In vitro susceptibilities of Escherichia coli and Klebsiella spp. to ampicillin-sulbactam and amoxicillin-clavulanic acid.

Ampicillin-sulbactam (A/S) and amoxicillin-clavulanic acid (AUG) are thought to be equally efficacious clinically against the Enterobacteriaceae family. In this study, the in vitro activities of the A/S and AUG were evaluated and compared against Escherichia coli and Klebsiella spp. Antimicrobial susceptibility tests were performed by standard agar dilution and disc diffusion techniques according to the Clinical and Laboratory Standards Institute (CLSI). During the study period, 973 strains were isolated. Of the 973 bacteria isolated, 823 were E. coli and 150 Klebsiella spp. More organisms were found to be susceptible to AUG than A/S, regardless of the susceptibility testing methodology. The agar dilution results of the isolates that were found to be sensitive or resistant were also compatible with the disc diffusion results. However, some differences were seen in the agar dilution results of some isolates that were found to be intermediately resistant with disc diffusion. In E. coli isolates, 17 of the 76 AUG intermediately resistant isolates (by disc diffusion), and 17 of the 63 A/S intermediately resistant isolates (by disc diffusion) showed different resistant patterns by agar dilution. When the CLSI breakpoint criteria are applied it should be considered that AUG and A/S sensitivity in E. coli and Klebsiella spp. strains may show differences.