Effects of clindamycin and gentamicin and other antimicrobial combinations against enterococci in an experimental model of intra-abdominal abscess.

A model was developed to permit direct assessment of antibiotic efficacy against Enterococcus species in experimental intra-abdominal abscess. Abscesses yielded Enterococcus faecalis in pure culture. Antimicrobials were delivered by precisely controlled continuous intravenous infusion. After five days of therapy, ampicillin alone or in combination with gentamicin reduced residual bacterial titers from 7.93 +/- 1.05 (untreated) to 3.51 +/- 1.07 and 3.52 +/- 0.81 log10 colony forming units per gram, respectively. Both the clindamycin and gentamicin combination (6.49 +/- 1.33) and metronidazole and gentamicin combination (6.79 +/- 0.90) significantly suppressed the growth of enterococci (p less than 0.01). Combined clindamycin and aztreonam was ineffective, as were any of the agents used alone (except ampicillin). These results may explain, in part, the clinical efficacy of certain drug combinations against the enterococcal component of polymicrobial abscesses despite the apparent lack of in vitro activity of individual agents.