International Journal of Medical Discoveries

Background: Colistin, discovered in the 1940s, was initially used as a broad-spectrum antibiotic against gram-negative bacteria. Due to its significant nephrotoxic and neurotoxic effects, its systemic use declined in the 1970s. However, colistin has re-emerged as a critical therapeutic option with the increasing prevalence of multidrug-resistant pathogens, particularly those producing carbapenemases and extended-spectrum beta-lactamases.
Objective: This study aimed to evaluate colistin susceptibility in panresistant Enterobacterales, Acinetobacter, and Pseudomonas species using the broth microdilution method.
Methods: A total of 124 non-duplicate clinical isolates were collected from March 2021 to April 2023, including Klebsiella pneumoniae (52%), Acinetobacter baumannii (35%), Escherichia coli (6%), Pseudomonas aeruginosa (6%), Acinetobacter jejunii (2%), and Klebsiella oxytoca (1%). Patient samples were obtained from various hospital units. Colistin susceptibility testing was performed using the CLSI-EUCAST 2016 guidelines, following the broth microdilution method. MIC values ≤2 µg/ml were considered susceptible, and ≥4 µg/ml resistant.
Results: Out of 124 isolates, 77 (62.1%) were colistin-susceptible, and 47 (37.9%) were resistant. Resistance rates among key species were: K. pneumoniae (39.1%), A. baumannii (30.2%), E. coli (28.6%), and P. aeruginosa (85.7%). Resistant isolates were identified in urine (8.1%), blood (14.5%), and respiratory samples (4.8%).
Conclusion: Colistin remains a valuable therapeutic agent against multidrug-resistant gram-negative bacteria. Routine susceptibility testing is essential to guide appropriate use and prevent the emergence of further resistance.