Normal Flora

Normal Flora

1. what is it?

   • Bacteria and fungi that are permanent residents of certain body sites.
   • Commensals : organisms that derive benefit from another host but do not damage that host.

2. Roles

   • Causation of diseases
     • IN immunocompromised individuals
     • When nonpathogenic organism in their usual anatomical location can be pathogenic in other parts of the body
   • maintenance of health
     • colonization resistance
       • presence of the normal flora limit the growth of pathogen
         • E.g: antibiotic can reduce colonic flora
           • allowing Clostridium difficile growth , which is resistant to antibiotic
             • LEADING To: pseudomembrane colitis.
     • Serve a nutritional function
       • intestinal bacteria produce vitamin B and vitamin K

3. Main sites

   • Normal flora of genitourinary tract
     • Vigina
       • Lactobacillus species
         • keeps the pH of the adult woman's vagina low.
           • prevent the growth of potential pathogens
             • Upon taking antibiotic -->
               • overgrowth by C. albicans
                 • thus!
                   • Candida vaginitis
     • Urine in the bladder is sterile in the healthy person
   • Normal flora of GI tract
     • stomach
       • Due to its low pH it has a few organism
     • small intesine
       • most of it
         • small number of organism
           • bacteria
             • streptococci, and lactobacilli
           • yeast
             • C. albicans
       • terminal ileum
         • large number of organism
           • why?
     • colon
       • major location of bacteria in the body
         • More than 90% of the fecal bacteria is anaerobic
         • Most important aerobic bacteria: Escherichia coli
         • Most important anaerobic bacteria : Bacteroides fragilis
       • 20% of feces = bacteria
         • approx : 10^11 organisms/g.
       • major bacteria in colon ; table
       • Upon taking antibiotic therapy
         • normal flora will be surpassed
           • allowing a are organism
             • toxin-producing Clostridium difficile to overgrow
               • severe colitis
   • Normal flora of Skin
     • predominant (bacteria)
       • Staphylococcus epidermidis
         • Disease?
           • when reaches certain sites like artificial heart valves and prosthetic joint
     • yeast ( Candida albicans)
       • Can enter the body through needle pierce
       • in people with reduced cell mediated immunity --> systemic infection
     • 10^3−10^4 organism/ cm 2
   • Normal flora of respiratory tract
     • throat
       • Contain a mixture of : 1. viridans streptococci, 2. Neisseria species 3. S.epidermidis
         • attach to the pharyngeal mucosa
           • THUS!
             • Inhibit the growth of pathogens
               • 1. streptococcus pyrogens, 2. Neisseria meningitides 3. S.aureus
     • mouth
       • viridian's streptococci (half of the bacteria)
         • streptococcus mutans
           • found in large number in dental plaque
         • Can lead to bacterial endocarditis
       • Eikenella corrodens
         • cause skin and soft tissue infection with human bite
     • gingival crevices
       • Anaerobic bacteria
         • Bacteroides, Prevotella, Fusobacterium, Clostridium, and Peptostreptococcus,
           • Can cause abscess of the jaw, lungs, or abdomen

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