Evaluation of Xpert^® Carba-R Assay Performance from FecalSwab™ Samples

Background/Objectives: The emergence and spread of carbapenemase-producing Enterobacterales (CPE) represents a significant challenge prompting the need to optimize diagnostic tools to detect CPE carriers. The Xpert^® Carba-R assay (Cepheid, Sunnyvale, CA, USA), a Real-Time PCR-based test, can detect the bla_KPC, bla_VIM, bla_OXA-48, bla_NDM and bla_IMP carbapenemase genes directly from rectal swabs. This study assessed the performance of the Xpert^® Carba-R assay using FecalSwab™ (Copan, Brescia, Italy), a liquid-based collection device. Methods: The first part of the study aimed to establish the FecalSwab^TM volume which gave the most similar Ct values to those obtained by the Transystem™ double swab (Copan). The best volume was then used to assess the limit of detection (LoD) for each target and compare the accuracy of different FecalSwab^TM storage conditions (room temperature or 4 °C after 16 h compared to T₀). Results: The results indicated that using 200 µL of the FecalSwab™ medium provided reliable Ct values, with the lowest number of invalid samples compared to traditional methods. The average LoDs for different carbapenemases ranged from 4.7 × 10³ to 6.8 × 10³ CFU/mL. FecalSwab™ showed a better performance after 16 h at room temperature compared to storage at 4 °C. Conclusions: This study supports single sampling with the FecalSwab™ medium for both molecular and cultural methods, for the potential optimization of CPE screening.