Characterisation of carbapenemase-producing Gram-negative bacilli among clinical isolates in a tertiary care centre in Kerala, South India

Abstract

Background: Infections caused by carbapenem-resistant Gram-negative bacteria are a cause for concern due to the limited choice of antibiotics available for their treatment. Aims, Settings and Design: This study screened multidrug-resistant (MDR) Gram-negative bacilli isolated from clinical samples over a period of one year, for carbapenem resistance and characterised them using phenotypic methods such as combined disc diffusion test (CDDT), modified Hodge test (MHT), E-test for metallo-beta-lactamase (MBL) and molecular method, PCR. Materials and Methods: Two hundred and ten MDR Gram-negative bacilli were screened for carbapenem resistance using Imipenem and Meropenem disc diffusion. These were further checked for carbapenemase production by CDDT, MHT and E-test for MBL. Those positive by E-test were subjected to PCR. Uniplex PCR for New Delhi metallo-beta-lactamase-1 was used for Escherichia coli and Klebsiella pneumoniae , and multiplex PCR for Imipenemase and Verona imipenemase was used for Pseudomonas aeruginosa and Acinetobacter baumannii isolates. Results: Twenty-three (11%) isolates were found to be carbapenem-resistant and included E. coli (six) K. pneumoniae (three), P. aeruginosa (five) and A. baumannii (nine). Seventeen (74%) isolates were positive by phenotypic methods and were subjected to PCR. Out of eight Enterobacteriaceae isolates subjected to PCR, all were positive for bla NDM gene. All were negative for bla KPC gene. All five A. baumannii isolates subjected to PCR were found to contain bla VIM gene. Two out of four P. aeruginosa isolates were positive for bla IMP , one was positive for bla VIM gene. One P. aeruginosa isolate was positive for both bla IMP and bla VIM gene. Conclusions: In view of the increasing resistance of Gram-negative bacilli to carbapenems, rational use of antibiotics needs to be emphasised.