In vitro activity of sulbactam plus ampicillin against hospital isolates of coagulase-negative staphylococci and Acinetobacter species.

The antimicrobial susceptibility of 54 recent clinical isolates of coagulase-negative slime- and non-slime-producing staphylococci and 52 Acinetobacter spp. to sulbactam, ampicillin and the combination of both drugs with a 1:1 ratio was studied by means of an agar dilution test. The coagulase-negative staphylococci showed resistance against sulbactam alone, whereas ampicillin as a single agent was nearly as active as sulbactam plus ampicillin (mode of MIC and MBC 0.03 and 4 mg/l vs. 1 mg/l; geometric mean of MIC and MBC 0.38 and 0.56 vs. 0.26 and 0.38 mg/l, respectively). Among slime-producing or non-slime-producing strains, there was no difference in the susceptibility against ampicillin alone compared to the sulbactam/ampicillin combination, with the exception of the higher MBC (mode: 4 mg/l) for slime-producing strains. Both ampicillin and the sulbactam/ampicillin combination were more active against non-slime-producing than slime-producing strains with modes of MIC and MBC of 0.03 vs. 1 or 4 mg/l. Acinetobacter spp. were susceptible to sulbactam alone (mode of MIC and MBC 1 mg/l; geometric mean of MIC and MBC 1.51 and 2.98, respectively), but resistant to ampicillin. However, the sulbactam/ampicillin combination was highly active against Acinetobacter spp. (mode of MIC and MBC 0.5 and 2 mg/l; geometric mean of MIC and MBC 0.74 and 2.08 mg/l, respectively).