Identification of the naturally occurring genes encoding carbapenem-hydrolysing oxacillinases from Acinetobacter...

Carbapenem resistance is increasingly being reported among Acinetobacter species, and results mostly from the expression of acquired carbapenem-hydrolysing oxacillinases (CHDLs). Several Acinetobacter species intrinsically possess chromosomal CHDL genes: Acinetobacter baumannii (bla(OXA-51) ), Acinetobacter radioresistens (bla(OXA-23) ), and Acinetobacter lwoffii (bla(OXA-134) ). We aimed to identify the progenitors of novel CHDL-encoding genes for identification of potential reservoirs. We performed PCR screening using degenerated internal primers designed from a sequence alignment of the known CHDLs (OXA-23, OXA-40, OXA-51, OXA-58, OXA-134, and OXA-143) applied to a collection of 50 Acinetobacter strains belonging to 23 different species. Two strains of Acinetobacter johnsonii, one strain of Acinetobacter calcoaceticus and two strains of Acinetobacter haemolyticus were found to harbour, respectively, the totally novel bla(OXA-211) -like, bla(OXA-213) -like and bla(OXA-214) -like genes. In addition, the complete genomes of those three species available in GenBank, i.e. one A. johnsonii genome, four A. calcoaceticus genomes, and one A. haemolyticus genome, were analysed and found to be positive for the presence of bla(OXA211) -like, bla(OXA-213) -like and bla(OXA-214) -like genes, respectively. The β-lactamases OXA-211, OXA-213 and OXA-214 are diverse, with amino acid identities ranging from 53% to 76%, as compared with the naturally occurring OXA-51-like CHDL from A. baumannii. These β-lactamases showed a peculiar hydrolysis profile, including mostly penicillins and carbapenems. Regarding bla(OXA-23) in A. radioresistens and bla(OXA-134) in A. lwoffii, these genes were not expressed (or expressed at a non-significant level) in their host. Detection of these β-lactamase genes might be used as a useful tool for accurate identification of these Acinetobacter species.