Evolution of antimicrobial susceptibility in isolates of the Bacteroides fragilis group in Spain.

The species included in the Bacteroides fragilis group are the most frequent nontoxigenic anaerobic bacteria pathogenic to humans. The emergence and increase of resistance to antibiotics among this group make surveillance and state-of-the-art knowledge important. We studied the evolution of resistance to antibiotics in B. fragilis group organisms isolated at the University Clinical Hospital at Salamanca, Spain, from 1975 to 1987. No resistance to imipenem, chloramphenicol, or metronidazole was detected. The frequency of resistance to clindamycin was in the range of 6%-7%. Resistance to moxalactam, cefoxitin, mezlocillin, and piperacillin has increased steadily and is currently approximately 20%-25%.