Evaluation of new expert rules for the detection and differentiation of carbapenemase-producing Enterobacterales within the French epidemiological context

ABSTRACT The increasing prevalence of carbapenemase-producing Enterobacterales (CPE) requires reliable diagnostic tools. This study evaluated the performance of the VITEK2 Advanced Expert System, a software interpretation program combined with VITEK2 AST results, for CPE detection, and the ability of BIOART expert rules to identify carbapenemase types. Antimicrobial susceptibility testing was performed using VITEK2 (N436 + XN28 cards) and disk diffusion on a collection of 244 isolates representative of French epidemiology, including 145 CPE, 51 non-CPE carbapenem-resistant Enterobacterales (CRE), and 48 non-CRE. A dedicated OXA-244/484 rule was assessed on a collection of 36 OXA-244/484 producers, known to be difficult to detect. The VITEK2 N436/AES and CA-SFM algorithm demonstrated similar sensitivities (93.8% vs 97.2%) and specificities (53.5% vs 49.5%) for CPE detection. Most detection errors involved OXA-244/484 producers. Application of the dedicated OXA-244/484 rule enabled 100% detection. BIOART rules identified the single carbapenemase class with no other mechanism reported in 83 cases, the correct class with additional mechanisms reported in 30 cases, and no carbapenemase class, or an incorrect carbapenemase class were assigned in 6 and 5 cases, respectively. Twelve isolates were outside the scope of BIOART rule (IMI or multiple carbapenemases). Single correct carbapenemase class assignment was achieved in 97.5% of NDM producers, 54.5% of OXA-48-like producers, and 57.1% of VIM producers. All KPC producers were correctly identified as KPC producers, although carbapenem impermeability was systematically co-reported, preventing single unambiguous assignment. The integrated VITEK2 AES/BIOART solution provides an efficient approach for CPE screening and classification, particularly for NDM and KPC-producers. IMPORTANCE Rapid and reliable detection of carbapenemase-producing Enterobacterales (CPE) is essential for infection control, epidemiological surveillance, and optimized antimicrobial therapy. As the prevalence and diversity of carbapenemases increase, diagnostic tools capable not only of detecting CPE but also predicting carbapenemase classes are increasingly needed to guide treatment decisions. In Europe, the emergence of OXA-48-like variants such as OXA-244 and OXA-484, which exhibit low hydrolytic activity to carbapenems and temocillin, complicates routine phenotypic detection and may lead to diagnostic failure. This study evaluates an automated solution integrating the VITEK2 Advanced Expert System and BIOART expert rules for CPE detection and classification in a representative French epidemiological context. We demonstrate that this integrated approach provides accurate and rapid screening, with good performance for carbapenemase class prediction, particularly for NDM and KPC producers. The implementation of a dedicated rule significantly improves detection of difficult-to-identify OXA-244/OXA-484 producers, addressing an important diagnostic gap.