Optimization of the rapid carbapenem inactivation method for use with AmpC hyperproducers

Area of Science:

• Clinical microbiology
• Antimicrobial resistance
• Diagnostic test development

Background:

• Carbapenemase-producing Enterobacterales (CPEs) pose a significant threat due to limited treatment options.
• Distinguishing CPEs from AmpC-hyperproducing Enterobacterales (AHEs) is challenging as AHEs can mimic CPEs in standard tests.
• Accurate and rapid detection methods are crucial for infection control and patient management.

Purpose of the Study:

• To develop and evaluate a modified rapid Carbapenem Inactivation Method (rCIM-A) for accurate differentiation between AHEs and CPEs.
• To assess the performance of rCIM-A compared to the standard rCIM and Carba NP tests.
• To improve the specificity of CPE detection in clinical settings.

Main Methods:

• The study evaluated 249 Enterobacterales isolates, including AHEs, CPEs, and control strains.
• A novel rCIM-A method was developed, incorporating cloxacillin into the initial incubation step of the standard rCIM.
• Performance metrics (sensitivity, specificity) were compared across rCIM-A, rCIM, and Carba NP tests.

Main Results:

• The rCIM-A achieved a sensitivity of 84.26% and a specificity of 99.29% for CPE detection.
• Compared to rCIM (86.11% sensitivity, 80.85% specificity) and Carba NP (84.04% sensitivity, 91.37% specificity), rCIM-A showed significantly improved specificity for AHEs.
• While effective, rCIM-A had limitations in detecting certain carbapenemases like OXA-23 and some MBLs, and one AmpC variant (MIR-10) yielded false positives.

Conclusions:

• The rCIM-A significantly enhances specificity for differentiating AHEs from CPEs without compromising performance for other resistance mechanisms.
• This optimized method is a cheap, easy, rapid, and accurate alternative for CPE detection, potentially replacing the standard rCIM.
• Further refinement may be needed for specific carbapenemase types and certain AmpC variants to ensure comprehensive detection.