Validation of immunochromatographic test in broth-enriched rectal swab specimens

Rapid detection of Carbapenemase-Producing Enterobacterales (CPE) is essential for informing infection prevention and control actions to curb the spread of antimicrobial resistance. Immunochromatographic Tests (ICTs) offer a quick and cost-effective alternative to molecular methods but are typically designed for bacterial isolates rather than direct clinical specimens. We developed a protocol using the O.K.N.V.I. RESIST-5 ICT (Coris Bioconcept, Gembloux, Belgium) to detect KPC, NDM, OXA-48, VIM, and IMP carbapenemases from broth-enriched mock rectal swabs. A total of 35 well-characterized carbapenemase-producing isolates were inoculated into a 10 % stool matrix to create mock swabs. Swabs were incubated in Brain-Heart Infusion (BHI) broth, with and without a 10 μg meropenem disk, at 37 °C for 4 and 6 h. After incubation, broths were centrifuged, and pellets were tested using the ICT. Sensitivity, specificity, and accuracy were calculated for each method (with/without meropenem disk and incubation period). Optimal performance was achieved with swabs incubated in BHI broth without meropenem for 6 h, showing 100 % sensitivity, specificity, and accuracy for all the five enzymes tested. Incubation with meropenem or shorter incubation times resulted in lower sensitivities, with per-enzyme sensitivities ranging from 0 % to 100 %. The developed protocol enables rapid and accurate detection of five common carbapenemases directly from broth-enriched rectal swabs within 6 h. This method offers a practical alternative to culture-based and molecular techniques, potentially enhancing infection control measures through timely identification of CPE.