Why is Bacteroides fragilis considered an opportunistic pathogen?
The Bacteroides genus comprise the majority of microorganisms that inhabit the digestive tract. 50% of most fecal matter is actually Bacteroides fragilis cells. Bacteroides organisms are the anaerobic counterpart of E. coli except they are somewhat smaller. They grow well on blood agar, and under the microscope, they may contain large vacuoles that are similar in appearance to spores. Members of Bacteroides species are not spore-forming, but they do produce a very large capsule. Their pathogenicity is limited, however, because they possess no endotoxin in their cell membrane. Bacteroides fragilis is primarily associated with infections of the peritoneal cavity. B. fragilis is not overtly invasive, but is capable of participating in intraabdominal infections in the event the mucosal wall of the intestine being disrupted. Incidences during which Bacteroides infections may be initiated include gastrointestinal surgery, perforated or gangrenous appendicitis, perforated ulcer, diverticuliti
