A five-year multicenter study of the susceptibility of the Bacteroides fragilis group isolates to cephalosporins, cephamins, penicillins, clindamycin, and metronidazole in the United States

Abstract

Over 2800 clinical strains of the Bacteroides fragilis group were collected during a 5-year period from ten geographically separate sites and tested for their susceptibility to various antimicrobial agents using a broth microdilution method. Among the cephalosporins, ceftizoxime was the most active (13% resistance) and importantly exhibited relatively equal activity against both B. fragilis species and non-B. fragilis species. Cefotaxime exhibited similar activity with an overall resistance rate of 18%. Both ceftriaxone and cefoperazone were appreciably less active cephalosporins especially against non-B. fragilis species. With regard to cephamycins, cefoxitin (MIC90, 32 micrograms/ml) was more active than cefotetan (MIC90, > or = 256 micrograms/ml) and cefmetazole (MIC90, 64 micrograms/ml). Non-B. fragilis species were highly resistant to cefotetan and cefmetazole. Imipenem was highly active against all strains with the exception of four strains of B. fragilis. Ampicillin-sulbactam, amoxicillin-clavulanate, piperacillin-tazobactam, and cefoperazone-sulbactam were all highly active with resistance rates < 2%. No resistance was detected to metronidazole, whereas 14% of isolates were resistant to clindamycin. When compared with other studies, these findings underscore the wide variability in susceptibility patterns reported nationwide and the need to continue monitoring these patterns to aid in choosing the most active compounds for therapy.

Multicenter Survey of the Changing In Vitro Antimicrobial Susceptibilities of Clinical Isolates of Bacteroides fragilis Group, Prevotella, Fusobacterium, Porphyromonas , and Peptostreptococcus Species

“…fragilis species. However, the latter group exhibited more resistance (3,6,23) indicate the continued in vitro activity of metronidazole against the B. fragilis group species. However, Rotimi et al (20) reported clinical failures due to metronidazole-resistant isolates of the B. fragilis group and detected high-level cross-resistance to imipenem, meropenem, piperacillin, piperacillin-tazobactam, clindamycin, and cefoxitin.…”

In Vitro Susceptibilities of the Bacteroides fragilis Group Species: Change in Isolation Rates Significantly Affects Overall Susceptibility Data

“…The Anaerobe Working Group for the National Committee for Clinical Laboratory Standards (NCCLS) recommends that susceptibility testing of the B. fragilis group be done with a distribution of test isolates to approximate the species distribution normally isolated from infections (7). Several multicenter susceptibility studies have shown that the B. fragilis species comprises 58 to 63% of isolates (1,5,6,17). Such distribution rates have been relatively evident in studies reported during the 1980s and early 1990s.…”

“…The B. fragilis species unexplainably remains more susceptible to many antimicrobial agents than the other species within the group (1,7,17). It is therefore important, especially in the choice of empirical therapy, that sufficient susceptibility data from sufficient numbers of isolates be available for local or regional isolates.…”

“…The B. fragilis group is a heterogeneous group of species that vary in their susceptibility to antimicrobial agents, particularly ␤-lactams and clindamycin (1,12). The B. fragilis species unexplainably remains more susceptible to many antimicrobial agents than the other species within the group (1,7,17).…”

Emergence of Metronidazole-ResistantBacteroides fragilis, India

“…Published articles reveal only a few reported cases of B. fragilis that were resistant to metronidazole (6-10). Although the incidence of resistance to penicillin, cephalosporins, and clindamycin is increasing dramatically, no resistance to metronidazole in B. fragilis was found in some large-scale studies done throughout the world (11,12).…”