Major causes of gastrointestinal illness include Salmonella spp., Staphylococcus spp., Helicobacter pylori, Clostridium perfringens, Clostridium difficile, Bacillus cereus, and Yersinia bacteria. C. d...Major causes of gastrointestinal illness include Salmonella spp., Staphylococcus spp., Helicobacter pylori, Clostridium perfringens, Clostridium difficile, Bacillus cereus, and Yersinia bacteria. C. difficile is an important cause of hospital acquired infection. Vibrio cholerae causes cholera, which can be a severe diarrheal illness. Different strains of E. coli, including ETEC, EPEC, EIEC, and EHEC, cause different illnesses with varying degrees of severity.