The role of Bacteroides fragilis in the pathogenesis of acute appendicitis.

The predominant bacteria from 50 inflamed human appendices were isolated. Anaerobic bacteria were isolated more frequently than aerobic bacteria ( 141 versus 96 isolates). E. coli was the most common aerobic genus (47 out of 50 patients). Bacteria belonging to the B. fragilis groups (B. Fragilis, B. ovatus, B. distasonis, B. thetaiotaomicron, B. vulgatus and B. uniformis) were the most frequently isolated anaerobic microorganisms (87 of 141 strains), and B. fragilis predominated within this group (24 out of 87 strains). There were no significant differences in the numbers and types of bacteria found in three patients groups (Group A--19 phlegmonous; Group B--19 gangrenous; and Group C--12 perforative appendicitis cases). Serological investigations of the humoral antibody responses (IFL) against the predominant bacteria in the three patient groups showed that a doubling, or more, of the titer was observed in the following cases: against B. fragilis, 3 out of 8 patients (Group A); 5 out of 7 patients (Group B); and 7 out of 7 patients (Group C). The corresponding figures for E. coli were 4 out of 18, 3 out of 17, and 5 out of 12 patients. Only minor responses against the remaining aerobic and anaerobic isolates were measured. From the bacteriological and immunological results we conclude that (1) the B. fragilis group were the predominant bacteria in diseased appendices; (2) that significant antibody responses were only observed against B. fragilis; (3) that the response increased with the degree of organ destruction and the length of time elapsed from the onset of the symptoms; (4) that B. fragilis is likely to play an important role in the pathogenesis of acute appendicitis, provided that other predisposing factors, such as a deterioration of the blood circulation in the appendiceal wall, are present.