Prevalence of Carbapenem Resistant Non-Fermenting Gram Negative Bacterial Infection and Identification of Carbapenemase Producing NFGNB Isolates by Simple Phenotypic Tests.

INTRODUCTION: Non-Fermenting Gram negative bacilli (NFGNB) are emerging multi-drug resistant pathogens causing nosocomial infections. In recent years, carbapenem resistance in NFGNB has increased due to a variety of drug resistance mechanisms, the most common being production of carbapenemases.

AIM: To detect carbapenemase and metallo-β-lactamase (MBL) production in NFGNBs by four phenotypic tests and to compare the various phenotypic methods for detection of carbapenemase and MBL production in nosocomial NFGNB isolates.

MATERIALS AND METHODS: It is a cross sectional study carried out in the department of Microbiology, Chennai Medical College Hospital and Research Center, Irungalur, Trichy between January 2015 and December 2015. Out of the 598 NFGNB isolated from all the 5402 heterogenous clinical samples that were processed, 52 (8.7%) NFGNB showed resistance or intermediate sensitivity to meropenem as tested by disc diffusion assay. All the 52 isolates were subjected to four different phenotypic tests for carbapenemase and MBL detection, which included Modified Hodge Test (MHT), Meropenem-EDTA Disc Synergy (EDS) test, Meropenem-EDTA Combined Disc Test (CDT) and Growth on CHROMagar KPC.

RESULTS: Among the 52 isolates, 29 (55.77%) were MHT positive and 49 (94.23%) were positive for growth on CHROMEagar KPC which were identified as carbapenemase producers. 44 (84.61%) were EDS positive and 46 (88.46%) were CDT positive which were identified as metallo-β-lactamase producers.

CONCLUSION: The presence of these resistant bugs strongly suggests the need to prevent their further spread by implementation of strict infection control measures and regular surveillance to check their outcome. Growth on CHROMagar KPC is the test that has picked up more number of carbapenem resistant isolates as carbapenemase and metallo-β-lactamase producers among the four tests. It is also cheap and easy to perform, making it the most reliable test for routine screening of carbapenemase and MBL producers in clinical laboratories.