Hidden in plain sight: OXA-244 can be missed by phenotypic screening for carbapenemase-producing Enterobacterales

The prevalence of oxacillinase (OXA)-244-producing Enterobacterales is increasing in Europe, but their detection on screening media is limited. We assessed the proportion of OXA-244 carriage among carbapenemase-producing Enterobacterales (CPE) isolates, and specifically among OXA-48-like producers, at our hospital, addressing the challenges posed by conventional detection methods.

Patients were screened with a rectal swab. For cases with a positive polymerase chain reaction (PCR) for OXA-48 but negative culture on ChromID® CARBA SMART agar, the rectal swab was inoculated on mSuperCARBA® agar, and ChromID® CPS ELITE agar if negative. An additional ChromID® extended-spectrum β-lactamase (ESBL) agar could also be plated and incubated.

All patients with a CPE detection from July 2023 to July 2024 were included in the retrospective analysis. The OXA-244 variant was identified in 16 cases, on the following agar plates: 13 on mSuperCARBA® (also recovered on 5 ChromID® ESBL agar), and 3 on ChromID® CPS ELITE (also recovered on 3 ChromID® ESBL agar). OXA-244 producers represented 21% of all CPE isolates and 28% of OXA-48-like producers. All isolated OXA-244 producers were Escherichia coli.

OXA-244 variant poses diagnostic and surveillance challenges. Its high proportion among CPE isolates, and particularly among OXA-48-like producers, in our study suggests that this variant may be underdetected and highlights the need for adapted screening methods, with PCR prioritized for detecting OXA-244 carriers. Inadequate screening strategies can lead to undetected transmission and increase the risk of outbreaks.