Comparative Evaluation of VITEK 2 and Broth Microdilution Methods for Colistin Antimicrobial Susceptibility Test

Aim:Accurate susceptibility testing methods are needed for colistin. In our study, we aimed to determine the efficacy of VITEK 2 (bioMérieux, Marcy-L’Etoile, France) in detecting colistin sensitivity by comparing the broth microdilution method with VITEK 2 automated system.Materials and Methods:We retrospectively compared VITEK 2 automated system and broth microdilution method for colistin sensitivity of various Gram-negative bacteria. The isolates were identified by conventional microbiological methods and VITEK 2 automated bacterial identification system.Results:The colistin susceptibility results of 104 Gram-negative microorganisms were compared, mostly from intensive care units (n = 56). When the broth microdilution method was taken as a reference, 7 very major errors (6.7%) and 4 major errors (3.8%) were determined in VITEK 2. The sensitivity was 92.9%, specificity was 20%, positive predictive value was 95.8%, negative predictive value was 12.5%.Conclusion:In our study, VITEK 2 could not meet the required criteria for the acceptance of the method due to the very major errors of 6.7% and the agreement of <90%. Although there are different results in many studies about the use of VITEK 2 in detecting the sensitivity of colistin, in our study did not meet the criteria for acceptance of the method.