Diagnostic accuracy of CHROMagar™ COL-APSE medium for the detection of colistin resistant Gram- negative rods directly from positive blood cultures
DOI:
https://doi.org/10.61529/idjp.v34i2.398Abstract
Background: A last-resort antibiotic for multidrug-resistant (MDR) Gram-negative rod (GNR) infections is colistin (polymyxin E). It causes cell lysis in Gram-negative bacteria by rupturing their outer membrane. The objective of this study is to determine the diagnostic accuracy of CHROMagarTM COL-APSE medium for the detection of colistin resistant Gram-negative rods by direct inoculation from positive blood cultures, keeping the standard blood culture and sensitivity testing method as the reference standard.
Material and Methods: This clinical diagnostic accuracy study was conducted at Department of Microbiology, Armed Forces Institute of Pathology, Rawalpindi from September 2024 to March 2025. The ability COL-APSE to directly identify colistin-resistant Gram-negative rods from positive blood cultures was evaluated. Following inoculation, samples were cultured for 18 to 24 hours at 37°C, and the outcomes were compared to CLSI 2024 criteria. Analysis of colony development and morphology showed how well the medium performed as a diagnostic tool in comparison to conventional blood culture and sensitivity testing techniques.
Results: When it came to identifying colistin-resistant Gram-negative rods, the COL-APSE medium showed 82.86% sensitivity, 52.99% specificity, and 69.26% diagnostic accuracy. Although it was able to detect, its ROC AUC of 0.679 (95% CI: 0.612–0.746) indicated a modest level of overall diagnostic performance but with low precision and limited identification power.
Conclusion: CHROMagar™ COL-APSE medium demonstrates restricted validity for direct detection of colistin-resistant Gram-negative rods from blood culture samples because of specific diagnostic optimization constraints.
Keywords: Colistin, Gram-negative bacteria, Gram-negative rods
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