High prevalence of OXA-51-type class D β-lactamases among ceftazidime-resistant clinical isolates of Acinetobacter spp.: Co-existence with OXA-58 in multiple centres

Abstract

Objectives: This study was designed to demonstrate the prevalence of the newly discovered carbapenem-hydrolysing class D enzymes, OXA-51-type and OXA-58, among clinical isolates of Acinetobacter spp. Methods: A total of 72 isolates from six centres were studied. Isolates were screened by PCR with specific primers for blaOXA-51-type and blaOXA-58. PCR products were sequence-analysed. Plasmids were digested with Eco RV and genomic DNAs were digested with Pvu II. Hybridization experiments were done with digoxigenin-labelled specific probes. Macro-restriction analysis was done on Sma I-digested genomic DNAs. Results: A total of 56 (77.8%) isolates were positive for blaOXA-51-type genes. Sequence analysis of the products from 23 selected isolates revealed the occurrence of multiple alleles in all contributing centres. The blaOXA-58 gene was detected among 10 isolates from five centres. All were also positive for blaOXA-51-type genes. Among the blaOXA-58-positive isolates, two from the same centre were positive for a novel OXA-51 allele (OXA-86). Southern hybridization of plasmids and of genomic DNAs suggested that blaOXA-51-type genes are located on chromosomes whereas bla OXA-58 genes are plasmid borne in these 10 isolates. Plasmid profiles and pulsed-field gel electrophoresis patterns indicated the spread of the blaOXA-58 gene among multiple clones. The blaOXA-51-type and blaOXA-58 co-carrier strains were mostly associated with a pandrug-resistant phenotype. Conclusions: This study indicated that blaOXA-58-bearing plasmids are readily spreading among multiple clones of the blaOXA-51-type-bearing clinical isolates of Acinetobacter spp. Since these isolates are highly resistant to antibiotics this finding indicates the existence of a significant problem in Turkish hospitals. © Copyright 2006 Oxford University Press.