First Report of with Enhanced Meropenem-Hydrolyzing Ability in in China.

PURPOSE

OXA-10-type class D β-lactamases have shown their evolutionary potential of enhancing carbapenem resistance. This study aimed to elucidate the role of OXA-10 variants in clinical isolated multidrug resistant (MDR) and characterize the first appearance of OXA-677 in China.

METHODS

Six -positive strains were screened by PCR from 41 strains, which were resistant to both carbapenems and ceftazidime-avibactam, collected across China in 2018. The minimum inhibitory concentrations (MIC) were determined with the broth microdilution method. The resistance-associated genes and genetic environment were investigated by whole-genome sequencing (WGS). The function and mechanism of OXA-677 β-lactamase were identified by molecular cloning and protein structure modeling.

RESULTS

All the -positive were MDR strains. They also had outer membrane porin defects and produced β-lactam resistance gene fluoroquinolone-resistant gene , aminoglycoside-resistance gene and , fosfomycin-resistance gene , sulfamethoxazole-resistance gene , and chloramphenicol-resistance gene . All variants were located in a Tn1403-related transposon, containing - -, and - gene cassette arrays, respectively. Notably, the producer showed a high MIC level of meropenem (MIC>64 mg/L). Compared to , was found a G-to-T transversion at position 350, leading to a phenylalanine-for-valine substitution in position 117, which is closer to leucine155 in the omega loop of the active site. MIC of meropenem for DH5α with the recombinant plasmid pHSG398 carrying was elevated by 8 times.

CONCLUSION

We speculate that the OXA-10-like enzymes and the decrease of membrane permeability confer carbapenem resistance, and the V117 substitution in OXA-677 might lead to a higher resistance level of meropenem.