Carbapenemase producing Gram Negative Bacilli (GNB) isolated from patients in a tertiary care hospital in South India – a prospective observational study.

Abstract

Background: Antimicrobial resistance (AMR) has emerged in the recent years amongst all the microbial organisms including gram-negative bacilli (GNB). Injudicious carbapenem usage for the treatment of multi drug resistant (MDR) GNB has subsequently led to the emergence of carbapenemase-producing GNB posing a serious threat to patient care. Objective: Determining the prevalence and profile of the carbapenemase producing gram negative bacilli using modified carbapenem inactivation method (mCIM) and Ethylenediamine tetra acetic acid CIM (eCIM) methods among patients attending a tertiary care hospital.

Material and methods: This study is a prospective laboratory based cross-sectional study. Antimicrobial Susceptibility testing (AST) was performed for all GNB isolates by Kirby-Bauer disc diffusion method. Organisms showing carbapenem resistance were subjected to mCIM for the detection of Carbapenemase production. Isolates positive for mCIM were further subjected to eCIM test to differentiate metallo-ß-lactamases from serine carbapenemases.

Results: 347 isolates were identified phenotypically as GNB. Amongst them, there were 77 carbapenem resistant isolates - Escherichia coli 24/77 (31.2%), Klebsiella pneumoniae 21/77 (27.2%) and Pseudomonas aeruginosa 21/77(27.2%) being the major isolates. Based on mCIM and eCIM assays, 46/77 (59.7%) isolates were metallo-beta-lactamase producers and 11/77 (14.3%) isolates were serine carbapenemase producers.

Conclusions: Understanding the carbapenem resistance mechanisms of GNB has important implications in devising treatment strategies. In the current study, the prevalence of carbapenem‑resistant GNB was 22.19% with E. coli, K. pneumoniae and P. aeruginosa being the three most predominant isolates. The findings were in concordance with similar studies across India.  Early diagnosis of the resistant isolates and prompt intervention is crucial in controlling the rates of resistant isolates.