Evaluation of the NG-Test MCR-1 Lateral Flow Assay and EDTA-Colistin Broth Disk Elution Methods To Detect Plasmid-Mediated Colistin Resistance Among Gram-Negative Bacterial Isolates

Plasmid-mediated colistin resistance (PMCR) is a global public health concern given its ease of transmissibility. The purpose of this study was to evaluate two methods for the detection of PMCR from bacterial colonies: 1) the NG-Test MCR-1 lateral flow immunoassay (NG Biotech, Guipry, France) and 2) the ethylenediaminetetraacetic acid-colistin broth disk elution (EDTA-CBDE) screening test method. These methods were evaluated using a cohort of contemporary, clinical Gram-negative bacilli isolates from 3 U.S. academic medical centers (126 Enterobacterales, 50 Pseudomonas aeruginosa and 50 Acinetobacter species; 1 mcr positive) and 12 mcr positive CDC–FDA AR bank isolates for which reference broth microdilution colistin susceptibility results were available. Eleven (4.6%) isolates were strongly positive by the MCR-1 LFA with an additional 8 (3.4%) isolates yielding faintly positive results. The positive percent agreement (PPA) and negative percent agreement (NPA) for MCR-1 detection was 100% and 96.1%, respectively. Upon repeat testing, only a single false-positive MCR-2 producer remained as the initial faint positives were negative. The EDTA-CBDE screen method had an overall PPA and NPA of 100% and 94.3%, respectively. The NPA was slightly lower at 94.2% with Enterobacterales compared to 96.0% with P. aeruginosa for EDTA-CBDE method. The MCR-1 LFA and EDTA-CBDE methods are both accurate and user-friendly methods for the detection of PMCR. Despite the rarity of PMCR among clinical isolates in the U.S., these methods are valuable tools that may be implemented in public health and clinical microbiology laboratories to further discern the mechanism of resistance among colistin-resistant Gram-negative isolates and to detect PMCR for infection prevention and control purposes.