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

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 bla_NDM-1 and 46 (44%) isolates for bla_OXA-48. 54 (51%) isolates were positive for bla_CTX-M and all belonged to bla_CTX-M group 1. Isolates co produced bla_OXA-48 (31/105, 30%) and bla_CTX-M (40/105, 38%) in combination with the carbapenemase (bla_NDM-1) gene. Five colistin-resistant isolates were positive for bla_OXA-48. Eight isolates did not show inhibition with any of the inhibitor containing disks and found to be positive for bla_OXA-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.

Keywords:

• Carbapenem-resistant Klebsiella pneumoniae (CRKP)
• Colistin-meropenem
• In vitro synergy
• Modified Hodge test (MHT)