Abstract
Background: Colistin is an antibiotic with lipophilic and hydrophilic properties, effective against Enterobacterales and non-fermenter bacteria. Due to the emergence of multidrug-resistant Gram-negative bacilli, colistin is being once again reintroduced as a last resort for their treatment. Resistance is caused by mutations and some are plasmid-mediated.

Aims and Objectives: The aim of the study was to determine antibiotic resistance patterns in Gram-negative bacilli and to detect colistin susceptibility patterns in multidrug-resistant Enterobacterales and Pseudomonas aeruginosa.

Materials and Methods: This prospective cross-sectional study was carried out in the Department of Microbiology, Calcutta National Medical College and Hospital, using standard laboratory protocol and colistin susceptibility was determined by colistin broth disk elution (CBDE) method.

Results: Out of a total of 80 patients infected with MDR isolates, 63.75% were male and 36.25% were female. The most common age group affected was 41–60 years. Multidrugresistant (MDR) bacteria were most commonly isolated from urine samples, and Klebsiella pneumoniae was the most common MDR bacteria isolated. Overall, colistin resistance was 7.5% and it was found most commonly in K. pneumoniae. The use of broad-spectrum antibiotics was the most common risk factor for the emergence of MDR bacterial infections, including colistin resistance.

Conclusion: The present study detects colistin resistance using a simple method – “CBDE test” which can be done in resource-poor settings and can guide clinicians to rationally use the medication as it may be used as an alternative treatment option for “Super bugs” and can even be used as the “last resort” in certain scenario.

Key words: Colistin; Colistin Broth Disk Elution; Multidrug-Resistant; Enterobacterales; Pseudomonas aeruginosa