Objective: Although routine investigation of the presence of the ESBL is not recommended in the new CLSI and EUCAST guidelines, it is recommended to test ESBL as a part of infection control and for epidemiological purposes. The aim of this study was to compare Disk Approximation Method (DAM) and VITEK 2 (bioMérieux, France) fully automated test system fort he determination of ESBL in Escherichia coli and Klebsiella pneumoniae strains.

Materials and Methods: A total of 95 E.coli and 61 K. pneumoniae strains isolated from various clinical specimens in 2014 were included in the study. The antibiotic susceptibility testing of the isolates were previously performed by VITEK 2 system. DAM was performed on the strains which were grown from the stock series. Six K. pneumoniae and two E. coli strains which were ESBL (+) with VITEK 2, were found to be resistant to all antibiotics with DAM and these isolates were not assessed.

Results: One E. coli and three K. pneumoniae strains were found ESBL negative with VITEK-2, but were positive with DAM, twelve E. coli and four K. pneumoniae strains were found ESBL positive with VITEK-2, but were negative with DAM. Sensitivity, specificity, false positive, false negative and accuracy rates of VITEK-2 were 93.3%, 81.8%, 18.1%, 6.6% and 86.4% respectively when DAM was accepted as the gold standard test.

Conclusion: According to the data obtained in this study it was concluded that although VITEK 2 automated system yielded false negative and false positive results, it revealed high sensitivity and specificity for ESBL detection. However, since automated systems are not considered as reference methods, discordant ESBL results should be verified with a second test.