Comparison of Different Methods for In Vitro Susceptibility Testing of Colistin in Gram-Negative Bacilli Isolated from a Tertiary Care Hospital

Dr. Nishikanta Sahoo

Abstract: Background: The global rise in antimicrobial resistance has necessitated the reintroduction of colistin as a last-resort antimicrobial agent against multidrug-resistant Gram-negative bacilli. Accurate laboratory determination of colistin susceptibility remains challenging due to methodological limitations. Objectives: To compare the performance of colistin broth disc elution (CBDE) and E-test methods with broth microdilution (BMD), the reference standard, for detection of colistin resistance among Gram-negative bacilli. Methods: A laboratory-based, cross-sectional, comparative study was conducted over one year in a tertiary care hospital. Clinical samples from admitted patients were processed using standard microbiological techniques. Colistin susceptibility testing was performed using BMD, CBDE, and E-test. Categorical agreement of CBDE and E-test was calculated against BMD. Results: Of 456 Gram-negative bacilli isolated, 57 (12.5%) were colistin-resistant by BMD. Klebsiella pneumoniae was the predominant resistant organism. CBDE showed a high categorical agreement with BMD (94.7%), whereas E-test showed lower agreement (86.0%). Conclusion: Broth microdilution remains the gold standard for colistin susceptibility testing. CBDE is a reliable and cost-effective alternative suitable for routine diagnostic laboratories, while E-test results should be interpreted with caution.

Keywords: Colistin, Gram-negative bacilli, Broth microdilution, Colistin broth disc elution, Antimicrobial resistance

How to Cite?: Dr. Nishikanta Sahoo, "Comparison of Different Methods for In Vitro Susceptibility Testing of Colistin in Gram-Negative Bacilli Isolated from a Tertiary Care Hospital", Volume 14 Issue 12, December 2025, International Journal of Science and Research (IJSR), Pages: 1624-1625, https://www.ijsr.net/getabstract.php?paperid=MR251220074438, DOI: https://dx.doi.org/10.21275/MR251220074438