Screening of OXA-244 producers, a difficult-to-detect and emerging OXA-48 variant?

Background: OXA-244, a single amino acid variant of OXA-48, demonstrates weaker hydrolytic activity towards carbapenems and temocillin compared with OXA-48. Of note, these antimicrobials are present in high concentrations in several carbapenemase-producing Enterobacterales (CPE) screening media. As a result, some screening media fail to grow OXA-244-producing isolates, while the prevalence of OXA-244 producers is constantly increasing in France. Methods: Here, we evaluate the performance of three commercially available CPE screening media [ChromID (R) CARBA SMART (bioMerieux), Brilliance (TM) CRE (Thermo Fisher) and mSuperCARBA (TM) (MAST Diagnostic)] for their ability to detect OXA-244 producers (n = 101). As OXA-244 producers may also express an ESBL, two additional ESBL screening media were tested (Brilliance (TM) ESBL and ChromID (R) BLSE). MICs of temocillin and imipenem were determined by broth microdilution. The clonality of OXA-244-producing Escherichia coli isolates (n = 97) was assessed by MLST. Results: Overall, the sensitivity of the ChromID (R) CARBA SMART, Brilliance (TM) CRE and mSuperCARBA (TM) media were 14% (95% CI = 8.1%-22.5%), 54% (95% CI = 43.3%-63.4%) and 99% (95% CI = 93.8%-100%), respectively, for the detection of OXA-244 producers. Among the 101 OXA-244-producing isolates, 96% were E. coli and 77%-78% grew on ESBL screening media. MLST analysis identified five main STs among OXA-244-producing E. coli isolates: ST38 (n = 37), ST361 (n = 17), ST69 (n = 12), ST167 (n = 11) and ST10 (n = 8). Conclusions: Our results demonstrated that the mSuperCARBA (TM) medium is very efficient in the detection of OXA-244 producers, unlike the ChromID (R) CARBA SMART medium. The high prevalence of ESBLs among OXA-244 producers allowed detection of 77%-78% of themusing ESBL-specific screening media.