Molecular Characterization and Antimicrobial Resistance Patterns of Multidrug-resistant Gram-negative Bacilli Isolated from Intensive Care Unit Patients in a Tertiary Care Hospital

Background: Multidrug-resistant (MDR) Gram-negative bacilli (GNB) present a critical challenge in intensive care units (ICUs), severely limiting therapeutic options. This study evaluated the prevalence and molecular resistance mechanisms of GNB in ICU patients. Introduction: Hospital-acquired urinary tract infections are among the most common healthcare-associated infections in ICUs. The emergence of MDR Gram-negative bacilli has reduced available treatment options and increased morbidity. This study aimed to evaluate antimicrobial resistance patterns and characterize major resistance genes among Gram-negative bacilli isolated from ICU patients. Materials and Methods: A hospital-based cross-sectional study was conducted from 2019 to 2022 across two tertiary centers in North India. We analyzed 427 non-duplicate MDR GNB isolates from ICU urinary samples. Identification followed standard biochemical protocols. Antimicrobial susceptibility testing was performed through Kirby–Bauer disk diffusion as per Clinical and Laboratory Standards Institute guidelines. Phenotypic detection of extended-spectrum β-lactamase (ESBL), AmpC, and carbapenemase production was performed, alongside molecular characterization of resistance genes (blaTEM, blaSHV, blaCTX-M, blaNDM, blaIMP, blaVIM, blaOXA). Results: In the present study, most isolates originated from the medical ICU (66.0%). Most MDR GNB isolates were from males (52%), and the majority of patients belonged to the age group > 60 years. The predominant isolates were Escherichia coli (60%), Klebsiella pneumoniae (19%), and Pseudomonas aeruginosa (12%). Alarmingly high resistance rates to Cephalosporins (>90%), Fluoroquinolones (>80%), and Carbapenems (70% overall) were observed. Overall, 40.9% of isolates were ESBL producers, 24.82% AmpC producers, and 13.81% Carbapenemase producers. Molecular analysis revealed a high prevalence of blaCTX M (100%), blaVIM (66%), and blaNDM (48%). Conclusion: The high prevalence of diverse resistance mechanisms underscores the impact of indiscriminate antimicrobial use. Implementation of stringent antimicrobial stewardship and robust infection control practices is essential to mitigate the spread of MDR pathogens in critical care settings.