Rapid detection of OXA-23-like, OXA-24-like, and OXA-58-like carbapenemases from Acinetobacter species by real-time PCR.

BACKGROUND

Carbapenemase-producing Acinetobacter species, especially A. baumannii, are frequently associated with treatment failures and hospital outbreaks; thus, rapid and reliable detection of specific resistance markers is paramount. The most common carbapenemases found in A. baumannii, namely OXA-23-like, OXA-24-like, and OXA-58-like, belong to the oxacillinase group (class D β-lactamases) which is notoriously difficult to identify phenotypically due to the lack of specific inhibitors.

AIM

To design and validate a multiplex real-time polymerase chain reaction (PCR) assay to detect and differentiate the above three oxacillinases.

METHODS

All available variants of the above three oxacillinase subfamilies were downloaded (as of November 2019) from the Beta-Lactamase DataBase (http://bldb.eu/) aligned with Clustal Omega and oligonucleotides designed using Primer-BLAST. A multiplex real-time PCR assay that included an internal control to discount inhibition was optimized on the Rotor-Gene Q (Qiagen) using the Rotor-Gene Multiplex PCR Kit (Qiagen) and validated using a panel of 122 previously characterized strains carrying a wide range of β-lactamases, often in combination.

FINDINGS

The in-silico approach enabled the design of oligonucleotides in conserved regions of the OXA-24-like and OXA-58-like alignments. Among the 42 described OXA-23-like variants, a single nucleotide polymorphism (SNP) was present in one of the oligonucleotide binding sites of OXA-27, OXA-166, OXA-811, OXA-812, and OXA-816. The assay was 100% sensitive and highly specific. Inhibition was not observed.

CONCLUSION

The assay is easy to perform with results available in about 70 min. It enables unequivocal detection and differentiation of OXA-23-like, OXA-24-like, and OXA-58-like carbapenemases even when more than one is simultaneously present.