Antibiotic Susceptibility of Enterococcal Strains: Comparison of Clinical Breakpoint Interpretations for Disk Diffusion According to the CLSI and EUCAST

Abstract

Objective: Our aim in this study is to compare the Clinical Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria, which were started to be used in Ahi Evran University Training and Research Hospital, Medical Microbiology Laboratory, as of January 2016, in terms of antibiotic susceptibility results of enterococcal strains isolated from clinical specimens, and determine their possible effects to our reportings. Methods: A total of 77 enterococcal strains isolated from various clinical specimens were included in this study. Manual methods and the VITEK (R) 2 (bioMerieux, Marcy l'Etoile, France) automated system were used for identification of strains. Antibiotic susceptibilities of strains were determined by standard disk diffusion method. Zone diameters determined according to antibiotic susceptibility tests of strains were evaluated and compared according to the CLSI and EUCAST guidelines. Results: There was a significant difference between streptomycin (300 mu g) and quinupristin-dalfopristin (15 mu g) disks in terms of antibiotic susceptibilities of the strains in the evaluation based on both guidelines (p<0.05). Significant differences were not detected among other antibiotics (ampicillin, linezolid, norfloxacin, teicoplanin, vancomycin, gentamicin and nitrofurantoin). Conclusions: One of the most important tasks of the medical microbiology laboratories is to perform and interpret antibiotic susceptibility tests in line with current information. Also clinicians need to be aware of possible effects of changes in antibiotic susceptibility ratios along with the transition to the EUCAST guideline.