Study to detect incidence of carbapenemase among Gram negative clinical isolates from tertiary care hospital

Abstract

Purpose:To study incidence of carbapenemases in teritary care hospital among gram negative clinical isolates of both Enterobacteriaceae and nonenterobactiaceae(nonferementers). Materials and Methods:A totalof 200 gram negative isolates were subjected to various phenotypic methods for carbapenemase detection along with minimum inhibitory concentration(MIC) for Imipenem and Meropenem by agar dilution technique.The phenotypic methods testedlike Double disc synergy test(DDST), Combined disc test (CDT), Modified hodge test(MHT). Results:Of 200 isolates,114 were members of famiy enterobacteriaceae and 86 were nonferementers.Out of 114, 71 were E.coli, 32 Klebsiella spp, 08 enterobacter and 03 citrobacter. Out of 86 nonfermenters 55 were pseudomonas spp and 31 were acinetobacter spp.Of the 200 isolates tested by DDST, 06 showed distortion of the one towards the EDTA disc.In CDT test 30 isolates showed an increase of >7mm zone of inhibition around the imipenem+EDTA disc in comparison to imipenem alone.Similarly 18 isolates had an increase of >7mm around the ceftazidime+EDTA in comparison to ceftazidime alone.Only one Klebsiella isolate was found to be positive with MHT,where a clover leaf shaped zone of inhibition was noted.Of 200 isolates, 167 were found to have an MIC of < 2µg/ml, 25 had an MIC value of 2µg/ml, 07 had an MIC of 4µg/ml and 01 had an MIC of 8µg/ml against imipenem. For meropenem, 170 isolates had an MIC of < 2µg/ml, 22 had an MIC of 2µg/ml, 07 had an MIC of 4µg/ml and 01 had an MIC of 8µg/ml. The strain, Klebsiella spp, showed higher MIC 8µg/ml for both imipenem and meropenem. Conclusions: Different phenotypic methods for detection of these carbapenemases are available, but controversies exist regarding the choice of optimal laboratory method. Molecular methods though expensive are the confirmatory tests