Carbapenemase OXA-423: A Novel OXA-23 Variant in Acinetobacter baumannii

Abstract

Purpose

A novel variant of OXA-23, named OXA-423, was identified in an Acinetobacter baumannii clinical isolate. The aim of this study was to analyse the resistance phenotype of OXA-423.

Methods

The A. baumannii strain WY-0713 was isolated from an intensive care unit patient. PCR was used to detect the bla_OXA-23-like genes. Amplifying, cloning and sequencing were performed for the complete bla_OXA-23-like. The novel bla_OXA-423 and its ancestor bla_OXA-23 were cloned into the expression vector pET-28b(+), and transformed into E. coli Rosetta (DE3) for antibiotic susceptibility testing. SDS-PAGE, modified Hodge test and CarbaNP test were used for detecting the expression of OXA-423 and OXA-23.

Results

PCR screening of A. baumannii WY-0713 was positive for bla_OXA-23-like genes. Sequencing of the PCR product identified a novel bla_OXA-23-like, named bla_OXA-423 which encoding  OXA-423. OXA-423 differed from OXA-23 by a crucial amino acid substitution (Val128Ala). The V128A substitution was located at the conserved active-site motifs SAV of OXA-23. Antibiotic susceptibility testing performed using isogenic E. coli showed that the MICs of E. coli Rosetta (pET-OXA-423) for penicillins and carbapenems were lower (reduced MICs 4-fold to 16-fold) than that of E. coli Rosetta (pET-OXA-23). The MICs of cefotaxime, ceftazidime and aztreonam for both transformants remained the same as the acceptor strain. Moreover, OXA-423 was slightly inhibited by sulbactam, clavulanic acid and tazobactam. SDS-PAGE analysis showed that OXA-423 and OXA-23 were conspicuously expressed. Modified Hodge test and CarbaNP test were positive demonstrated both of them were functional.

Conclusion

OXA-423, the first report of an amino acid substitution located at conserved active-site motifs of OXA-23, conferred lower MIC values of penicillins and carbapenems as compared with OXA-23, while without affecting the resistance profiles of expanded-spectrum cephalosporins and aztreonam.

Keywords:

• OXA-423
• OXA-23
• Acinetobacter baumannii
• carbapenemase
• CHDL

Acknowledgments

Special thanks to George Jacoby for assistance with the numbering of OXA-423. This work was funded by Anhui Province Key Laboratory of Active Biological Macro-molecules Research (LAB201607), and Natural Science Foundation of Anhui Province of China (1808085QC85).

Ethics Statement

The isolation of clinical strain was part of the routine hospital laboratory procedure, without the need for informed consent and ethics committee approval. The study complied with the Declaration of Helsinki.

Disclosure

The authors report no conflicts of interest in this work.