Download I. Microbes

Medical
Chapter 1
Microbiology
Introduction
I.
Microbes
1. Definition (microorganism): are the little and simple organisms with rapid
growth rates.
2. Classification:
1) Non—cellular type
Such as: viruses
General Characteristics of Viruses :
1. Smallest: 20 – 300 nm, most were too small to be seen with the light
microscope , filtrable.
2. Simplest: non-cellular entity, contain DNA or RNA and protein.
3. Obligate intracellular parasites (专性细胞内寄生): growing only within the
living cells.
4. Self-replication (自我复制): Once it has invaded a cell it is able to direct the
host cell machinery to synthesize new intact infectious virus particles (virions).
Definition of a virus:
2) Prokaryotic type
No nuclear membrane or mitotic apparatus, only nuclear region can be seen,
which composed of DNA.
No separate internal membrane bound organelles .
Such as: Archaebacterium(古细菌):
Eubacterium（真细菌）:
Bacterium
Mycoplusma
Chlamydia
Riclcettsia
Spirochetes
Actinomycetes
Cynaobacterium(蓝细菌)：no pathogenesis to human
3) Eukaryotic type
intracellular membrane —enclosed organelles,
nucleus : two membrane layers
Endoplasmic Reticulum (ER): rough ER ;Smooth ER
Mitochondria
Such as Fungi : hyphae and yeast
3. Distribution of Microorganisms:
1) In environments.
2) In human organisms
II Microbiology and Virology
1. research objective : Pathogenic Microbes
1)biological properties
2)pathogenesis and immune response
3) Diagnosis
4)therapy and protection
Microbiology:
Virology：is the study of viruses, complexes of nucleic acids and proteins that have
the capacity for replication in animal, plant and bacterial cells.
2. History
Leeuwenhock:
invent Microscope in 1674 .
Pasteur
:
pasteurization , Vaccine
Koch
:
solid medium, purify bacteria
Pathogenic microbe criterion
Lister
:
disinfection aseptic technique
Iwanovsky :
virus.
3. Modern Microbiology
1) Most bacteria were controled by antibiotics. Drug-resistant strains—>
resistence plasmid.
2) Normal flora—opportunistic pathogens
(flora disequilibrium super-infection )
Hospital acquired infections.
New bacteria : Helicobacter pylori—chronic gastritis.
3) Viral researches have made progress.
New presented viruses: AIDS
New diagnostic techniques . ELISA; PCR( polymerase chain reaction.)
Viral infection associated with tumors:
mechanisms of Viral disease;
anti-infection immunology and develop vaccines:
Research tools of molecular biology:
anti-virus drugs:
4) New type vaccine .
Microbial genomic program, MGP .
Basic Principles of Microbiology
Chapter 2
Basic Properties of microbes
Section I
Bacteria
I . Size and Shape of bacteria
(I ) Size of bacteria
Measure unit: um(micrometer): Coccus 1 um
(II) Shape of bacteria
1. coccus (cocci)
1) diplococcus : in pairs
2) streptococcus: long chain
3) tetrad and sarcina:
bacillus
2—3um
4) staphylococcus: irregular cluster
2. bacillus (bacilli): rod
3. Spirilla bacterium
1)vihrio
v. cholera
2)Spirillum Helicobacter H. pylori
II. Basic Bacterial Structure
cell wall
Basic structure
cell membrane, mesosome
Cytoplasm: ribosome, plasmid, cytoplasmic granules;
nucletid
（I）cell wall
1. function :
1)protection
2) keep the constant shape .
3)antigenicity .
4) exchange material
2. structure and chemical composition: peptidoglycan（mucopeptide）
1)polysaccharide
backbone: N-acetyl glucosamine link N-acetyl muramic acid with 1.4 –glucosidic
bond
2)tetrapeptide side chain: link muramic acid. ala glu lys ala
3)pentaptide bridge: G+ : L—glycine; G－ : diaminopimelic acid
3. Special components of Gram-positive cell wall
(1) eichoic acids : wall teichoic acid and membrane teichoic acid
functions :
1) bind Mg2+(magnesium)
upply of this ion to the cell
2) provide the cell with its consistency
3) adhesion ------pathogenicity
4) antigenicity
(2) polysaccharides
may contain a variety of sugars.
4. Special components of Gram-Negative cell wall .
(1) peptidoglycan
(2) Outer membrane : exchange receptor(sex pili phaqe)
1) Lipoprotein
are firmly but non covalently attached to the peptido-glycan and out
membrane
2) lipopolysaccharide, LPS
a complex and unique glycolipid consisting of three distinct but
covalently linked regions:
a) lipid A: glucosamine disaccharide units connected by pyrophosphate
bridge .
endotoxin , non-genus specific
b) core polysaccharide
c) specific polysaccharide “O” Ag
（II）Cell membrane
mesosome : invaginated vesicular membrane，to increase membrane area such as
chondriosome(线粒体) and spindle.
Function as 1) spindle-like（类纺锤体）：cell division
2) chondroid(类线粒体)：
（III）Cytoplasm
plasmid ： extra-chromosomal genetic material, circle double streands DNA, to
replicate independently, to carry genetic information, to control a wide rang of
functions to bacteria.
（Fertility）factor F ---------control sex pili
factor R----------control drug resistance
col factor ------control E col: to produce bacteriocin.
III.
Special structure of bacteria
Specific structure: capsule, flagellum, pillus, endospore
（I）capsule
1. Concept: bacteria secrete a slime layer outside the cell wall, which is composed of
polysacchride or polypeptid.
Such as :pneumococcus, anthracis
>0.2um
capsule
<0.2um microcapsule
slime layer
Washed off
does not appear to be associated with the cell.
2. Functions： condition , enviroment host body
1. anti—phagocytosis
surface
phagocytosis
.opsonic phagocytosis
2. anti-dry
3. adherence （粘附作用）
（II）flagella
1. Concept: long filamentous appendage.
Originate: in the protoplasmic membrane,
2. Functions:
1). motility
2). antigenicity “H”-Ag , some bacterin
3). pathogenicity and adherence:
（III）pili （pilus）
1. Concept: filamentous appendage on the surface of bacteria, shorter straighter, and
thinner than flagella.
2. Classification
1). common pili 100—200/cell
adherence organ of bacteria, adhere to the surface of mucosal membrance ,be
associated with pathogenicity.
2) sex pili 1—4/cell, male bacteria with sex pili, to transfer of genetic material
（DNA）during bacteria conjugation
F+———F－
(IV) spore
1. Concept: round or elliptic minute (微小的) body formed inside the bacteria
—endospore
dormant form （resting forms）：spore
vegetative form
: bacteria
2. Functions: highly resistant to heat . chemical .dry.
reasons: （1）many layers .thick coat
（2）little water. 40% free water
（3）large amount of calcium dipicolinate
（4）heat-stable enzyme （DPA,吡啶二羧酸钙）
destroy spore: autoclave, under 121°C 1.05kg/cm2 for 15—30′
3. forming: inadequate nutrition
IV Special living form of bacteria.
Bacterial L—Forms: cell wall deficient form
Some bacteria's form of small filterable protoplasmic elements with defective or
absent cell walls.
1) Morphology: spherical body, pleomorphic and plastic.
Colonies: fried egg
2) Media . high osmotic , reversion
3) Pathogenicity:
Similar to the infection of virus or mycoplasma （organisms without wall）
Infiltration of mononuclear cells and lymphocytes and different from that of the
bacterial infections , with mainly infiltration of neutrophils.
V Bacterial metabolism
Metabolic products
1. Catabolic products and biochemical reaction
Catabolism refers to chemical reactions that result in the breakdown of more
complex organic molecules into simpler substances,which can be used as mark to
identify the class of the bacteria.
2. Anabolic products and clinical significance
1) pyrogen
polysaccharide of G－ cell wall(LPS) that cause a rise in temperature in an animal or
human body is called pyrogen .
anti-high temperature 121°C, 30’. Cause fluid infusion reaction,
2) toxin and invasive enzymes
exotoxin
endotoxin
enzyme
3) pigment
water—soluble P. aerogenosa ---green
fat ---soluble
S. aureus —golden
4) antibiotics
Killing or inhibiting substances produced by some kinds of microorganisms, such as
Actinomycete.
5) bacteriocin
protein by certain bacteria, which can kill or inhibit the growth of related strains.
VI. Bacterial multiplication
1. nutrient material
(1) water （2）carbon source : energy（3）Nitrogen source
constituent
protein（4）inorganic ions (5)growth
2. nutrient type 1)autotrophy 2)heterotroph
saprophyte; parasite
3. Bacterial growth and reproduction
growth condition: (1)enough nutrients (2) Suitable PH (3) suitable temperature
(4)suitable air
obligate
aerobe
obligate anaerobe
facultative anaerobe
microaerophilic bacterium
Reasons that obligate anaerobes can’t grow in free oxygen condition:
(1) Lack of cytochrome and cytochromase----Eh 300mv/120mv
(2) lack of superoxide dismutase (SOD) catalase, peroxidase.[O2－] H2O.
4. mode and spead of B. reproduction
1)Mode:
binary flssion. chromosome replication . synthesize cell membrane and
wall G+B chromosome bind mesosome G－B. chromosome bind membrane.
2)speed: generation time 20---30min
For example: E. coli ; Myco. Tuberculosis: 18 hrs
3) growth curve:
The schematic growth curve refers to a single bacterial culture, introduced into and
growing in a fixed volume with a fixed (limited) amount of nutrient.
a. lag phase; adaptation
Bacteria are becoming "acclimated" to the new environmental conditions to which
they have been introduced (pH, temperature, nutrients, etc.). There is no significant
increase in numbers with time.
b. logarithmic phase/ Exponential Growth Phase: most rapid reproduction
The living bacteria population increases rapidly with time at an exponential growth in
numbers, and the growth rate increasing with time. Conditions are optimal for growth.
c. stationary phase: rate of reproduction = rate of deed
With the exhaustion of nutrients and build-up of waste and secondary metabolic
products, the growth rate has slowed to the point where the growth rate equals the
death rate. Effectively, there is no net growth in the bacteria population.
d. decline phase: the rate of dead > the rate of reproduction.
The living bacteria population decreases with time, due to a lack of nutrients and toxic
metabolic by-products.
Section II
Viruses
I． Size and Shape
Virion（病毒体）: The basic infectious particle of a virus is known as the
virion.The virion is composed of the nucleic acid genome, structural protein and
in some viruses an enclosing lipid-containing envelope.
Size :
20 -- 300 nm ( the most virus く 150 nm);
Shape: the commonest shape ---- small spherical virus
Others-----filamentous,brick,bullet
II. Structure and Chemical Composition
Viruses contain:
a nucleic acid genome (RNA or DNA)
a protective protein coat (called the capsid)
A Viral envelope
Non-structural protein
(I) Core : Nucleic acid（核酸）
1. Single kind: consist of DNA or RNA ( never both).
1) DNA :
single-stranded DNA (ssDNA):
double-stranded DNA ( dsDNA ) : --- the commonest type of nucleic acid in
viruses of human.
2) RNA:
double-stranded RNA (dsRNA) :
single-stranded RNA (ssRNA): --- the commonest type of nucleic acid in viruses
of human..
＋ssRNA : is the same as the viral mRNA ,can direct as viral mRNA
-ssRNA: as a template transcribe complementary mRNA.
Retrovirus: ＋ssRNA
2. Functions:
1) virus replication: template
2) genome （基因组）: encodes genetic information.
3) infectious nucleic acid（感染性核酸）: refer to some viral nucleic acid which
can enter cells and reproduce new viruses,such as dsDNA V and +ssRNA V.
*segment of RNA (分节段 RNA)
*open reading frame, ORF(开放读码框)
3. Non-structural protein:
(1) viral enzymes:
such as ： RNA-dependent RNA polymerase or
transcriptase .
(2) specific viral protein: such as : transformation protein of tumor virus.
(II) . Capsid （衣壳）： protein coat ,
1. capsid is composed of distinct morphologic units---- capsomeres（壳粒）
--- icosahedral symmetry:
--- helical symmetry:
--- complex symmetry:
2. Functions:
1) protection (protect viral nucleic acid from enzymic action).
2) specific binding sites.
3) antigenicity of capsid protein.
(III). Envelope (包膜): lipid, glycoprotein
1. Consists of lipid bilayer and glycoprotein:
lipid --- derived from host cell membrane.
Glycoprotein--- coded by the viral genome.
Spikes(刺突) --- virus-encoded glycoprotein protruding from lipid bilayer,
which are important for adsorption and entry into the host cell.
2. Functions:
1) as the binding sites(for enveloped virus).
2) antigenicity of glycoprotein.
III. Viral Multiplication
Replication: The process of intracellular viral multiplication, consisting of the
synthesis of PROTEINS; NUCLEIC ACIDS; and sometimes LIPIDS, and their
assembly into a new infectious particle.
(I.) Replication cycle（复制周期）:
1. adsorption (吸附):
interaction between specific binding sites on viral capsid (or envelope) and
specific receptors on host cell surface.
2. penetration（穿入）:virus enter the cells.
Entry of Naked viruses: endocytosis
Entry of enveloped virus :
(1) simple fusion of membranes --expels nucleocapsid into cytoplasm
(2) entire particle taken up by endocytosis-- virus still in vesicle which fuses with
endosome (due to low pH)
3. uncoating（脱壳）：
Rapid change from stable structure to release of genome
--depends on virus structure and presence of envelope
--during which the endocytic vesicle and the viral capsid are enzymatically
degraded and the viral genome is released.
4. biosynthesis（生物合成）:
4.1 Three kinds of strategies for RNA viruses:
(1)Positive-strand viruses
a. SYNTHESIS OF VIRAL PROTEINS
The mRNA is translated into a single polypeptide (polyprotein), which is cleaved.
Products of cleavage include: An RNA polymerase (replicase)、Structural components
of the virion、Proteases .
b. RNA REPLICATION
1. Viral RNA polymerase copies plus-sense genomic RNA into complementary
minus-sense RNA:
2. New minus sense strands serve as template for new plus sense strands.
3. New plus strand has three alternative fates:
i. It may serve as a template for more minus strands
ii. It may be packaged into progeny virions
iii. It may be translated into polyprotein (In this case VPg is removed prior to
translation)
(2) Negative-strand viruses
a. TRANSCRIPTION
to refer to synthesis of mRNAs.
b. TRANSLATION
Messenger RNAs are translated on host ribosomes and all five viral proteins made at
the same time.
c. RNA REPLICATION
RNA replication is the process by which new copies of genome-length RNAs are
made .
RNA replication occurs in the cytoplasm and is carried out by the viral RNA
polymerase. The new positive strand is copied into full length minus strand.
d. New negative strands may:
i. be used as templates for the synthesis of more full length plus strands
ii. be used as templates for the synthesis of more mRNAs
iii. be packaged into virions
(3).Retroviruses
4.2 DNA viruses:
(1) Early gene expression:--------early phase
The early transcript (primary transcript) results in the mRNAs for early proteins. The
mRNAs are translated in the cytoplasm.
(2) DNA replication
DNA replication uses host cell DNA polymerase, which recognizes the viral origin of
replication. This process of DNA replication is very similar to that which occurs in the
host cell .
(3) Late gene expression------late phase
Late mRNAs are made after DNA replication.
5. assembly and release（装配和释放）：
--- by lysis of the host cell ( naked viruses).
--- by budding through cell membrane (enveloped viruses).
Not all released viral particles are infectious. The ratio of non-infectious to
infectious particles varies with the virus and the growth conditions.
(II.) Unnormal multiplication:
1. Abortive infection: When a virus infects a cell (non-permissive cell), but
cannot complete the full replication cycle, i.e. a non-productive infection.
2. Defective virus（缺陷病毒）: a defective virus is one that lacks one or more
functional genes required for virus replication. defective virus require helper
activity from another virus for some step in replication.
3. Interference（干扰现象）：The infection of cell by a virus results in that cell
becoming resistant to infection by other viruses.
IV. UNCONVENTIONAL AGENTS
Subvirus : refer to the kind of infectious factor which is smaller than virus.
1. viroid(类病毒) and virusoid(拟病毒)：
--To contain RNA only
--They are small (less than 400 nucleotides), single stranded, circular RNAs
--The RNAs are not packaged, do not appear to code for any proteins
--To have only been shown to be associated with plant disease.
2. prion (朊病毒，朊粒)：
only protein(prion protein, PrP) cause animal and human central nervous system
disease.
Concepts
1. Prions - short for proteinaceous infectious particle.
Prion(朊病毒，朊粒): infectious agents consisting only of protein, with no nucleic
acids and ,which are responsible for a number of transmissible spongiform
encephalopathy (TSEs) in animals and human.
2. PrP(朊蛋白): This protein is encoded by normal cellular gene and found in the
membranes of normal cells (its precise function is not known), but can altere its
conformation to distinguish the infectious agent(prion). The normal one is called
PrPC(cellular PrP,细胞朊蛋白), while the infectious one is called PrPSC (scrapie
prion protine,羊瘙痒病朊蛋白).
Section III
Medical
Mycology
The fungi--being eucaryotic organisms, lack chlorphyll, nonmotile, grow as single
cell or as long dranched, filamentous strcture
I.
morphology
1. monocellular fungi:
(1) yeast form;
(2) yeast-like form
2. multicellular fungi:
(1) hypha—A hypha is a long, branching filament that collectively form the feeding
structure of a fungus called the mycelium（菌丝体）.
(2) spore —Spores are dispersal（散播） units of fungi.
II.
culture properties
1. multiplication modes:
(1) Budding（芽生）
2. sabouraud medium：Dextrose, peptone, agar, pH 5.6
3. monocellular fungi---37℃;
4. grow slowly:
multicellular fungi---28℃
4 days-3 weeks
yeast-form colony
6.
colonal types
yeast-like colony
hyphomycete-form colony
Chapter 3 Infection
Section I
Bacterial Infection
Virulence refers to extent of pathogencity.
Medium lethal dose, LD50: The number of pathogens required to cause lethal disease
in half of the exposed hosts is called an LD50.
Medium infective dose , ID50: The number of pathogens required to cause disease (or,
at least, infection) in half of the exposed hosts is called the ID50
I. Bacterial Pathogenesis mechanism
(I) Invasiveness
The ability of B .to resist host defence, colonize, multiply and spread.
1. adhesion
Bacterial infections are usually initiated by adherence of the microbe to a specific
epithelial surface of the host. For bacterial pathogens, successful adherence is usually
a necessary prerequisite for virulence and even infection.
(1) microcolony / biomembrane
microcolony : bacterial microcolony formation is an event preceding mature biofilm
formation.
biomembrane(Biofilm): Biofilms are bacterial communities which are enclosed
within a matrix of polysaccharides produced by the bacteria and adhere to a living or
inert surface. In nature, biofilms constitute a protected growth modality that allows
the bacteria to survive in hostile environments.
(2) adhesive factor
1）pili, capsule, micro-capsule, terminal structure.
2) adhesin: colonization factor,
2. invasion ---invasion gene
invasion can refer to the ability of an organism to enter a cell, although in some
instances it can mean further passage into the systemic vasculature.
(1) Some bacterial pathogens reside on epithelial surfaces e.g. Vibrio cholerae.
(2) Other species are able to penetrate these barriers but remain locally.
(3) Others pass into the bloodstream or from there onto other systemic sites. This
often occurs in the intestine, urinary tract and respiratory tract, and much less
commonly through the skin.
3. Penetration and spread
(1) coagulase: S. aureus
fibrinogen
fibrin
surround bacteria
(2) hyaluronidase (spreading factor)
hydrolyze hyaluronic acid tissue loose, B. spreads,
(3) streptokinase. SK. Lyse fibrin
(4) streptodornase, SD, resolve DNA.
(II). toxin
1. Exotoxin
Exotoxins are proteins, often enzymes, produced inside of cells and which do their
damage (as with endotoxins) only upon release from the cell.
(1) excreted by living cells , mainly G+ B.
(2) polypeptide
(3) Heat-unstable, 60°C, 1-2hr destroy
(4) Strong antigenicity，exotoxin to make toxiod
A toxoid is a physically or chemically inactivated exotoxin.
(5) highly toxic
(6) high selection for tissues
a. neurotoxin：is an exotoxin that disrupts nerve cells.
tetanospasmin:
spinal cord
b. cytotoxin : is an exotoxin that disrupts host cells.
diphtherotoxin
c. enterotoxin: is an exotoxin that disrupts the lining of the gastrointestinal tract.
cholera toxin
(7) exotoxin subunit A： toxicity
subunitB: non-toxicity, bind receptor of sensitive cell
2.Endotoxin
(1) integral part of G－ B. Cell wall. .Liberated upon their disintegration.
(2) LPS, main toxic part: Lipid A
(3) Heat-stable: 160°C 2－4hr
(4) Can’t converted into toxiod
(5) Weakly toxic
(6) Non-specific Function:
all endotoxins produce the same symptoms.
(1) fever
(2) WBC reaction
S induce
neutrophi releasing factor WBC except S. typhi
LPS
blood platelet ,WBC,complement, kinin.
Vasoactive , substances,eg,
Serotonin, kallikrein. Kinins
micro- circulation failure
(3) Shwartzman phynominen and disseminated intravascular coagulation(DIC)
(4) endotoxemia and shock
II. Occurance and development of bacterial infection
(I) Origin of infection
1. Exogenous infection:
patient
carrier
2. Endogenous infection:
(II).The mode of infection
resp. tract
digestive tract
damaged skin or mucous membranes
arthropod vector
contact: sex contact(STD)
(III) The type and outcome of infection
1. inapparent infection
2. apparent infection
3.whole body infection
toxemia: is the presence of exotoxins in the blood.
pyemia: is caused by pyogenic microorganisms in the blood.
endotoxemia: is the presence of endotoxins in the blood.
septicemia: illness that occurs when poisonous substances (toxins) produced by
certain bacteria enter the bloodstream.
bacteremia: is an invasion of the bloodstream by bacteria.
4. Carrier state
Section II Viral Infection and Pathogenicity
I. Thepathogenesis mechanism of viral infection
(I). virus – cell interactions:
1. cytocidal effect 杀细胞感染
virus which infect and replicate within cells causing the cells to lyse when the progeny
virions are released.
2. steady state infection 稳定状态感染:
viruses are produced from the infected cells but the cells are not killed by the process.
--- integration of viral Ag in cell membranes.
--- cell fusion. Such as CMV
3. inclusion body
inclusion bodies：round, oval, or irregular-shaped bodies occurring in the cytoplasm
and nuclei of virus-infected cells, as in disease caused by filtrable virus infection such
as rabies, smallpox, herpes, etc; called also elementary b's and intranuclear inclusions.
4. cell apoptosis 细胞凋亡
Viruses have the potential to initiate or stay the onset of programmed cell death
through the manipulation of a variety of key apoptotic proteins of the host cell. Such
as HIV, adenovirus.
----- Cells that are induced to apoptosis:
------ shrink
------ have their mitochondria break down with the release of cytochrome c
------ develop bubble-like blebs on their surface
------ have the chromatin (DNA and protein) in their nucleus degraded ,and DNA
break into small, membrane-wrapped, fragments
5. integration 整合作用 and cell transformation 细胞转化:
integration: integration of the viral genome into cellular DNA .
cell transformation: "the introduction of inheritable changes in a cell causing
changes in the growth phenotype and immortalization".
oncogenic virus --- induces cell transformation
The oncogenic virus associated with human tumors:
HBV--- hepatocellular carcinoma
HPV --- cervical carcinoma
EBV --- Burkitt lymphoma , nasopharyngeal carcinoma
HSV-2 --- cervical carcinoma
HTLV --- T cell leukemia
II. virus – immune system interaction:
1. immunopathological reactions:
2. the injury of immune system induced by virus infection:
III. The pathways of viral infections
1. horizontal transmission: (水平传播):
Viruses transmission from Person -to-person:
The most common STDs are listed below:
Gonorrhea.
Chlamydia.
Syphilis.
Trichomonas.
Human papillomavirus (HPV).
Genital herpes.
Hepatitis B and Hepatitis C.
Human Immunodeficiency Virus (HIV).
2 . vertical transmission（垂直传播）:
Viruses transmission from mother to infants or child :
--- through placenta ( congenital infection, congenital deformity 先天性畸形)
--- through birth canal (infection of newborn 新生儿感染)
--- through Breast Milk from virus-infected mothers
The viruses which can result in congenital infection :
1)rubella virus 风疹病毒
2)cytomegalovirus(CMV) 巨细胞病毒
3)herpes simplex virus-II(HSV-II)单纯疱疹病毒-II 型
4)hepatitis B virus(HBV)乙肝病毒
5)human immunodeficiency virus (HIV)人类免疫缺陷病毒
III. The type of viral infection
1. inapparent or subclinical infection
viruses enter the body ,but cause no apparent clinic syndrome
2. apparent infection or infectious disease.
viruses enter the body ,which can cause apparent clinic syndrome
(1) acute viral infection: viruses exist in the bodies for a short time (not＞6 monthes)
(2). persistent viral infection: viruses exist in the bodies for a long time (＞6 monthes)
1) chronic infection: virus can be continuously detected.
2) latent infection 潜伏感染: virus is usually not detectable but patient may have
periodic out-breaks of disease.
3) slow virus infection 慢发病毒感染: with long incubation periods(years), subacute
progressive, caused by lentivirus(HIV) , Measles virus (SSPE)or unconventional virus
( prion)。
4) delayed complication after acute viral infection.
Subacute Sclerosing Panencephalitis (SSPE): is a late manifestation of measles
virus infection, developing usually 6 and 12 years after natural measles infection to
cause a serious viral encephalitis of children and young adults.
Section III
Pathogenisis of fungi
1. superficial mycoses (Dermatophytes)
infect skin, nail and hair --- cause tinea
*pathogenic fungi infection----exogenous infection
2.*opportunity fungi infection----endogenous infection
flora disquilibrium--Candida
albicans : mucocutaneous infection ---- thrush
Pneumocystis carinii is an opportunistic fungal pathogen causing P. carinii
pneumonia (PCP). PCP continues to be a major cause of morbidity and mortality in
patients with AIDS despite the availability of prophylaxis and improved antiretroviral
therapy.
3. deep mycoses----chromic granulama, tissue ulcer , necrosis
Organ infection ----meningitis
4. *fungal poisoning ----Fusarium; Arthrinium; Patulin; Flavus
*fungal toxin can cause cancer:
aflatoxin---10g/d/personcancer
5. *hypersensitive disease
penicillium;
fuarium;
aspergillus---asthma; urticaria; allergic rhinitis; allergic
dermatitis
Chapter 4.
Immunity against microbe infection
Section I
Anti-infection Immunity
I. Non-specific or innate immunity.
1. Anatomical barriers
(1) Skin and mucosa
Skin and mucous membranes
Acid pH
Fatty acids
Hydrolytic enzymes (lysozyme)
Proteolytic enzyems and bile
2. Phagocytic cells
Phagocytosis is a process describing the engulfment and destruction of
extracellularly-derived materials by phagocytic cells, such as macrophages and
neutrophils. Five steps of phagocytosis are illustrated in the image below.
(1) Schematic diagram of the steps in phagocytosis:
a. Attachment of the bacterium to the long membrane evaginations, called
pseudopodia.
b. Ingestion of the bacterium forming a "phagosome," which moves toward the
lysosome.
c. Fusion of the lysosome and phagosome, releasing lysosomal enzymes into the
phagosome.
d. Digestion of the ingested material.
(2) Results of Phagocytosis
a. complete phaged
The lysosomes fuse with the phagosomes containing the ingested microbes and the
microbes are destroyed
b. un-completed phaged
Some bacteria, such as Legionella pneumophilia (inf) and Mycobacterium species
(inf), are more resistant to phagocytic destruction once engulfed.
3. NK cells
Role in early viral infection or tumorogenesis before activation of acquired immunity.
4. Secretory molecules
Complement system – 20 proteins in a controlled enzymatic cascade which targets the
membrane of pathogenic organisms and targets theme for destruction
Interferons – proteins made by cells in response to virus infection that induced a
generalized antiviral state in surrounding cells
II. Specific or adaptive immunity.
1. humora immunity
2. cell-mediated immunity
Section II
Immunity against bacteria
I. anti- extracellular bacteria
1. Phagocytic cells: Neutrophils (PMN) and macrophages and monocytes are the
most important cellular components of the non-specific immune system.
2. antibody and complement
3. cell mediated immune response
II. anti- extracellular bacteria
1. Phagocytic cells: Neutrophils (PMN) and macrophages and monocytes are the
most important cellular components of the non-specific immune system.
2. cell mediated immune response
3. mucosa immunity: IgA is the major class of Ig in secretions - tears, saliva,
colostrum, mucus. Since it is found in secretions secretory IgA is important in local
(mucosal) immunity.
Section III
Immunity against virus
I . Non-specific immunity:
A. Inherent Barriers
Skin, Mucus, Ciliated epithelium , Low pH
B. NK cell
C. Humoral and cellular components
（1）. Interferon (IFN)
（2）. Complement
（3）. Cytokines
TNF-a, IL-1 and IL-6
Interferon (IFN)
1. concept: a class of protein(glycoprotein) produced by cells in response to viral
infection or other interferon inducers that protected other cells of same species from
attack by a wide range of viruses.
2.classification of IFNs:
Gene
cell
anti-viral activity
Modify-immune
responses
IFN-α
chromosome 9
blood mononuclear
cell
+++
++
IFN-β
chromosome 9
fibroblasts
+++
++
IFN-γ
chromosome 12
Ag-activated T
cell
++
+++
3.
production of IFN:
(1) interferon inducers: eg. PolyI:C(poly inosinic:poly cytidylic acid), viruses and
bacterial endotoxins, etc
(2) Mechanism :
IFN inducer acts on cell receptors --- IFN gene activation--- transcribe IFN mRNA--IFN synthesis--- IFN released
4.
antiviral activity:
not act directly on virus, but through induction of antiviral proteins(AVP).
(1) Mechanisms:
IFN combines with specific receptor on cell surface ---AVP gene actived --- AVP
mRNA transcribed---AVP synthesis
AVP consists of : protein kinase
2,5-A synthetase
(2) Characteristics :
----not act directly on virus .
----broad-spectrum antiviral activity.
----host species specific: inhibit viral replication only in the species in which it was
produced.
5.
other activities:
(1) anti-cancer
(2) Modify immune responses
----NK activation
----macrophage activation
----Increased expression of MHC molecules
II. Specific immunity
1.
Humoral immunity
1) Neutrilizing antibody: blocking the virus replication from binding and gaining
entry to the host cell(by the inhibition of adsorption, penetration or uncoating).
(1)virolysis --- with the aid of complement----- by complement activation by
antibody-coated virus particles.
--- by phagocytosis -----opsonins in enhancing phagocytosis of virus particles
--- by ADCC
(2)Neutrilizing virion: act on free viruses , but can’t influence intracellular virus
directly.
2). Non-neutrilizing antibody:
hemagglutination inhibition antibodies
complement fixation antibodies:
2.
Cell mediated immunity:
the destruction of an infected cell before progeny particles are released --- an effective
way of terminating a viral infection.
CTL: react with membrane-bound viral antigens and lyse the infected cells.
release some lymphokines(IFN-r, TNF ).
Th : release lymphokines.
NK cell: lyse infected cell directly.
Section III
Immunity against fungi
I . Non-specific immunity:
A. Inherent Barriers
Skin, Mucus, Ciliated epithelium, Low pH
B. Phagocytic cells
C. Humoral and cellular components. --- IFN, TNF-a
II. Specific immunity
1. Humoral immunity----antibody
2. Cell mediated immunity:
Th : release lymphokines.
Chapter 5
Section I
Bacterial
Genetics and Variation
inheritance
and
variation.
Concept:
(1) heredity(inberitance)
general
stability
on
“likeness”
characteristics of progeny and parent.
(2) variation . the difference between progeny and parent
variation
genetic
substance
changes .nonberitable
enviroment changes
I.
variation examples.
1. shape and structure variation .
2. colony variation
smooth colony
rough
colony
3. virulence variation, vaccine
BCG : Bacilla of calmetter-Gueria 230 passages, 13
years.
4. Resistance variation
II. Genetic substance
1. chromosome
consists of a circular double strand DNA molecular, control
life without introne.
2. Plasmid
Extrochromosomal genetic substance. Circle double strand DNA
（1）
autonomous replication
binding to chromosome —episome
（2）contral most of auxiliary functions of bacterial cell
Antibiotic resistance —R plasmid .
production of fimbriae—F plasmid
bacteriocin —E. coli con plasmid.
in
the
Heritable
variation
bacterial
（3）dispensable, it can be lost .
（4）tranfer from a bacteria to another
conjugative plasmid : F+
serpili
nonconjugative
plasmid: phage
（5）Incompatibility and compatibility.
Incompatibility:
compatibility : bacterium can carry one or several
small—a few genes .large—hundreds of genes.
3. bacteriophage.
plasmid, different
size :
Bacteriophage
Infecting bacterial virus .
(1) viral common properties
smallest ,simple structure , DNA/RNA, parasite in living cell
(2) widespread existence
(3) high host –specific parasitism
I. Biological properties
1. Shape and structure
Seen by EM: Tadpol , microsphere slim rod
Structure: head core: DNA/RNA
Capsid: protein coat
Tail: pipe-like, collar, base plate, tail fib
II. Interrelation between phage and bacteria
1. Virulent phage.
Reproduction and lyzing Bacteria, which can replicate in cell
and released in lysis of B .
Replication cycle.
1) absorption and tail pins and fibers absorb teichoic receptor of B,
2) penetration : lysosome like substance lyse, injects DNA into bacteria.
3) Biosynthesis structure
Phage DNA
transcribe mRNA
protein, enzyme
phage DNA replication
4) lysis
encode lysosome
lysis B.
release
2. lysogenic phage. infected bacterial phage doesn’t replicate it’s gene ,integrated
with bacterial DNA, its replication is associated with bacterial DNA
lysogenic phage (temperate phage)
lysogenec bacteria
prophage : The DNA of temperate phage integrated into bacterial DNA.
4.transposon: a segment of DNA that can become integrated at many different sites
along a chromosome,plasmid and phage.(especially a segment of bacterial DNA that
can be translocated as a whole)
transposable elements
insertion sequence
transposon
III.
Mechanism of bacterial variation:
1. Mutation
（1）
concept: a stable heritable change of bacterial gene ,
spontaneous 10－6～10－9
inducing
mutagen
（2） type of mutation
molecular foundation of mutation .
Bacterial nucleotide sequence change
i.
base replacements
transition (转换) A—G, C—T
transversion（颠换）A—T C—G
ii.
base deletion . one base or fragment lost
iii.
base insertion . one base or fragment
2. genetic transfer and recombination
1) Genetic substance of B. is transferred to another bacteria.
Donor bacteria : provide genetic substand
Recipient bacteria : accept genetic substand
2) transformation
recipient B. takes up exogenous DNA of donor B.
eg : Griffith’s experiment
competence : bacterial state. In which bacteria can able to take up DNA from
environment in logarithmic phase
3) transduction .
donor bacterial DNA is transfered to recipient bacterial by phage .
（1） general transduction: any fragment of donor bacteria is transfered.
（2） Specific transduction: the fragment near attachment is transfered.
（3） Lysogenic conversion
Bacteria acquired new properties by phage lysogenization.
Eg C, diphtheria
4) conjuqation
bacterial DNA is transferred from donor bacteria to recipient bacteria
by F pilus. Hfr(high frequent recombinant bacterium )
（1）F plasmid F’ plasmid intergrated into chromosome.
F plasmid of high freguent recombinant bacteria separated from
bacteria chromosome, carrying a neighbour DNA.
Sexduction.
（2）R plasmid
conjugative R plasmid resistance transfer factor RTF
resistance factor (RF)
the function of RTF is similar to F plasmid
nonconjugative R plasmid.
The result of gene tranfer :
i. exogenous DNA was degraded
ii exogenous DNA from circular ds DNA
autonomous replication
abortive infection
iii. exogenous DNA recombine with endogenous DNA
hemologeous recombination
site-spcific recombination
eg
phage
4) lysogenic conversion
5) protoplast fusion
III.
Medical application
1, Bacterial indentification
2. prevention treatment of diseases. Eg . vaccine
3. screening potential carcinogen . Ames test
4. genetic engineering
（1）prepare objective gene endonuclease
E COR
（2）objective gene recombines with vector
vector: plasmid .phage .
（3）recombined DNA transfer to cell .eg . E. coli
（4）Screen positive cell.resistance—antibiotics.
(5) Amplify objective gene and express.
Section II
I
Viral Genetics
The nature of the viral genome (RNA or DNA; segmented or nonsegmented) plays an
important role in the genetics of the virus.
1. Mutations:
----permanent changes in sequence of nucleotides in nucleic acid.
----TYPES OF MUTATION:
Mutants can be point mutants (one base replaced by another) or insertion/deletion
mutants.
---- ORIGIN
(1)Spontaneous mutations
These arise naturally during viral replication: e.g. due to errors by the
genome-replicating polymerase or a result of the incorporation of tautomeric（异构）
forms of the bases.
(2) Mutations that are induced by physical or chemical means
Chemical:
Agents acting directly on bases, e.g. nitrous acid
Agents acting indirectly, e.g. base analogs which mispair more frequently than
normal bases thus generating mutations
Physical:
Agents such as UV light or X-rays
---- EXAMPLES of Mutant(突变株)
e.g. temperature sensitive (ts) mutants, ts 突 变 株 - These will grow at low
temperature e.g. 31 degrees C but not at e.g. 39 degrees C, wt grows at 31 and 39
degrees C. It appears that the reason for this is often that the altered protein cannot
maintain a functional conformation at the elevated temperature.
2. Recombination (重组)and reassortment（重配）:
--- Recombination (重组) :exchange of genetic material between two viruses which
infected the same cell. This involves breaking of covalent bonds within the nucleic
acid, exchange of genetic information, and reforming of covalent bonds.
----reassortment（重配）: If a virus has a segmented genome and if two variants of
that virus infect a single cell, progeny virions can result with some segments from one
parent, some from the other.
3. Integration(整合)： viral genome insert into host cell genome .
4. Complementation(互补作用)：
If we infect the same cell with both mutants, each mutant can provide the missing
function of the other and therefore they can replicate.
5. Phenotypic mixing: If two different viruses infect a cell, progeny viruses may
contain coat components derived from both parents and so they will have coat
properties of both parents. This is called phenotypic mixing. INVOLVES NO
ALTERATION IN GENETIC MATERIAL.
Chapter 6
Medical Ecology and hospital infection
Section I
normal
flora
I. Concept:
1. normal flora: The microbes that parasitize on the body surface or tracts connecting
with external, while don’t harm the host in ordinary condition.
2. Distribution of normal flora
Mouth carity anaerobes
Intestinal tract: anaerobes: aerobes =1000:1
Vagina: Lactobacillus.
Skin
Respiratory
3. Roles of normal flora.
(1) Biological barrier: antagonism
(2) nutrient synthesize : aa. VB. K. enhance absorb.
(3) immue: enhance and develop and maturation of immue system
acts as an antidysbacteriosis drug and as an immunostimulator. It stimulates T-cell
immunity, phagocytosis, B-cell immunity. Immunostimulating effect of bioflor
depends on dysbacteriosis degree and is maximal at its first stages.
(4) Anti- caducity
(5) Anti-tumor
Secton II
Flore disequilibrium (dysbacteriosis)
I. Flore disequilibrium (dysbacteriosis): Balance of normal flora was broken. Flora
inbalance symptom (superinfection) widely use antibiotics, sensitive bacteria were
killed , the resistant bacteria reproduce rapidly.
II. main reasons:
1. antibiotic therapy
2. change their normal parasite sites.
they leave their ordinary habitant and gain
access to other part.
3. host immunity reduce.
Owing to the wide use of antibiotic, hormone and anti-concer druges.
Section III
opportunistic infection
I . opportunistic pathogenic B
some bacteria are unable to cause in ordinary condition , but can initiate infection
under some certain condition.
II. Characters of opportunistic pathogenic B
1. weak or no-more apparent virulence
2. drug-resistant bacteria or multiresistant bacteria
3. new opportunistic pathogenic B
Section IV Hospital infection
I. Concept:
Hospital infection / nosocomial infection: Infections acquired during hospital stays.
Incidence (annual): estimated 2 million cases annually or about 10% of American
hospital patients (CDC/NNIS 1992)
Incidence Rate: approx 1 in 136 or 0.74% or 2 million people in USA
II. Types:


Nosocomial infections by site:
o Urinary tract infections
o Surgical site infections
o Respiratory tract infections
o Blood stream infections
o Skin infections
o Gastrointestinal tract infections
o Central nervous system infections
Nosocomial fungal infections - fungi cause about 9% of nosocomial
infections.
o Candida
o Candida albicans
o Aspergillus
o
Fusarium
Trichosporon
o Malassezia
Nosocomial pneumonia
o Bacterial pneumonia
o Legionnaires' disease
o Pulmonary aspergillosis
o Mycobacterium tuberculosis
o Viral pneumonias
o Respiratory Syncytial Virus
o Influenza
Nosocomial infections by pathogen:
o Staphylococci
o Pseudomonas
o Escherichia coli
Antibiotic-resistant nosocomial infections
o Methicillin resistant staphylococcus aureus (MRSA)
o Vancomycin-resistant staphylococcus aureus
o Vancomycin-resistant enterococci (VRE)
o



III. Who gets Nosocomial infections?
Patient Profile: Typically immunosuppressed hospital patients due to age, disease,
medication, or surgery.
IV. Prevention of Nosocomial infections
1.Changes to hospital staff activities:
2. Changes to the patient environment:
3. Changes to hospital environment:
4. Vaccination - use of certain vaccines may be appropriate for some patients.
Chapter 7
Disinfection and sterilization
Concepts:
1. disinfection : To kill pathogenic microorganisms (vegetative form)
2. sterilization : To kill all microorganisms, including .pathogenic & non-pathogenic ,
vegetative &spore.
3. asepsis : a state of sterility (no living bacteria) ,
asepsis / antiseptic technique: the technique to prevent bacteria entering human
body and other matters.
Aseptic technique is used in a variety of research applications, including:
Animal husbandry ( immuno-compromised / barrier animals)
Tissue and cell culture
Diagnostics and animal healthcare procedures
Survival surgical procedures
4. antisepsis: To inhibit the growth and reproduction of bacteria in vitro.
5. bacteriostasis: prevention of growth of bacteria, but without killing them.
Bacteriostat: agent causing bacteriostasis.
Section I.
Physical methods
I. heat lethal
make bacterial protein denature. bacterial DNA degrade, injury cell membrane .
1. dry heat:
(1) flame
(2) burn
(3) hot air oven: 160---170°C, 2―3hrs
(4) infrared
vegatatine 80---100°C
1hr
spore
160°C
2hrs
2. moist heat :
1)advantages over dry heat:
(1)
Bacteria absorb H2O , proteinis easy to solidify and denature .
(2)
Strong penetration
Eg. 100 th layer: dry heat 130-140°C 4hrs。72.5°C/100 th
Moist heat 105°C 3hrs. 101°C/100 th
(3) lalent heat gas –liquid .
2) Methods:
(1) pasteurization 62°C 30′ 72°C ， 30″
(2) Boiling 100°C
5′
(3) Steaming and intermittent sterilization:
Arnold 3times.
2
(4) Autoclaving ： 1.05 kg/ cm ， 121.3°C 15－30′－spore
II.radiation
1. ultraviolet light: 200---300nm
interfere DNA replication ,form dimmer of Thymine .
strongest spectrum 260nm, DNA absort specfurm,
weak penetration : definite time and intensity
stimulate skin, eyes,.
Application : air . operation room
2. ionizing radiation : eg ,x-ray, r-ray.
III. filtration
fiter
heat－labile solution
eg. Serum . toxin .antibiotics. etc.
seitz filter: K>EK>EK-S
glassical filter: G1 G2
G3……6
thin membrane filter
IV. Other: low temperature ( preserve bacteria)
Section II
Chemical
disinfection
Disinfectant:
Antiseptic:
1. chemical agents and mechanism
1) heavy –metal salts
(1) bind to –SH and destroy it, inhibit activity of enzymes.
(2) Protein denature. Merbromin .thimerosal 0.1%disinfectant
0.01%antiseptic
2) Oxidizer
H2 O 2 KMnO 4 CHCOOH(过氧乙酸)
Halogen（iodine ，chlorinated lime）
(1) SH
S—S—
enzyme
(2) destroy amino group, indol group.
(3) denature protein
3) surfactant
combine with phospholipid
increast membrane permeability
bromogeramine(新洁尔灭)
domiphen（杜灭芬）
4） aldehyde（醛类）
farmaldehyde、
enzyme deactivity
5） alcohol 70％ alcohal protein denature。
6）phenol （酚类）protein denature ， destroy cell membrane。
2． Application
skin： 2.5％碘酒 70％酒精
mucosa 2％ 红汞
0.1％新洁尔灭
drinking water 漂白粉
patients excreta 5％ phenol 2％lyson
air: formalin spray
3． Affecting factors
(1) concentration and
time
(2) properties and quantity
(3) temperature
and
PH
(4) antagonist: organs protein, excreta
Chapter 8 The Examination and Treatment of Microbes
Infection
Section 1.
The Examination of Bacterial Infection
I. Detection of pathogenesis bacteria.
1. Getting a pure culture : aseptic technique + sterile media:
2. Microscopy and stains: electron microscopy.
3. isolation and identification.
a. micromanipulation
b. extinction dilution in liquid media
c. solid media - streaking out, viable counts
d. enrichment culture
e. Composition of culture media, temperature of incubation, osmotic potential of
media, pH etc.
f. Anaerobe or aerobe? - microaerophile?
II. Detection of pathogenesis bacteria antigens
III. Others:
1. antibody
2. nucleic acid
Section 2.
The Examination of Viral Infection
I. Detection of living virus:
1. animal injection(动物接种):
2. chicken embryo culture（鸡胚培养）：
3. cell culture（细胞培养）:
primary（原代）cell culture:
continuous (传代) cell culture:
growth phenomenon of virus:
(1) cytopathic effect (CPE)（细胞病变）:
--The presence of the virus often gives rise to morphological changes in the host
cell. Any detectable changes in the host cell due to infection are known as a
cytopathic effect.
--Cytopathic effects (CPE) may consist of cell rounding, disorientation, swelling
or shrinking, death, detachment from the surface, etc.
(2) plaque forming units (PFU)（空斑形成单位）:
A plaque is produced when a virus particle infects a cell, replicates, and then kills that
cell. Each plaque is the result of infection of one cell by one virus followed by
replication and spreading of that virus. So we use PFU/ml to show virus’ quantity.
(3) inclusion body----- round, oval, or irregular-shaped bodies occurring in the
cytoplasm and nuclei of virus-infected cells, as in disease caused by filtrable virus
infection such as rabies, smallpox, herpes, etc; called also elementary b's and
intranuclear inclusions.
II. Detection of viral antigen and antibody:
ELISA, immuno-fluorescence , Western-blot
III. Detection of viral nucleic acid:
PCR,
RT-PCR,
Biochip （生物芯片）
Section III The Examination of fungi Infection
I. Samples:
Skin scrapings suspected to contain dermatophytes or pus from a lesion can be
mounted in KOH on a slide and examined directly under the microscope.
II. detection and identification:
1. Direct microscopy.
2. Culture and identification
(1) Sabouraud dextrose agar:
(2) Culture methods:
3. Skin testing (dermal hypersensitivity)
III. quick diagnosis:
1. Serology:
latex agglutination may favor the detection of IgM antibodies,
double immunodiffusion and complement fixation usually detect IgG antibodies.
Some EIA tests are being developed to detect both IgG and IgM antibodies.
2. detection of nucleic acid:
3. Biopsy and histopathology.
Gomori methenamine silver (GMS) stain.
Section IV Prevention and Treatment of microbes infection
I. Immunization Prevention of infection：
1. Vaccines:
(1) inactivated vaccines:
(2) attenuated-live vaccines:
(3) *gene engineering vaccines: Fragments of the genome of the virus that the
vaccine is intended to combat are inserted into protein expression vector and then
transfected into bacteria, yeast or eukaryotic cell. these micro-organisms then
produce enormous quantities of a protein (a recombinant protein) which will be
purified and used as the basis for the vaccine.
(4) *DNA vaccines:
(5) *recombined viral vector vaccines：
(6) synthesized(合成) vaccines:
(7) subunit vaccines
2. toxoid
3. Artificial passive immunization:
(1) antitoxin
(2) antisera
(3) PLACETAL GAMMAGLOBULIN
(4) OTHERS
II. Treatment of bacterial infection:
1. INHIBITORS OF CELL WALL SYNTHESIS
PENICILLIN---2. Inhibitors of the functions of cell membrane
3. Inhibitors of Protein Synthesis (most bacteriostatic)
(1) Antimicrobials that Bind to the 30S Ribosomal Subunit
aminoglycosides irreversibly bind to the 30S ribosome and freeze the 30S initiation
complex (30S-mRNA-tRNA)
tetracyclines reversibly bind to the 30S ribosome and inhibit binding of
aminoacyl-t-RNA to the acceptor site on the 70S ribosome.
(2) Antimicrobials that Bind to the 50S Ribosomal Subunit
Chloramphenicol, lincomycin, clindamycin (bacteriostatic)---These antimicrobials
bind to the 50S ribosome and inhibit peptidyl transferase activity
Erythromycin ---- The macrolides inhibit translocation.
4. Inhibitors of Nucleic Acid Synthesis and Function
(1). Inhibitors of RNA Synthesis and Function
Rifampin, rifamycin, rifampicin (bactericidal)----These antimicrobials bind to
DNA-dependent RNA polymerase and inhibit initiation of RNA synthesis.
(2). Inhibitors of DNA Synthesis and Function (bactericidal)
Quinolones - nalidixic acid, ciprofloxacin, oxolinic acid----- These antimicrobials
bind to the A subunit of DNA gyrase (topoisomerase) and prevent supercoiling of
DNA, thereby inhibiting DNA synthesis.
III. Treatment of viral infection:
1. antiviral agents---chemical agents:
（1）Nucleoside analogues polymerase inhibitors.
ACV(acyclovir),无环鸟苷――treatment of HSV through the inhibition of the
viral DNA polimerase.
Ara-A (Adenine arabinoside),阿糖腺苷——treatment of HSV，VZV，CMV
through the inhibition of the viral DNA polimerase.
AZT(Azidothymidine ) , 叠 氮 胸 苷 — — inhibit reverse transcriptase in the
retroviruses， used in HIV infection
Lamivudine,拉米呋定—— inhibit reverse transcriptase in the retroviruses， used
in HIV and HBV infection
Ribavarin,病毒唑 —— inhibit RNA and DNA polymerase, used in influenza
virus infections
（2）Non-Nucleoside analogues polymerase inhibitors.
（3）Protease inhibitors
Saquinavir. inhibitors of HIV replication.
Ritonavir, Indivavir. They are the most potent inhibitors of HIV replication to date.
2. gene therapy:
antisense oligonuclotide,asON 反义核酸
ribozyme 核酶
siRNA
3. immunal therapy:
Ab
Ck
IFN
Section IV TREATMENT of Fungi
The primary antifungal agents are:
1. Amphotericin B.
It has a greater affinity for ergosterol（麦角固醇） in the cell membranes of fungi than
for the cholesterol in the host's cells; once bound to ergosterol, it causes disruption of
the cell membrane and death of the fungal cell.
2. Azoles（多稀类，唑类）
The general mechanism of action of the azoles is the inhibition of ergosterol
synthesis.
3. Griseofulvin（灰黄霉素）
Its effect depends on its accumulation in the stratum corneum where it is incorporated
into the tissue and forms a barrier which stops further fungal penetration and growth.
4. 5-fluorocytosine
5-fluorocytosine (Flucytosine or 5-FC) inhibits RNA synthesis and has found its
main application in cryptococcosis.
Chapter 9
Antimicrobial Drug Resistance
I. Principles and Definitions
Drug resistance is the ability of the parasite species to survive and/or multiply despite
the administration and absorption of a drug given in doses equal to or higher than
those usually recommended but within the limit of tolerance.
Clinical drug resistance to an antimicrobial agent occurs when the MIC of the drug for
a particular strain of bacteria exceeds that which is capable of being achieved with
safety in vivo.
II. Resistance to an antimicrobial can arise :
(1) by chromosomal mutation in the gene that determines sensitivity/resistance to the
agent
(2) by acquisition of extrachromosomal DNA (plasmid) carrying a resistance gene.
(3) by acquisition of transposable element carrying a resistance gene.
Resistance that appears after introduction of an antimicrobial agent into the
environment usually results from a selective process, i.e. the agent selects for survival
of those strains possessing a resistance gene.
Resistance can develop in a single step or it can result from the accumulation of
multiple mutations.
III. Mechanisms of Resistance
1. Altered permeability of the antimicrobial agent - Altered permeability may be due
to the inability of the antimicrobial agent to enter the bacterial cell or alternatively to
the active export of the agent from the cell.
2. Inactivation of the antimicrobial agent - Resistance is often the result of the
production of an enzyme that is capable of inactivating the antimicrobial agent.
3. Altered target site - Resistance can arise due to alteration of the target site for the
antimicrobial agent.
4. Replacement of a sensitive pathway - Resistance can result from the acquisition of
a new enzyme to replace the sensitive one.
IV. Control of Resistance
1. correct usage of antibiotics
(1) Optimising drug dosages and delivery routes
Two major factors contribute to the emergence and spread of antimicrobial
resistance in hospitals: a high rate of antimicrobial drug use and inadequate
infection control practices.
The routine reporting of susceptibility results;monitoring antimicrobial use with
feedback to physicians concerning inappropriate use;
(2) Selection of drugs - Use conventional drugs first in uncomplicated cases.
Greater the exposure, higher will be the emergence of resistance.
(3) Monitoring for resistance and early treatment of these cases to prevent their
spread.
2. Clear policy of using antibiotics.
Some use of antibiotics (preventive, therapeutic, growthpromoting) in food
animals contributes to the pool of resistant human pathogens. Both medical and
nonmedical uses of antibiotics should be reduced.
3. Studies of new antibiotics
4. get rid of the plasmid.
5. Evaluation of drug rotation strategies