for the life of the person who has syphilis.
These tests are influenced less by therapy than the nontreponemal tests
6. Explain how the life cycle of Rickettsia rickettsii is responsible for clinical
manifestations of Rocky Mountain Spotted Fever. (lecture outline)
Rickettsia rickettsii are carried in the fluids of arthropods like ticks. When
the tick bites you, the bacteria will invade the endothelium. The organisms
multiply in the endothelium of small vessels causing inflammation, which
leads to vasculitis. The cells swell, become necrotic and thrombose the
vessel, leaving a bruised looking spot at the site of infection. This is the
rash that spreads with RMSF.
7. Describe the procedures that are necessary in order to cultivate rickettsiae in
vitro and explain whether or not this is a worthwhile method for diagnosis of
rickettsial diseases.(p. 452)
Rickettsiae will grow in tissue culture or embryonated eggs. They require
a culture to grow in because they are obligate intracellular bacteria. They
are hazardous to work with (infectious) so they are typically diagnosed
using microscopy, serological procedures (Ab presence) and PCR.
8. Describe 3 different human diseases for which ticks are a vector.
Rocky Mt. Spotted Fever: Rickettsia rickettsii
Monocystic ehrlichiosis: Ehrlichia chafeensis
Granulocytic ehrlichiosis: Anaplasma phagocytophilum
Lyme Disease: Borrelia burgdorferi
F. Neisseriae and Chlamydiae
1. Describe the unique life cycle of chlamydiae and the roles of the elementary
body and reticulate body in infectivity. (lecture outline)
Chlamydia is an obligate intracellular organism (it doesn’t have the ability
to make its own ATP)
Life Cycle:
1. infectious elementary body taken up into cytoplasm of host
cell>>>grows and becomes metabolically active inside of phagosome
2. transformational change of elementary body to reticulate body
3. reticulate body grows and forms more elementary bodies
4. reticulate body condenses back to elementary body
5. elementary bodes released from cell to infect other cells.
Reticulate body: replicating form of Chlamydia trachomatis; non-infectious,
but makes more elementary bodies which are infectious
2. Give an explanation for the failure to develop an effective vaccine against
Neisseria gonorrhoeae. (p. 319)
There is high antigenic diversity/variation in the variable region of the pilin
protein, to which antibodies are made. Antibodies against this region
protect against a homologous strain, but not a heterologous strain. This
results in no permanent immunity following infection and the failure to
develop an effective vaccine.
3. Describe the diagnostic method of choice for chlamydial urogenital infections
and explain why it is preferred over other methods. (p. 469)
Nucleic acid amplification tests (NAATs) are highly sensitive, very specific
and can be done using voided urine from a patient with urethritis. Car
must be taken to avoid contamination and inhibitors (urine). Cell staining
is insensitive, culture can be easily contaminated and has low sensitivity
and antigen detection assays are unreliable.
G. Mycobacteria
1. How do the methods of laboratory diagnosis for mycobacteria differ from those
used for the common gram-positive cocci? (p. 305-308)
1. Mycobacteria are detected by the acid-fast stain. Stain with
carbofuchsin or fluorescent dye, decolorize with acid-alcohol solution and
counterstain. The gram stain uses an acetone alcohol solution to
decolorize.
2. Specific species are identified with amplified nucleic acid probes.
3. Culture on solid agar, egg-based or broth-based media
4. Growth properties and colonial morphology
5. Definitive identification based on: production of niacin and reduction of
nitrate, characteristic cell wall lipids, species-specific molecular probes,
sequencing the 16S rRNA gene
2. Give a logical argument why the BCG vaccine is not used routinely in the
United States. (p. 301)
BCG immunization results in a positive skin test for prolonged periods,
making it more difficult to determine who has active infection. BCG is not
used in the USA because TB is rare. Vaccine is effective when given to
young children, but not in adults with latent infection. BCG cannot be
given to immunocompromised patients.
3. Is tuberculosis increasing or decreasing in the United States? Explain your
answer. (p 301; lecture outline)
Decreasing due to genetics and increased standard of living.
4. Explain why persons with HIV/AIDS are especially prone to develop disease
due to mycobacteria. (p. 301)
From book: The likelihood that infection will progress to active disease is a
function of both the infectious dose and the patient’s immune competence.
Active disease develops within one year in ~10% of patients with HIV and
a low CD4 count, compared to a 10% risk during the lifetime of a patient
that does not have HIV. In patients with HIV, disease appears before the
onset of other opportunistic infections, is twice as likely to spread to
extrapulmonary sites and can rapidly progress to death.
From other outline: Because of low immune system; However, the vaccine they
are given prevents the primary disease of TB, so stops the infection. But they are
a carrier and can transmit it to other people.
5. A 30 year-old dentist in apparent good health who is exposed to a patient with
tuberculosis develops a positive PPD skin test. Explain the most appropriate
course of action that should be taken.
First need positive skin test.
Prophylaxis regimen for exposure:
1. INH daily for 9 months (*this is the only one listed in the notes)
2. rifampin daily for 4 months
3. rifampin and pyrazinamide daily fro 2 months
Patients exposed to drug-resistant TB receive a longer course of
antibiotics.
6. Compare and contrast the pathogenesis and clinical manifestations of
tuberculoid and lepromatous leprosy. (lecture outline)
M. leprae: aka Hansen’s disease, humans and armadillos are natural host,
transmitted by inhalation or skin contact, incubation period is 3 months to
3 years
Diagnosis: does not grow on artificial media; AFB stain of nasal secretions;
lepromin skin test
Tuberculoid:
Non-progressive; intact cell-mediated response to M. leprae; organisms
rare in tissue; organisms grow in nerves and cooler parts of the body and
make granulomas; cutaneous loss of sensation from nerve damage due to
cell-mediated immunity
People lose body parts because they can’t feel them and they damage
them.
Lepromatous:
Depressed cell-mediated immunity response specific for M. leprae;
bacteremia with localization in nerves and skin; high number of organisms
in macrophages; loss of nerve function, leonine facies (low immune
response); other organs involved (testes, spleen, liver)