A nosocomial outbreak of Acinetobacter baumannii isolates expressing the carbapenem-hydrolysing oxacillinase OXA-58

Objective: The aim of this study was to analyse the spread of the bla(OXA-58) gene as a source of carbapenem resistance in Acinetobacter baumannii in the burns unit of a university hospital in Toulouse in 2003-2004. Methods: Six carbapenem-resistant A. baumannii isolates from six patients, and a carbapenem-resistant environmental A. baumannii isolate were collected in the burns unit of the Rangueil hospital (Toulouse). Susceptibility tests were carried out by disc diffusion and agar dilution methods. The detection of the bla(OXA-58) gene was conducted by PCR followed by sequence analysis. Plasmids were extracted and hybridized with a probe specific for bla(OXA-58). DNA fingerprints were obtained by pulsed-field gel electrophoresis of ApaI- or SmaI-digested chromosomal DNA of the tested strains. Results: The multidrug-resistant clinical isolates had a similar 30 kb plasmid that encoded the carbapenem-hydrolysing beta-lactamase OXA-58. These isolates were clonally related. The unrelated environmental carbapenem-resistant A. baumannii isolate had a similar bla(OXA-58)-carrying plasmid, suggesting spread of this gene. Conclusions: A novel oxacillinase was the source of carbapenem resistance in the A. baumannii isolates. Its gene was plasmid-, but not integron-borne.