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Tufts OpenCourseware
Author: Amelia Virostko

1. Introduction

  1. Anaerobic bacteria in mouth and upper respiratory tract, GI tract, and female genital tract
  2. Different bacterial concentrations and species at different anatomic levels
    1. Factors that control bacterial concentration
      1. Gastric acidity
      2. Bile
      3. Propulsive motility
      4. Short-chain fatty acids made in the large bowel
      5. Natural antibiotics f. redox potential
  3. Normal flora varies with age, loss of teeth, menstrual cycle, and pregnancy

2. Functions of Normal Intestinal Flora

  1. Metabolizing dietary nutrients not digested by host intestinal enzymes
  2. Producing vitamins in the GI tract (vitamin K and folate)
  3. Metabolizing endogenous substances in GI tract
  4. Metabolizing certain pharmaceuticals (e.g. digitalis, cyclamate)

3. Effect of Antibiotics

  1. Also suppress normal flora
    1. Beneficial effects
      1. Suppress flora before elective intestinal operations to prevent infections
      2. Suppress bacteria that catabolize urea to ammonium in patients with cirrhosis
      3. Ppromotes growth in animals fed minimal diet
    2. Harmful effects
      1. Emergence of antibiotic-resistant bacteria
      2. Growth of pathogens caused by suppressing normal flora

4. Role of Microorganisms from the Normal Flora in Disease

  1. UTIs mostly caused by E. coli from GI tract
  2. Peritonitis and intra-abdominal abscesses from colonic flora
  3. Gallbladder infections from intestinal microbes
  4. Septicemia from intestinal bacteria, especially in persons with liver cirrhosis