Characterization of carbapenem resistance mechanisms in Klebsiella pneumoniae and in vitro synergy of the colistin–meropenem combination

AbstractIn 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 fou...