Evaluation of Colistin Susceptibility among Multidrug-Resistant Gram- Negative Pathogens isolated from Blood Culture: Evidence from a Tertiary Care Setting in Delhi, India

Background: Antibiotic resistance is a grave threat to managing bloodstream infections, with MDRgram-negative pathogens like carbapenem-resistant Klebsiella pneumoniae and Escherichia coliescalating globally. This study sought to assess the colistin susceptibility profiles of MDR gram-negative clinical isolates obtained from blood cultures within a high-burden tertiary care facility inDelhi. Methods: This cross-sectional study was conducted in the Department of Microbiology at UCMS& GTB Hospital, Delhi, from January 2023 to June 2024. A total of 80 multidrug-resistant gram-negative clinical isolates from blood cultures were included. Carbapenem resistance was confirmedusing the Modified Carbapenem Inactivation Method (mCIM), while colistin resistance wasdetermined through Broth Microdilution Testing (BMD) Results: A study conducted over one year tested 80 Enterobacterales isolates, with 74 (92.5%)identified as CRE using the Kirby Bauer disc diffusion method and confirmed by mCIM testing. Themajority of isolates (44%) were from NICU, with a male predominance (60%). Enterobacter species(40%) was the most prevalent, followed by Klebsiella pneumoniae (26.6%), Citrobacter species(20%), and Escherichia coli (13.4%). The study found high multidrug resistance, with 100%resistance to most antibiotics in Enterobacter and Klebsiella species. All 74 isolates showedintermediate colistin susceptibility, with 43.2% exhibiting an MIC of 0.031 μg/mL. Conclusion: This study highlights the urgent need for colistin stewardship programs to address therise of CRE. The emergence of colistin resistance, especially in NICUs and ICUs, requires enhancedmonitoring and rapid diagnostics. Focusing on vulnerable populations like neonates and critically illpatients is crucial to combat multidrug-resistant infections.