GI Diarrhea and Others 1. Mechanisms Microorganisms that cause diarrhea attack specific areas of the intestine (Table 1). The upper small bowel is the site of attack by bacteria that produce toxins, such as Vibrio cholerae, E. coli and toxigenic food-poisoning bacteria (Staphylococcus aureus and Clostridium perfringens). Viruses such as Rotavirus and Norwalk Agent cause their greatest damage at this site as well. The large intestine is affected by bacteria that invade the bowel mucosa, such as Shigella and Campylobacter. The lower ileum is attacked preferentially by Salmonella and Yersinia. As a rule organisms that involve the upper small intestine produce fluid and electrolyte loss leading to dehydration; fever and systemic signs of infection are often absent. On the other hand, large bowel pathogens cause fever, abdominal pain and bloody, mucoid, low-volume diarrheal stools. 2. E.coli diarrhea pathogens Five types of E. coli have been recognized as pathogens in the intestinal tract. Each causes
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