《微生物学》课程PPT课件讲稿（英文版）Lecture 2 Microbial Pathogenesis and Host-Parasite Relationships

Normal flora General aspects Remember definition organisms frequently found on or within body of healthy individuals Most are bacteria but some are viruses fungi, and protozoa We do not carry all of them all of the time Each person has individualized normal flora BIOL 533 Lecture two

BIOL 533 2 Lecture Two Normal Flora • General aspects – Remember definition: organisms frequently found on or within body of healthy individuals – Most are bacteria, but some are viruses, fungi, and protozoa • We do not carry all of them all of the time • Each person has individualized normal flora

Normal flora Some are found only on body others also found in environment Problem: some people have transient normal flora(pathogens) Example: about 10% of population have meningococcus or pneumococcus as normal flora BIOL 533 Lecture two

BIOL 533 3 Lecture Two Normal Flora • Some are found only on body; others also found in environment • Problem: some people have transient normal flora (pathogens) – Example: about 10% of population have meningococcus or pneumococcus as normal flora

Importance Opportunistic infections: normal flora in unusual sites; for example Bacteriodes from intestine into deeper tissues as a result of trauma(or surgery Staphylococci from skin and nose Streptococci and gram cocci from throat and mouth BIOL 533 Lecture two

BIOL 533 4 Lecture Two Importance • Opportunistic infections: normal flora in unusual sites; for example: – Bacteriodes from intestine into deeper tissues as a result of trauma (or surgery) – Staphylococci from skin and nose – Streptococci and Gram— cocci from throat and mouth

Importance Depends on pathogen and on defenses of host i Candida(yeast causes pneumonia in people undergoing cancer chemotherapy Pneumocystis carinii(common inhabitant of lung causes pneumonia and death in AIDS patients BIOL 533 Lecture two

BIOL 533 5 Lecture Two Importance • Depends on pathogen and on defenses of host: – Candida (yeast) causes pneumonia in people undergoing cancer chemotherapy – Pneumocystis carinii (common inhabitant of lung) causes pneumonia and death in AIDS patients

Immune stimulation Antigenic stimulation by normal flora do not have high antibody titers Serve as defense mechanism even in low concentration Bacterial stimulation leads to production of Iga that is secreted through mucus membranes Probably interfere with colonization of deeper tissues BIOL 533 Lecture two

BIOL 533 6 Lecture Two Immune Stimulation • Antigenic stimulation by normal flora— do not have high antibody titers – Serve as defense mechanism even in low concentration – Bacterial stimulation leads to production of IgA that is secreted through mucus membranes • Probably interfere with colonization of deeper tissues

Immune stimulation Sometimes antibodies elicited by normal flora cross-react with normal tissue Antibodies against ABo blood group substances .A- make b antibodies ·B- make a antibodies .0-make antibodies against both Why? Bacteria from intestinal flora contain Ag that cross-react with both a &b blood substances BIOL 533 7 Lecture two

BIOL 533 7 Lecture Two Immune Stimulation • Sometimes antibodies elicited by normal flora cross-react with normal tissue: – Antibodies against ABO blood group substances: • A - make B antibodies • B - make A antibodies • O - make antibodies against both – Why? Bacteria from intestinal flora contain Ag that cross-react with both A & B blood substances

Immune stimulation Cross-reactivity does not normally cause disease Possible for antibodies cross-reactive to microbial Ag to cause problem Lupus erythematosus-production of Ab against host dna Some evidence that ag may be cross-reacting bacterial LPS May cross-react with pathogen(meningococcus) BIOL 533 Lecture two

BIOL 533 8 Lecture Two Immune Stimulation • Cross-reactivity does not normally cause disease – Possible for antibodies cross-reactive to microbial Ag to cause problem • Lupus erythematosus—production of Ab against host DNA – Some evidence that Ag may be cross-reacting bacterial LPS • May cross-react with pathogen (meningococcus)

Phyl& hemical Aspects带 Keeps out invaders Mechanisms Physical advantage of previous occupancy Some produce bacteriocins or antibiotics Relevance to lab work e coli K-12 cannot compete with intestinal flora BIOL 533 Lecture two

BIOL 533 9 Lecture Two Physical & Chemical Aspects • Keeps out invaders – Mechanisms: • Physical advantage of previous occupancy • Some produce bacteriocins or antibiotics – Relevance to lab work: E. coli K-12 cannot compete with intestinal flora

Phyl& hemical Aspects带 Antibiotic effects: wipes out normal flora Both endogenous and exogenous organisms can cause disease Infecting dose of Salmonella decreases one million-fold when mice given streptomycin Patients treated with some potent antibiotics Suffer from diarrhea due to overgrowth of yeasts and staphylococci Administration of clindmycin -Clostridium difficile(minor member of normal flora) causes pseudomembranous colitis BIOL 533 Lecture two

BIOL 533 10 Lecture Two Physical & Chemical Aspects • Antibiotic effects: wipes out normal flora – Both endogenous and exogenous organisms can cause disease • Infecting dose of Salmonella decreases one million-fold when mice given streptomycin • Patients treated with some potent antibiotics: – Suffer from diarrhea due to overgrowth of yeasts, and staphylococci – Administration of clindmycin-Clostridium difficile (minor member of normal flora) causes pseudomembranous colitis

Phyl& hemical Aspects带 Role in human nutrition and metabolism E, coli and bacteriodes synthesize vitamin K Metabolism of key compounds involves excretion from liver into intestine and their return to the liver BIOL 533 Lecture two

BIOL 533 11 Lecture Two Physical & Chemical Aspects • Role in human nutrition and metabolism – E. coli and Bacteriodes synthesize vitamin K – Metabolism of key compounds involves excretion from liver into intestine and their return to the liver