COMPARATIVE EVALUATION OF COLISTIN SUSCEPTIBILITY TESTING METHODS AND THE RESISTANT PATTERN OF COLISTIN AMONG CARBAPENEM-RESISTANT Klebsiella pneumoniae ISOLATES IN A TERTIARY CARE SETUP

Abstract

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKp) infections remain a significant challenge associated with morbidity and mortality among patients worldwide. Colistin remains the mainstay for complicated CRKp. This study was done to relate the minimum inhibitory concentration (MIC) of colistin by gold standard technique broth microdilution (BMD) with automated system VITEK2C and its resistance pattern in CRKp strains to evaluate discrepancies and further course of action.

 Materials & Methods: This was a Cross sectional study, a total of 166 non repetitive isolates of CRKp was collected for a period of 18 months (September 2020 to March 2022). Phenotypic confirmatory test for detection of carbapenemases was done by Modified Hodge test and automation by VITEK 2C. Colistin MIC was determined by BMD (Mikrolatest^R, Erba^RMannheim) and VITEK 2C (Biomeriux) methods as per CLSI guidelines.

 Results: A total of 166 isolates of CRKp were studied.  89% of the isolates were susceptible to colistin by BMD whereas colistin resistance was 11% by BMD and 13% by VITEK2C and the range of MIC was between 4 and 16ug/ml.

 Conclusion: Broth Micro dilution (BMD) technique is gold standard method for determining the MIC of Colistin. The results correlated with Vitek 2C except for 3% of isolates which showed minor errors which indicates that for MIC values of colistin BMD is the preferred option. The high rate of resistance to carbapenems and colistin is worrisome. Nevertheless, the MIC of colistin helps the clinician to choose the drug in appropriate combinations.