Abstract
In this prospective study, consecutive isolates of Klebsiella pneumoniae were tested for different mechanisms of carbapenem resistance using the modified Hodge test (MHT), Rosco Neo-Sensitabs (ROSCO). Phenylalanine arginine beta-naphthylamide assay (PABN) inhibitor-based test was done on isolates in which the mechanism of resistance was not identifiable by the ROSCO. Among 105 selected isolates, carbapenemase production was noted in 100 (95%) by MHT and ROSCO showed 97 (92·4%) inhibition with dipicolinic acid signifying the production of MBL. PCR amplification was positive in 90 (86%) isolates for blaNDM-1 and 46 (44%) isolates for blaOXA-48. 54 (51%) isolates were positive for blaCTX-M and all belonged to blaCTX-M group 1. Isolates co produced blaOXA-48 (31/105, 30%) and blaCTX-M (40/105, 38%) in combination with the carbapenemase (blaNDM-1) gene. Five colistin-resistant isolates were positive for blaOXA-48. Eight isolates did not show inhibition with any of the inhibitor containing disks and found to be positive for blaOXA-48. Isolates were tested for colistin-meropenem synergy and detection rate was higher by the checkerboard (48%) than E-test method (35%). Our study necessitates continuous surveillance to recognize the predominant machinery of resistance in a particular geographical region to formulate effective control measures.