Objective: Non-fermentative gram-negative bacilli (NFGNB) are frequently isolated from nosocomial infections in the recent years. Metallo-beta-lactamases (MBLs) are the enzymes that spread quickly and cause a wide spectrum of antibacterial resistance in Acinetobacter and Pseudomonas strains leading to serious problems in the treatment. Molecular and various phenotypic methods are used to determine the presence of MBLs. In this study, it was aimed to determine the production of MBLs enzyme by using four different phenotypic methods in imipenem-resistant Acinetobacter baumannii and Pseudomonas aeruginosa strains and also to compare the correlation between these methods.

Materials and Methods: This study was performed in Ataturk University, Research Hospital between September 2012 and October 2013. Carbapenem-resistant 94 A. baumannii and 48 P. aeruginosa strains which were obtained from 111 A. baumannii and 140 P. aeruginosa strains isolated from various clinical samples of different patients were analyzed in the study. The identification and the antimicrobial susceptibility determination of the isolates were done by VITEK-2 Compact automated system (bioMérieux, France). Phenotypic determination of the MBL production was done by double-disk synergy test, combined disc test, gradient strip test and modified Hodge test.

Results: MBL positivity of the A. baumannii strains detected by gradient strip test method, combined disk test, double-disk synergy test, and modified Hodge test were detected in 97.9, 98.9, 98.9, and 95.7% of the specimens, respectively. The corresponding rates were 100, 93.7, 89.6 and 41.7%, for the P. aeruginosa strains. The concordance of gradient strip test with combined disk test, double-disk synergy test, modified Hodge test were determined as 94.7, 94.7 and 91.5% respectively in A. baumannii strains and these concordance rates of gradient strip test between other tests were found to be 93.7, 89.6 and 41.7%, respectively in P. aeruginosa strains.

Conclusion: This study revealed a high carbapenem resistance and MBL production rates in A. baumannii and P. aeruginosa strains. The detection of MBLs provides epidemiological data that can be used for the selection of appropriate antimicrobial agents in the treatment of Acinetobacter and Pseudomonas infections. Although phenotypic methods used in this study to test the MBL production are generally in concordance with each other, molecular methods are necessary to determine the sensitivity and specificity of these tests.