Summary

19.1  Anatomy and Normal Microbiota of the Digestive System

  • The digestive tract, consisting of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine, has a normal microbiota that is important for health.
  • The constant movement of materials through the gastrointestinal canal, the protective layer of mucus, the normal microbiota, and the harsh chemical environment in the stomach and small intestine help to prevent colonization by pathogens.
  • Infections or microbial toxins in the oral cavity can cause tooth decay, periodontal disease, and various types of ulcers.
  • Infections and intoxications of the gastrointestinal tract can cause general symptoms such as nausea, vomiting, diarrhea, and fever. Localized inflammation of the GI tract can result in gastritis, enteritis, gastroenteritis, hepatitis, or colitis, and damage to epithelial cells of the colon can lead to dysentery.
  • Foodborne illness refers to infections or intoxications that originate with pathogens or toxins ingested in contaminated food or water.

19.2  Microbial Diseases of the Mouth and Oral Cavity

  • Dental caries, tartar, and gingivitis are caused by overgrowth of oral bacteria, usually Streptococcus and Actinomyces species, as a result of insufficient dental hygiene.

19.3  Bacterial Infections of the Gastrointestinal Tract

  • Major causes of gastrointestinal illness include Staphylococcus spp., Helicobacter pylori, and Clostridium difficile bacteria.
  • C. difficile is an important cause of hospital acquired infection.
  • Different strains of E. coli, including ETEC, EPEC, EIEC, and EHEC, cause different illnesses with varying degrees of severity.
  • H. pylori is associated with peptic ulcers.
  • Rehydration and other supportive therapies are often used as general treatments.
  • Careful antibiotic use is required to reduce the risk of causing C. difficile infections and when treating antibiotic-resistant infections.

19.4 Viral Infections of the Gastrointestinal Tract

  • Common viral causes of gastroenteritis include rotaviruses and noroviruses.

19.5 Protozoan Infections of the Gastrointestinal Tract

  • Giardiasis are intestinal infections caused by protozoans.
  • Protozoan intestinal infections are commonly transmitted through contaminated food and water.
  • Treatment varies depending on the causative agent, so proper diagnosis is important.
  • Microscopic examination of stool or biopsy specimens is often used in diagnosis, in combination with other approaches.

19.6 Helminthic Infections of the Gastrointestinal Tract

  • Helminths often cause intestinal infections after transmission to humans through exposure to contaminated soil, water, or food. Signs and symptoms are often mild, but severe complications may develop in some cases.
  • Ascaris lumbricoides eggs are transmitted through contaminated food or water and hatch in the intestine. Juvenile larvae travel to the lungs and then to the pharynx, where they are swallowed and returned to the intestines to mature. These nematode roundworms cause ascariasis.
  • Enterobius vermicularis are nematode pinworms transmitted by the fecal-oral route. After ingestion, they travel to the colon where they cause enterobiasis.

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