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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

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bio 411 medical microbiology

BIO 411 – Medical Microbiology

Chapter 9

Commensal and Pathogenic Microbial Flora

introduction
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
introduction1
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
introduction2
Introduction
  • Strict pathogens always cause disease
    • Mycobacterium tuberculosis
    • Neisseria gonorrhoeae
    • Rabies virus
  • Opportunistic Pathogens – many normal flora organisms
normal flora and pathogens
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 pathogens1
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 pathogens2
Normal Flora and Pathogens
  • Lower Respiratory Tract:
    • Normal Flora – usually none
    • Pathogens:
      • S. pneumoniae
      • S. aureus
      • Klebsiella pneumoniae
      • Peptostreptococcus spp.
normal flora and pathogens3
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 pathogens4
Normal Flora and Pathogens
  • Small Intestine:
    • Normal Flora:
      • Mostly anaerobes (Peptostreptococcus spp., etc.)
    • Pathogens:
      • Salmonella and Campylobacter spp.
normal flora and pathogens5
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 pathogens6
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 pathogens7
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 pathogens8
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
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