1. oral cavity (mouth), pharynx (throat), esophagus
- physical factors - mucus (microbes stick to it), sloughing epithelium (cells constantly get rubbed off), saliva (washes microbes down the throat), peristalsis (squeeze microbes down)
- chemical factors - saliva (enzymes can break down microbes), mucus (toxic to microbes)
- cellular factors - phagocytes (white blood cells that gobble up microbes), normal microbiota (bacteria that normally live in you and compete with entering microbes for food and space)
2. stomach
- physical factors - mucus (microbes stick to it), sloughing epithelium (cells constantly get rubbed off), peristalsis (squeeze microbes down)
- chemical factors - HCl (pH ~2), pepsin (digestive enzyme)
- cellular factors - none (?)
3. small intestine
- physical factors - mucus (microbes stick to it), sloughing epithelium (cells constantly get rubbed off), peristalsis (squeeze microbes down)
- chemical factors - digestive enzymes from pancreas, and bile from gall bladder
- cellular factors - none (?)
4. large intestine - includes colon, rectum and anus
- physical factors - mucus (microbes stick to it), sloughing epithelium (cells constantly get rubbed off), peristalsis (squeeze microbes down)
- chemical factors - anaerobic conditions (many microbes can't live wothout oxygen)
- cellular factors - phagocytes; normal microbiota (100 billion bacteria per gram of fecal material in large intestine)
Epidemiology: Transmission
- fecal/oral - feces gets contaminated and often gets transmitted to hands via improper handwashing habits, and can then get to the mouth; generally lots of microbes are required to pass infection this way.
- reservoirs - animal that is hosting the microbe; can be in humans (in feces, lesions, etc.), in animals (in feces, urine, etc.), and in soil.
- vehicles - nonliving things that can provide a habitat for the microbes until they infect thier host; usually food and water.
- predisposing factors - some people are more prone to getting an infection, such as those who have had a gastrectomy (stomach-reducing surgery), achlorlydria (lack of enough hydrochloric acid in the stomach), antacid therapy; intestinal obstructions, antimicrobial agent therapy (antibiotics), malnutrition, and immaturity (infants).
About 76 million people are sickened annually by food-borne bacteria, with 325,000 hospitalized and 500 deaths in the United States alone!