ABSTRACT
This study aimed to evaluate the accuracy of disk diffusion and Etest methods, compared to that of the broth dilution reference method for identifying beta-lactam susceptibilities of Penicillin-Resistant, Ampicillin-Susceptible Enterococcus faecalis (PRASEF) isolates. Fifty-nine PRASEF and 15 Penicillin-Susceptible, Ampicillin-Susceptible E. faecalis (PSASEF) clinical nonrepetitive isolates were evaluated. The effectiveness of five beta-lactams (ampicillin, amoxicillin, imipenem, penicillin, and piperacillin) was tested. All antimicrobial susceptibility tests were performed and interpreted according to the Clinical and Laboratory Standards Institute guidelines. Interpretative discrepancies, such as essential agreement, categorical agreement, and errors, were assessed. The acceptability was ≥ 90% for both categorical agreement and essential agreement. Etest proved to be an accurate method for testing beta-lactam susceptibilities of the emerging PRASEF isolates, disk diffusion presented poor performance, particularly for imipenem and piperacillin.
Subject(s)
Disk Diffusion Antimicrobial Tests/methods , Enterococcus faecalis/drug effects , Microbial Sensitivity Tests/methods , beta-Lactams/pharmacology , Amoxicillin/pharmacology , Ampicillin/pharmacology , Anti-Bacterial Agents/pharmacology , Drug Resistance, Multiple, Bacterial , Humans , Imipenem/pharmacology , Penicillins/pharmacology , Piperacillin/pharmacology , Sensitivity and SpecificityABSTRACT
Our findings demonstrated that the results obtained for ampicillin may accurately predict the in vitro susceptibility to amoxicillin but not to imipenem and piperacillin among isolates of Enterococcus faecalis resistant to penicillin but susceptible to ampicillin, which have emerged recently, in contrast to penicillin- and ampicillin-susceptible isolates.