BIO 411 – Medical Microbiology

1. BIO 411 – Medical Microbiology Chapter 9 Commensal and Pathogenic Microbial Flora

2. 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

3. 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

4. Introduction • Strict pathogens always cause disease • Mycobacterium tuberculosis • Neisseria gonorrhoeae • Rabies virus • Opportunistic Pathogens – many normal flora organisms

5. 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

6. 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.

7. Normal Flora and Pathogens • Lower Respiratory Tract: • Normal Flora – usually none • Pathogens: • S. pneumoniae • S. aureus • Klebsiella pneumoniae • Peptostreptococcus spp.

8. 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

9. Normal Flora and Pathogens • Small Intestine: • Normal Flora: • Mostly anaerobes (Peptostreptococcus spp., etc.) • Pathogens: • Salmonella and Campylobacter spp.

10. 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)

11. 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

12. Normal Flora and Pathogens • Vagina: • Normal flora – lactobacillus, streptococcus, staphylococcus, others • Pathogens: • Candida albicans and C. glabrata • Neisseria gonorrhoeae and Chlamydia trachomatis

13. 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