Lecture 2 - Normal Flora
1. Introduction
- Anaerobic bacteria in mouth and upper respiratory tract, GI tract, and female genital tract
- Different bacterial concentrations and species at different anatomic levels
- Factors that control bacterial concentration
- Gastric acidity
- Bile
- Propulsive motility
- Short-chain fatty acids made in the large bowel
- Natural antibiotics f. redox potential
- Factors that control bacterial concentration
- Normal flora varies with age, loss of teeth, menstrual cycle, and pregnancy
2. Functions of Normal Intestinal Flora
- Metabolizing dietary nutrients not digested by host intestinal enzymes
- Producing vitamins in the GI tract (vitamin K and folate)
- Metabolizing endogenous substances in GI tract
- Metabolizing certain pharmaceuticals (e.g. digitalis, cyclamate)
3. Effect of Antibiotics
- Also suppress normal flora
- Beneficial effects
- Suppress flora before elective intestinal operations to prevent infections
- Suppress bacteria that catabolize urea to ammonium in patients with cirrhosis
- Ppromotes growth in animals fed minimal diet
- Harmful effects
- Emergence of antibiotic-resistant bacteria
- Growth of pathogens caused by suppressing normal flora
- Beneficial effects