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BIO 411 – Medical Microbiology. Chapter 9 Commensal and Pathogenic Microbial Flora. Introduction. What is normal flora? “In the absence of these organisms, life as we know it would be impossible.” (page 83) Human fetus is sterile After birth, many microbes take up residence - PowerPoint PPT Presentation
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BIO 411 – Medical MicrobiologyChapter 9
Commensal and Pathogenic Microbial Flora
Introduction What is normal flora? “In the absence of these organisms, life as we
know it would be impossible.” (page 83) Human fetus is sterile
• After birth, many microbes take up residence
Exposure to a microbe leads to one of the following outcomes:• Transient colonization• Permanent colonization• Disease
Introduction Colonization vs. Disease
• Organisms that colonize a human do not interfere with normal body functions
• Those that cause disease lead to tissue damage
• Proliferation of the microbe
• Production of toxins/enzymes
• Host immune response
Introduction Strict pathogens always cause disease
• Mycobacterium tuberculosis• Neisseria gonorrhoeae• Rabies virus
Opportunistic Pathogens – many normal flora organisms
Normal Flora and Pathogens Mouth, oropharynx, nasopharynx:
• Normal Flora:• Many anaerobes (Peptostreptococcus spp.)• Aerobes: Streptococcus (viridans),
Haemophilus, Neisseria spp.
• Pathogens:• Streptococcus pyogenes (pharyngitis) • Sinusitis:• S. pneumoniae• Haemophilus influenzae• Neisseria meningitidis• Moraxella catarrhalis
Normal Flora and Pathogens How do we decide what is causing the
disease?• You must exclude other known
pathogens!
External Ear:• Normal Flora – Coagulase negative Staph• Pathogens – Pseudomonas aeruginosa,
etc.
Normal Flora and Pathogens Lower Respiratory Tract:
• Normal Flora – usually none• Pathogens:
• S. pneumoniae
• S. aureus
• Klebsiella pneumoniae
• Peptostreptococcus spp.
Normal Flora and Pathogens Esophagus:
• Normal Flora – usually no permanent flora
• Pathogens – rare for bacteria
Stomach:• Normal Flora – few acid tolerant species
(Lactobacillus and Streptococcus)• Pathogens – Helicobacter pylori
Normal Flora and Pathogens Small Intestine:
• Normal Flora:• Mostly anaerobes (Peptostreptococcus spp.,
etc.)
• Pathogens:• Salmonella and Campylobacter spp.
Normal Flora and Pathogens Large Intestine:
• Normal Flora (mostly anaerobes):• Bifidobacterium,
• Eubacterium,
• Bacteroides,
• Enterococcus, ect.
• Pathogens:• Bifidobacterium fragilis (most common anaerobe
causing intraabdominal disease)
• E. coli (most common aerobe causing intraabdominal disease)
• Enterococcus, Shigella spp.
• Clostridium difficile (antibiotic treatment)
Normal Flora and Pathogens Genitourinary System – normally
sterile with 2 exceptions:• Anterior urethra:
• Normal flora – lactobacillus, streptococcus, coagulase (-) staphylococcus
• Pathogens:– Enterococcus, E. coli, Candida spp.
– Neisseria gonorrhoeae and Chlamydia trachomatis
Normal Flora and Pathogens• Vagina:
• Normal flora – lactobacillus, streptococcus, staphylococcus, others
• Pathogens:– Candida albicans and C. glabrata
– Neisseria gonorrhoeae and Chlamydia trachomatis
Normal Flora and Pathogens Skin:
• Normal Flora• Almost all Gram +
• Coagulase (-) Staph
• Corynebacteria
• Propionibacteria
• Clostridium perfringens (20% of healthy individuals)
• Pathogens – Coagulase (+) Staph, Streptococcus pyogenes