Utility of a novel chromogenic medium as a screening method in the detection of carbapenemase producing Enterobacteriaceae

INTRODUCTION: With the emergence of multidrug resistant Gram-negative bugs, there is an urgent need for rapid detection of these resistant organisms. AIM: This study was performed to assess the utility of a novel chromogenic medium in the detection of carbapenemase producing Enterobacteriaceae from various clinical specimens. MATERIALS AND METHODS: A total of 202 isolates of Enterobacteriaceae, which were resistant to meropenem (10 μg) disc by standard disc diffusion method, were analyzed over a period of 6 months. These isolates were subjected to the modified Hodge test (MHT) and inoculated onto the chromogenic medium. Following which the results were analyzed. RESULTS: It was observed that 76.73% of the Enterobacteriaceae gave a positive result on the MHT, 18.31% were negative and 4.95% gave indeterminate result. While 88.11% produced growth on the chromogenic medium, 6.93% yielded no growth and 4.95% gave variable results. Concordance in the results of the two tests was found to be 65.34%. CONCLUSION: Enterobacteriaceae are emerging to be carbapenem resistant and are responsible for the soaring rates of Healthcare Associated Infections (HAIs), especially among critically ill patients. Hence, early detection of the same is important in controlling HAIs

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