Detection of co-harboring OXA-58 and NDM-1 carbapenemase producing genes resided on a same plasmid from an Acinetobacter pittii clinical isolate in China

Objectives: Acinetobacter pittii has become an emerging opportunistic noscomial pathogen worldwide with multi-drug resistance. In the present study, an A. pittii strain was isolated from bronchoalveolar lavage fluid sample harboring both OXA-58 and NDM-1carbapenemase producing genes. The mechanisms of carbapenem resistance of the A. pittii strain was investigated.

Materials and methods: Carbapenemase producing genes were examined by PCR and DNA sequencing. S1-PFGE was used to localize carbapenemase encoding genes. Filter mating and electrotransformation were used to investigate the transferability of such carbapenemase encoding genes between different strains. Genetic surroundings of bla _OXA-58 and bla _NDM-1 genes were detected as well.

Results: The A. pittii strain, carrying both OXA-58 and NDM-1 carbapenemase encoding genes, was resistant to all β-lactam antibiotics, while suscepitible to ciprofloxacin, levofloxacin, tobramycin, cotrimoxazole and tigecycline. Southern blot hybridization for the bla _OXA-58 and bla _NDM-1 gene indicated that the two genes locate in the same plasmid with molecular weight of 310.1-336.5kb. Bla _OXA-58 was located in an ISAba3-bla _OXA-58-ISAba3-like structure, and the blaNDM-1 gene cluster was embedded in an ISAba125-aphA6- bla _NDM-1 -ble _MBL -ΔtrpF-dsbC-cutA structure sequentially.

Conclusion: In the present study, it is first reported an A. pittii clincal strain in China, co-harboring OXA-58 and NDM-1 carbapenemase producing genes residing on a same plasmid. In hospital and community settings, it is of great significance and urgence to increase the surveillance of these kinds of organisms.