In-vitro activity of amoxycillin and ticarcillin in combination with clavulanic acid compared with that of new β-lactam agents against species of the Bacteroides fragilis group

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Abstract
One hundred and one isolates representing five species of the Bacteroides fragilis group were examined for their susceptibility to amoxycillin and ticarcillin alone or in combination with clavulanic acid, as well as to cefoxitin, latamoxef (moxalactam), ceftizoxime, imipenem, chloramphenicol, clindamycin and metronidazole by the proposed NCCLS agar dilution method. Bactericidal activity of amoxycillin, ticarcillin, combinations of amoxycillin-clavulanic acid and ticarcillin-clavulanic acid, cefoxitin and latamoxef against 54 strains was further assessed by a dilution test in broth. The most active agents were imipenem and the combinations of amoxycillin-clavulanic acid and ticarcillin-clavulanic acid. MIC results indicated that Bacteroides fragilis and B. vulgatus were more susceptible to β-lactams than were B. distasonis, B. ovatus and B. thetaiotaomicron. Clavulanic acid greatly potentiated the activity of amoxycillin and ticarcillin against the 94 β-lactamase positive strains but had no effect on the seven B. distasonis isolates that were β-lactamase negative. Synergistic bactericidal activities could be observed by the amoxycillin-clavulanic and ticarcillin-clavulanic combinations.