Anaerobic gram negative rod. B. fragilis, B. distatonis, B. ovatus, B. thetaiotaomicron (these last three put the d-o-t- in DOT), B. gracilus, B. urolyticus, B. vulgatus.
A minor anaerobe (30 to 70% have it) but a major pathogen from the colon and really lousy teeth.
Usually part of a mixed infection where abscesses are found anywhere in the body. They require a lack of oxygen and/or dead meat to grow. B. fragilis can cause "marked abdominal pain and nonfebrile inflammatory diarrhea" due to an enterotoxin (PubMed).
Enterotoxigenic Bacteroides may be causal for bowel cancer (too early to be definitive) and Bacteroides in the blood may be associated with an underlying bowel adenocarcinoma (PubMed).
MDR B. fragilis is starting to rear its ugly head (PubMed), resistant to metronidazole, imipenem, piperacillin/tazobactam, clindamycin, cefotetan, ampicillin/sulbactam, and moxifloxacin also was observed..