Colistin Susceptibility Testing by Colistin Broth Disk Elution MIC Method among Carbapenem-resistant Gram-negative Blood Culture Clinical Isolates in a Tertiary Care Setting, East Delhi, India

Background: Antibiotic resistance is a growing concern for bloodstream infections (BSIs), especially with the emergence of multidrug- resistant (MDR) gram-negative bacteria. In this study, we aimed to assess the pattern of colistin susceptibility using the colistin broth disc elution (CBDE) method among carbapenem-resistant gram-negative clinical isolates from blood cultures in a high burden tertiary healthcare setting in East Delhi. Methods: A total of 106 carbapenem-resistant gram-negative clinical isolates were tested. The most common isolates were Klebsiella pneumoniae, Escherichia coli, Enterobacter species, and Klebsiella oxytoca by CBDE method. Results: All the carbapenem resistant gram- negative bacterial blood culture isolates showed intermediate colistin susceptibility. This was statistically significant by chi-square test (p<0.5). Conclusion: This study highlights the need to monitor colistin resistance trends in the face of increasing antimicrobial resistance. Accurate surveillance of emerging colistin resistance is crucial for effective management of BSIs caused by carbapenem- resistant gram-negative bacteria.