Beta-lactams susceptibility testing of penicillin-resistant, ampicillin-susceptible Enterococcus faecalis isolates: a co
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nals of Clinical Microbiology and Antimicrobials Open Access
SHORT REPORT
Beta‑lactams susceptibility testing of penicillin‑resistant, ampicillin‑susceptible Enterococcus faecalis isolates: a comparative assessment of Etest and disk diffusion methods against broth dilution Natália Conceição1,2, Wellington Francisco Rodrigues3 , Kessys Lorrânya Peralta de Oliveira2, Lucas Emanuel Pinheiro da Silva1, Laís Rezende Cardoso de Souza1, Cristina da de Cunha Hueb Barata Oliveira4 and Adriana Gonçalves de Oliveira1,3*
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. Keywords: Enterococci, Etest, Disk diffusion, Beta-lactams, Piperacillin, Imipenem Background Although enterococci are widely distributed in the environment and are considered as normal intestinal microbes of humans and animals, during the past few decades, they have caused various infections in humans, primarily observed in hospitalized patients [1]. E. faecalis, an enterococci species, is most frequently isolated from clinical specimens [2]. These microorganisms are
*Correspondence: [email protected] 1 Instituto de Ciências Biológicas e Naturais, Universidade Federal do Triângulo Mineiro, Praça Manoel Terra, 330, 38015‑050, Uberaba, Minas Gerais, Brazil Full list of author information is available at the end of the article
intrinsically resistant to several antimicrobial agents and have a great ability to acquire and express new resistance determinants. Notably, in recent years, enterococci have acquired high-level antibiotic resistance to aminoglycosides, glycopeptides, and beta-lactams [1, 3]. Enterococci usually present cross-susceptibility to β-lactamase-susceptible penicillin; however, the emergence of clinical penicillin-resistant, ampicillin-susceptible Enterococcus faecalis (PRASEF) isolates, exhibiting an unusual resistance phenotype, have been reported in various countries [4–8]. Moreover, although the current Clinical and Laboratory Standards Institute (CLSI) [9] and European Committee on Antimicrobial Susceptibility Testing (EUCA
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