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

Introduction w What is normal flora? w “In the absence of these organisms, life as we know it would be impossible.” (page 83) w Human fetus is sterile After birth, many microbes take up residence w Exposure to a microbe leads to one of the following outcomes: Transient colonization Permanent colonization Disease

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

Normal Flora and Pathogens w 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 w How do we decide what is causing the disease? You must exclude other known pathogens! w External Ear: Normal Flora – Coagulase negative Staph Pathogens – Pseudomonas aeruginosa, etc.

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

Normal Flora and Pathogens w Esophagus: Normal Flora – usually no permanent flora Pathogens – rare for bacteria w Stomach: Normal Flora – few acid tolerant species (Lactobacillus and Streptococcus) Pathogens – Helicobacter pylori

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

Normal Flora and Pathogens w 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 w 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 w Skin: Normal Flora Almost all Gram + Coagulase (-) Staph Corynebacteria Propionibacteria Clostridium perfringens (20% of healthy individuals) Pathogens – Coagulase (+) Staph, Streptococcus pyogenes