Evaluation of Six Commercial and Non-Commercial Colistin Resistance Diagnostics

Abstract

Background. Resistance to colistin, a last-reserve antibiotic used for treating drug-resistant infections, is increasing globally. This study evaluated six diagnostic tests designed to detect colistin-resistant pathogens. Methods. PCR and broth microdilution assays (BMD) were used to respectively characterize the molecular mechanisms and phenotypic colistin resistance of 142 Gram-negative bacterial isolates and controls. The sensitivity, specificity, positive- and negative-predictive values, major (ME) and very major errors (VME), categorical and essential agreements (EA) of ComASP Colistin, CHROMagar COL-APSE, Rapid NP Test, Sensititre, MicroScan, and Vitek 2 were determined with these isolates; the BMD was used as gold standard. Results. The Vitek 2, Sensititre, and ComASP tests were more efficient, albeit with concerning ME and VMEs and low EAs. Sensititre was 100% specific with 0% ME and 3.61% VME; Vitek 2 had the least VME (1.25% and 0%) and a low EA (57.50%). ComASP had an EA of 75.35%. MicroScan was highly sensitive (96.55%) but less specific (87.50%), with very below-accetable EAs (48.11%). The CHROMAgar COL-APSE efficiently identified the species with their unique colours but was the least specific (67.80%), with the highest ME (32.20%) and high VME (7.23%). The Rapid NP test had the highest VME (7.84%), producing results within 4 hours with 92.16% sensitivity and 96.08% specificity. Conclusion: Vitek 2, MicroScan, ComASP colistin, and Sensititre are good for determining colistin resistance; the latter two tests are recommendable for low-resourced laboratories. The in-house Rapid NP test has short turnaround time with high efficiency for initial resistance screening.