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"Simplified carbapenem inactivation method (sCIM) as a reliable tool for detecting OXA-48-producing enterobacterales
Ana Collazos-Blanco1, Ana Belén García-Sáez2, Inés-María Marcos-Palomino2
1Department of clinical Microbiology and Parasitology, Hospital Central de la Defensa "Gómez-Ulla" C.S.V.E, Madrid, Spain. acollazosblanco@gmail.com.
Purpose:
Carbapenemase-producing Enterobacterales (CPE), particularly OXA-48-producing Enterobacterales, represent a major diagnostic and therapeutic challenge due to their frequent low-level carbapenem resistance and delayed microbiological detection. Rapid confirmation of carbapenemase production is essential to optimize antimicrobial therapy and infection control measures.
Methods:
This study evaluated the simplified carbapenem inactivation method (sCIM) for detection of OXA-48-producing Enterobacterales. Unlike the conventional mCIM, sCIM eliminates the preliminary carbapenem inactivation incubation step, simplifying the workflow and reducing turnaround time. A total of 150 OXA-48-producing Enterobacterales were analyzed, together with additional VIM-, KPC-producing, and non-carbapenemase-producing isolates collected from clinical specimens at the Hospital Central de la Defensa "Gómez-Ulla" in Spain. Carbapenemase production was confirmed using the Xpert® Carba-R molecular assay.
Results:
The sCIM detected all OXA-48-producing Enterobacterales with 100% sensitivity (95% CI: 97.6-100%) and no indeterminate results, including isolates with low ertapenem MICs. Results were available after 16-18 h of incubation without previous 4-hour carbapenem inactivation step, simplifying laboratory workflow compared with the conventional mCIM.
Conclusions:
The rapid detection of OXA-48-producing Enterobacterales remains a major diagnostic challenge due to their frequently low carbapenem MICs and subtle phenotypic expression. This study demonstrates that sCIM provides a simple, reliable, and highly sensitive method for detecting these isolates, even in cases with borderline susceptibility profiles. Given its low cost and ease of implementation, sCIM represents a valuable tool for routine clinical laboratories, particularly in high-prevalence or resource-limited settings.
