Download Normal flora

MCB 3020, Spring 2005
Host-Parasite Relationships
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Host-parasite relationships
I. Normal flora
II. Pathogenesis
III. Virulence
IV. Nonspecific host defenses
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I. Normal flora
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Organisms normally associated
with healthy body tissues.
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A. Skin
Not generally hospitable to microbes
relatively low pH (4 to 6)
often too dry
Normal flora
staphylococcus
corynebacterium
(eg. Propiobacterium acnes)
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B. Teeth
enamel
matrix
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gingival
crevice
tooth cross-section
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1. Plaque
Bacteria growing on the teeth
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2. Tooth decay (dental caries)
Breakdown of tooth enamel caused
by acids produced by plaque.
Penetration of the matrix of the tooth
by bacteria
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Acids, like lactic acid, are produced
during sugar fermentations
in anaerobic microenvironments.
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simulated plaques
Picture
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3. Plaque bacteria
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a. Streptococcus mutans
• colonizes tooth crevices
• produces dextran for attachment
• dextran is produced from
sucrose (table sugar)
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S. mutans
Picture
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b. Streptococcus sobrinus
colonizes smooth surfaces
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attaches to glycoproteins that coat
the tooth enamel
c. Heavy plaque has the anaerobe
Actinomyces (and others)
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C. Mucous membranes
1. Gastrointestinal tract
Stomach (pH ~2)
Lactobacilli
small intestine (pH 4-5)
Lactobacilli
Enterococci
large intestine (pH 7)
Enterococci
Picture
Bacteroides 23
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TB
Other gastrointestinal information:
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• normal flora can prevent pathogens
from colonizing
• antibiotics can sterilize the
gastrointestinal tract giving
opportunistic pathogens
a chance to colonize
2. Upper respiratory tract
staphylococci
streptococcus
pathogens
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(most are trapped in nasal secretions)
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3. Lower respiratory tract
(trachea, bronchi, lungs)
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very few organisms
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4. Urogenital tract
Bladder
few organisms
Urethra
E. coli
Proteus
Vagina
Lactobacillus acidophilus
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TB
II. Pathogenesis
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The process by which a pathogen
damages a host.
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A. Entry
1. Site of entry
Mucous membranes
through intact membranes
through breaks
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Skin
usually through breaks
insect bites
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2. Specificity for host
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Pathogens often adhere best to a
specific tissue of a specific host
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Tissue
specificity
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Host
specificity
Neisseria
urogenital
gonorrhoeae epithelium
Human
Salmonella
typhimurium
Mouse
intestinal
epithelium
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3. Adherence factors on microbes
Glycocalyx
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Adherence proteins
Lipoteichoic acids
Fimbriae
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B. Growth
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Factors affecting growth
physical conditions
nutrient availability
eg. iron
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C. Spread
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through the bloodstream
through the lymph system
through tissues
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D. Virulence factors
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extracellular proteins produced by
pathogens to aid in establishment
or maintenance of disease
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D. Virulence factors
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hyaluronidase
collagenase
streptokinase
(breaks down fibrin clots in blood)
coagulase (promotes clotting)
hemolysins (attack cell membranes)
leukocidins (lyse white blood cells)
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E. Exotoxins
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Proteins excreted from the pathogen
that harm the host
can travel through the body
TB
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1. Diphtheria toxin
Corynebacterium diphtheriae
protein
encoded by lysogenized phage beta
blocks eukaryotic protein synthesis
through ADP-ribosylation
of EF-2 (elongation factor-2)
potent: one molecule can kill one cell
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2. Tetanus toxin
Clostridium tetani
deep puncture wounds
protein: neurotoxin
blocks muscle relaxation
twitching paralysis
lockjaw
TB
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Picture
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3. Botulinum toxin
Clostridium botulinum
grows in improperly preserved food
protein: neurotoxin
blocks muscle contraction
flaccid paralysis
most poisonous substance known
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4. Cholera toxin
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Vibrio cholera (water contamination)
protein
enterotoxin (small intestine)
activates adenyl cyclase
causes diarrhea
intestinal cell
Na+
lumen
H2O
Na+
Cl
H2O
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bloodstream
cholera toxin
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F. Endotoxins
Gram lipopolysaccharides
Escherichia
Salmonella
Shigella
fever and diarrhea
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TB
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exotoxins
endotoxins
highly toxic
weakly toxic
nonpyrogenic
pyrogenic
(fever-causing)
highly
immunogenic
weakly
immunogenic
TB
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III. Virulence
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The capacity to cause harm
A. Invasiveness
The capacity to cause harm
by entry and spread
B. Toxigenicity
The capacity to cause harm
by toxic effects
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Clostridium tetani
low invasiveness
high toxigenicity
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Streptococcus pneumonia
high invasiveness
low toxigenicity
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C. Measurement of virulence
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LD50
Dose (number of cells/animal) that
kills 50% of animals infected
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D. Salmonella virulence factors
cytotoxin
LPS
Inhibits host prot. synth.
virulence
plasmid
fimbriae
O-antigen
flagellum
enterotoxin
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IV. Nonspecific host defenses
A. Anatomical defenses
B. Inflammation
C. Fever
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A. Anatomical defenses
Lysozyme
In tears and other secretions
skin-physical barrier
stomach-low pH
cilia
normal flora
flushing of the urinary tract
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TB
B. Inflammation
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swelling and redness
results from complement activation
and phagocytic attack
localizes noxious agent
often by producing a fibrin clot
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C. Effects of fever
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low fever
often accelerates immune response
high fever
often favors the pathogen
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Study objectives
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1. Know that normal flora are organisms normally associated with healthy body
tissue. Normal flora are often beneficial. However, under certain conditions18
normal flora can invade and cause disease.
2. Memorize the names of bacterial normal flora adapted to survive in certain
regions of the body.
3. Know what plaque is and how it can lead to tooth decay.
4. Understand the basic steps of pathogenesis.
5. Know that the following are adherence factors: glycocalyx, adherence proteins,
lipoteichoic acid, fimbriae.
Continued
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6. Know how the following invasion enzymes work:
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a. hyaluronidase breaks down hyaluronic acid, a polysaccharide that cements
tissues together
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b. collagenase breaks down the fibrous protein collagen, which normally
supports tissues
c. streptokinase breaks down fibrin clots. Hosts sometimes form fibrin clots
to wall off the invader.
d. coagulase is a fibrin-clotting enzyme may offer protection against
host defenses
e. hemolysins, usually lipases, breakdown the lipids, and thereby lyse cells
f. leukocidins lyse white blood cells impairing host defenses that rely on
defenses mediated by these cells.
7. Know the details about the following exotoxins: tetanus toxin, botulism toxin,
and enterotoxins (cholera toxin)
8. Know that endotoxin is lipopolysaccharide and be able to compare
and contrast endo- and exotoxins.
9. Know how toxigenicity and virulence contribute to disease.
10. Know the Salmonella virulence factors.
11. Understand the nonspecific host defenses: anatomical, inflammation, fever.