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: (i) the NG-Test MCR-1 lateral flow immunoassay (LFA; NG Biotech, Guipry, France) and (ii) the EDTA-colistin broth disk elution (EDTA-CBDE) screening test method. These methods were evaluated using a cohort of contemporary, clinical Gram-negative bacillus isolates from 3 U.S. academic medical centers (126 isolates of the Enterobacterales, 50 Pseudomonas aeruginosa isolates, and 50 Acinetobacter species isolates; 1 isolate was mcr positive) and 12 mcr-positive CDC-FDA Antibiotic Resistance (AR) Isolate 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 were 100% and 96.1%, respectively. Upon repeat testing, only a single false-positive MCR-2 producer remained, as the isolates with initially faintly positive results were negative. The EDTA-CBDE screening method had an overall PPA and NPA of 100% and 94.3%, respectively. The NPA for the EDTA-CBDE method was slightly lower at 94.2% with Enterobacterales, whereas it was 96.0% with P. aeruginosa. 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 United States, 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.

No abstract

Background In 2019, the United States Food and Drug Administration published its final recommendations to mitigate bacterial contamination of platelets. We sought to evaluate our secondary bacterial culture (SBC) strategy in light of those recommendations. Study Design and Methods A retrospective analysis was conducted of SBC data (October 2016‐2019) at our institution. SBC was performed upon receipt (Day 3 after collection); 5 mL of platelet product was inoculated aseptically into an aerobic bottle and incubated at 35°C for 3 days. For 8 months, a 10‐mL inoculum was trialed. No quarantine was applied. All positive cultures underwent Gram staining and repeat culture of the platelet product (if available). A probable true positive was defined as concordant positive culture between the initial and repeat culture. The incidence of probable true‐ and false‐positive cultures were reported descriptively and differences evaluated by sampling volume. Results Over 3 years, 55 896 platelet products underwent SBC, yielding 30 initial positive results (approx. 1/1863 platelets); 25 (83.3%) signaled within 24 hours of SBC. The rates of probable true positive, false positive, and indeterminate for 5 mL were 0.027% (1/3771), 0.002% (1/45 251) and 0.018% (1/5656), respectively. The respective rates for 10 mL were 0.018% (1/5323), 0.07% (1/1521), and 0%. Seven of eight (87.5%) false‐positive SBCs occurred with a 10‐mL inoculum. No septic transfusion reactions were reported. Conclusion SBC continues to interdict bacterially contaminated units of platelets. Our findings suggest higher rates of false positivity using large‐volume inocula.