The colistin testing and reporting quagmire in low and middle-income countries (LMIC)

Discrepancies in colistin resistance data was a major problem in India. The present study evaluated clinical isolates for colistin susceptibility using the Mikrolatest broth microdilution method and compared them with Vitek 2 Compact system. Categorical agreement was assessed using Custom-made Sensititre plates (Thermo Scientific) at the EUCAST Development laboratory Sweden, as the reference for Mikrolatest, and Mikrolatest was subsequently compared against Vitek 2 to determine accuracy and consistency across methods. Mikrolatest was initially validated against Sensititre using 34 multidrug-resistant Gram-negative isolates before comparison with Vitek 2. The study analysed 847 multidrug-resistant Gram-negative isolates, with a demographic profile skewed toward male patients (66.4%) and aged ≥50 year (82.4%). Urinary tract infections were the most common source of isolates (49.7%). Colistin testing, comparing the Mikrolatest broth microdilution method with the Vitek 2 Compact system, showed 93.15% categorical agreement; however, the study identified 54 very major errors. The higher rate of errors observed with the Vitek 2 Compact system indicates substantial discordance when compared with Mikrolatest and highlights the potential risk of false-positive sensitivity reporting in clinical practice. In contrast, the Mikrolatest broth microdilution kit provides an accurate, reliable, and accessible alternative for routine laboratory settings. Given the predominance of multidrug resistant K. pneumoniae in this study and the critical nature of colistin as a last-resort therapy, transitioning to a verified manual broth microdilution method is essential for robust antimicrobial stewardship. Hence, these findings support cautious interpretation of automated colistin susceptibility results and reinforce the importance of validated broth microdilution-based methods for accurate detection of colistin resistance.