Transition of bla OXA-58-like to bla OXA-23-like in Acinetobacter baumannii Clinical Isolates in Southern China: An 8-Year Study

Background

The prevalence of carbapenem-resistant Acinetobacter baumannii in hospitals has been increasing worldwide. This study aims to investigate the carbapenemase genes and the clonal relatedness among A. baumannii clinical isolates in a Chinese hospital.

Methods

Carbapenemase genes and the upstream locations of insertion sequences were detected by polymerase chain reaction (PCR), and the clonal relatedness of isolates was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing.

Results

A total of 231 nonduplicate carbapenemase gene-harboring A. baumannii clinical isolates recovered from Shenzhen People’s Hospital, were investigated between 2002 and 2009. bla_OXA-23-like, bla_OXA-58-like, bla_OXA-40-like, and ISAba1-bla_OXA-51-like were identified in 119, 107, 1, and 4 isolates, respectively. IS1008-ΔISAba3, ISAba3, and ISAba1 were detected upstream of the bla_OXA-58-like gene in 69, 35, and 3 isolates, respectively. All bla_OXA-23-like genes but one had an upstream insertion of ISAba1. bla_OXA-58-like was the most common carbapenemase gene in A.baumannii before 2008, thereafter bla_OXA-23-like became rapidly prevalent and replaced bla_OXA-58-like in 2009. The majority of bla_OXA-58-like-carrying isolates showed lower level of resistance to imipenem and meropenem (minimum inhibitory concentrations (MICs), 1 μg/ml to 16 μg/ml), compared with the majority of bla_OXA-23-like-carrying isolates (MICs, 16 μg/ml to 64 μg/ml for both imipenem and meropenem). All 231 bla_OXA carbapenemase gene-harboring isolates belonged to 14 PFGE types (A–N), and three dominant clones A, J, and H accounted for 43.3%, 42.0%, and 8.2% of the tested isolates, respectively. Clone A (sequence type ST92/ST208) with bla_OXA-58-like was the most prevalent before 2008. Clone H (ST229) with bla_OXA-23-like became striking between 2007 and 2008. Clone J (ST381) with bla_OXA-23-like rapidly spread and replaced clones A and H in 2009.

Conclusion

This study is the first to reveal that the distinct bla_OXA-23-like-carrying A. baumannii ST381 displaced the previously prevalent bla_OXA-58-like-carrying A. baumannii ST92/ST208, resulting in the rapidly increasing resistance to carbapenems in A. baumannii in Shenzhen People’s Hospital in 2009.