Beta-lactams susceptibility testing of penicillin-resistant, ampicillin-susceptible Enterococcus faecalis isolates: a comparative assessment of Etest and disk diffusion methods against broth dilution

• Main Authors: Natália Conceição, Wellington Francisco Rodrigues, Kessys Lorrânya Peralta de Oliveira, Lucas Emanuel Pinheiro da Silva, Laís Rezende Cardoso de Souza, Cristina da de Cunha Hueb Barata Oliveira, Adriana Gonçalves de Oliveira
• Format: Article
• Language: English
• Published: BMC 2020-09-01
• Series: Annals of Clinical Microbiology and Antimicrobials
• Subjects: Enterococci; Etest; Disk diffusion; Beta-lactams; Piperacillin; Imipenem
• Online Access: http://link.springer.com/article/10.1186/s12941-020-00386-8

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.