Colistin Susceptibility Patterns in Multidrug-Resistant Gram-Negative Bacteria Isolated from Urine Samples at a Tertiary Care Hospital

Background: The study aimed to determine the colistin susceptibility profile among multidrug-resistant Gram-negative bacteria from patients with UTI. Materials and Methods: A prospective study was conducted for 9 months. In total, 60 urine samples were screened for Gram-negative bacteria. Isolates were subjected to antimicrobial susceptibility testing through the Kirby-Bauer method. Colistin susceptibility was determined through the E-test method.Results: In this study, 60 multidrug-resistant isolates were obtained from May 2022-Jan 2023 from urine samples received in the microbiology department, SRMMCH and Research Center for routine diagnosis. Among them, 75% were Escherichia coli, 15% were Klebsiella pneumonia, 6.6% were Pseudomonas spp and 3.3% were Proteus spp. All study isolates were resistant to ampicillin, cefoxitin, ceftriaxone, ceftazidime, and cefepime. For colistin, 90% of the isolates showed intermediate resistance and 10% showed complete resistance. Conclusion: This study documented 100% non-susceptibility to colistin among Gram-negative bacteria from urine samples. Notably, 60% of the strains were ESBL producers followed by 40% of AmpC producers. This study highlights the fact that the colistin non-susceptibility was higher among Gram-negative bacteria in UTI.