Evaluation of phenotypic tests and screening markers for detection of metallo-β-lactamases in clinical isolates of Pseudomonas aeruginosa: A prospective study

Purpose: This study was conducted to estimate the prevalence of metallo-β-lactamases (MBL)-producing Pseudomonas aeruginosa isolates obtained from various clinical samples and to compare the diagnostic strength of different phenotypic MBL-detection tests and also to know the performance of ethylene diamine tetraacetic acid (EDTA) disk potentiation test (PT) which is the least studied. Materials and Methods: This study included 160 nonconsecutive isolates of P. aeruginosa collected over a period of 1-year. Resistance to carbapenems and ceftazidime was used for screening of isolates. Positively screened isolates were further subjected to five different MBL detecting phenotypic tests-MBL Epsilometer test (E-test), combined disk test (CDT), double-disk synergy test (DDST), EDTA disk PT using four cephalosporins and modified Hodge test (MHT). MBL E-test was considered as gold standard for MBL detection. Results: Based on the screening criteria for MBL production, 66 isolates were screened positive. The prevalence of MBL producing isolates of P. aeruginosa was 15% (24/160) based on E-test result. MHT showed the highest sensitivity (87.5%), followed by CDT (79.2%), while specificity was highest for DDST (100%), followed by PT (95.2%). Out of 24 MBL producers, 15 isolates (62.5%) were resistant to both imipenem (IPM) and meropenem. Conclusion: The early detection of MBL-producing P. aeruginosa may help inappropriate antimicrobial therapy and avoid the development and dissemination of these strains. Hence, routine detection of MBL production in P. aeruginosa should be undertaken. We recommend that all IPM and/meropenem-resistant P. aeruginosa isolates should be routinely screened for MBL production using CDT and the positive isolates may further be confirmed by MBL E-test or PCR. EDTA disk PT had low sensitivity