THE STUDY OF COLISTIN SUSCEPTIBILITY AMONG CARBAPENEM-RESISTANT GRAM-NEGATIVE BACILLI BY BROTH MICRODILUTION METHOD USING READY-TO-USE COLISTIN MIC PLATE KIT

K. SNEHITHA; S. SWAPNA; P. RATNAKUMARI

doi:10.22159/ijcpr.2025v17i4.7037

Authors

K. SNEHITHA Department of Microbiology, Andhra Medical College, Visakhapatnam, India https://orcid.org/0009-0004-7425-2355
S. SWAPNA Department of Microbiology, Andhra Medical College, Visakhapatnam, India https://orcid.org/0009-0005-8863-5039
P. RATNAKUMARI Department of Microbiology, Andhra Medical College, Visakhapatnam, India https://orcid.org/0009-0003-5061-3665

DOI:

https://doi.org/10.22159/ijcpr.2025v17i4.7037

Keywords:

Carbapenem Resistance, EUCAST, Colistin, Broth Micro Dilution, Ready-to-use

Abstract

Objective: Carbapenem-resistant Gram-negative bacteria (CR-GNB) pose a major threat to the treatment of infectious diseases. There is a recent increase of Colistin use as a last resort antibiotic for carbapenem-resistant and extensively drug-resistant GNB infections. As per EUCAST (2023) and CLSI(2023) guidelines, gradient diffusion or disc diffusion are inappropriate for colistin susceptibility testing and colistin MIC should be performed by broth microdilution method.

The aim of the present study is to isolate Carbapenem-resistant Gram-negative bacilli (CR-GNB) and to detect colistin susceptibility in CR-GNB using commercial broth microdilution plate kit.

Methods: This is a cross-sectional descriptive study conducted at the Department of Microbiology, Andhra Medical College, Visakhapatnam, for a period of 6 mo from October 2023 to March 2024. A total of 58 CR-GNB isolated from 4905 samples were taken for colistin susceptibility testing by the HiMIC plate kit Broth microdilution technique.

Results: This study examined 4905 clinical samples comprising of Urines, Blood, and Exudates. Out of which 1269 were GNB, 41 were Gram-positive cocci and 3595 were sterile. Of these, 1269 GNB, 58 were identified as CR-GNB, according to EUCAST (2023) guidelines. The most common CR-GNB organism isolated was Klebsiella spp. (47%), followed by Escherichia coli (41%), Acinetobacter spp. (7%), and Pseudomonas aeruginosa (5%). All 58 isolates were tested for colistin susceptibility, with 4 isolates showing resistance and 54 being in the sensitive range according to EUCAST guidelines. Of the colistin-resistant isolates, 3 were Klebsiella spp. and 1 was E. coli with MICs of 16 mcg/ml, 16 mcg/ml, 8 mcg/ml, and 4 mcg/ml, respectively.

Conclusion: This colistin plate kit is a high-throughput, less time-consuming, ready-to-use method for colistin susceptibility testing in routine microbiology laboratories, which guides clinicians in lowering mortality and morbidity of CR-GNB infections by appropriate use of colistin.

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