Biochemical characterization of OXA-244, an emerging OXA-48 variant with reduced β-lactam hydrolytic activity

OXA-48-producing Enterobacterales have widely disseminated globally with an increasing number of variants identified. Among them, OXA-244 is increasingly reported, despite detection difficulties.

To determine the steady-state kinetic parameters of OXA-244.

The blaOXA-244 gene was amplified, cloned into plasmids p-TOPO and pET41b+, and transformed into Escherichia coli TOP10 for MIC determination and E. coli BL21 DE3 for purification. Steady-state kinetic parameters and IC50s of clavulanic acid, tazobactam and NaCl were determined using purified OXA-244. Molecular modelling was also performed.

A reduction in MICs of temocillin and carbapenems was observed in E. coli expressing OXA-244 as compared with OXA-48. The kinetic parameters revealed a reduced carbapenemase activity of OXA-244 as compared with OXA-48, especially for imipenem, which was 10-fold lower. Similarly, catalytic efficiency (kcat/Km) was reduced by 4-fold and 20-fold for ampicillin and temocillin, respectively. Kinetic parameters for cephalosporins were, however, similar. Molecular modelling studies evidenced the key role of R214 in OXA-48, establishing salt bridges with D159 and with the carboxylate group of the R1 substituent of temocillin. These interactions are not possible with G214 in OXA-244, explaining the reduced affinity of temocillin for this enzyme. The R214G mutation in OXA-244 is also likely to induce changes in the active site's water network that would explain the decrease in the hydrolysis rate of carbapenems.

Our data confirm that the R214G mutation (present in OXA-244) results in reduced carbapenem- and temocillin-hydrolysing activity, confirming the crucial role of residue 214 in the hydrolysis of these substrates by OXA-48-like β-lactamases.