Dissemination of blaOXA-58 in Proteus mirabilis isolates from Germany

Abstract

Objectives: Characterization of Proteus mirabilis isolates harbouring blaOXA-58 with emphasis on the genetic environment of this resistance determinant. Methods: Strains of P. mirabilis (n"37) isolated from different patients were tested for the presence of blaOXA-58. The genetic context of blaOXA-58 was determined by WGS of two strains and Sanger sequencing. Clonality of the strains was assessed by PFGE. Susceptibility testing was performed by microdilution according to EUCAST. Results: Four strains isolated in different geographical regions of Germany were positive for blaOXA-58, and WGS showed that this resistance gene was harboured on a plasmid. Sanger sequencing confirmed the presence of two nearly identical plasmids, 6219 and 6208 bp in size, in all four strains. Upstream of blaOXA-58 an ISAba3-like transposase gene was located. The P. mirabilis strains were not clonally related according to PFGE. MICs of meropenemfor three of the strains were only just above the EUCAST breakpoint and the Carba NP test was positive for only two of the strains. Conclusions: To our knowledge, this is the first description of blaOXA-58 in the species P. mirabilis. The resistance gene is harboured by almost identical plasmids in strains not clonally related and from different geographical regions. Apart from an ISAba3-like transposase gene upstream of blaOXA-58 the genetic context is different from blaOXA-58 harboured on plasmids in the genus Acinetobacter. With MICs of meropenem well below the EUCAST breakpoint or only just above it and equivocal or false negative results from the Carba NP test, blaOXA-58 can be easily overlooked in P. mirabilis.