Acinetobacter baumannii: emergence of four strains with novel bla(OXA-51-like) genes in patients with diabetes mellitus

Diabetic patients are 10 times more likely to develop Acinetobacter baumannii infections than the rest of the population. Carbapenems are considered one of the very few antibiotics left to treat infections caused by this organism. The aim of this work was to characterise A. baumannii strains isolated from diabetic patients and to investigate whether there is a relationship between certain strains and low-level-carbapenem resistance. Methods: Clinical samples were collected from diabetic patients in hospitals throughout Saudi Arabia from December 2006 to April 2007. API 20 NE, polymorphisms in the 16S-23S-rRNA intergenic region and the presence of a bla OXA-51-like gene were all used for identification. Susceptibility to antimicrobials was determined using agar dilution and disk diffusion methods. Pulsed-field gel electrophoresis (PFGE) coupled with sequence analysis of the bla OXA-51-like genes were used for strain characterization. Polymerase chain reaction (PCR) and multiplex PCR were used to screen for the presence and location of ISAba1 elements and bla OXA-23-like bla OXA-40-like, and bla OXA-58- like genes respectively. Results: twenty isolates were identified as A. baumannii and were all highly resistant to 38% of the antibiotics tested and the majority of isolates were also resistant to 50% of the remaining antibiotics. four strains had low-level meropenem resistance (MIC 4 – 8 mg/L). All isolates were sensitive to imipenem and colistin. Nine strains possessed four novel bla OXA-51-like genes encoding β-lactamases designated OXA-90, OXA-130, OXA-131 and OXA-132, and four strains contained bla OXA-131 with ISAba1 upstream of the gene structure. PFGE showed five separate clusters of OXA-51-like enzymes and the dissemination of strains carrying the four novel enzymes was clonal. This study showed that new strains of A. baumannii characterised by their new bla OXA-51-like gene have emerged. No genes encoding OXA-23-like, OXA-40-like, or OXA-58-like β-lactamases were found. Surveillance of A. baumannii harbouring the bla OXA-131-like gene may be an essential step in monitoring their carbapenem resistance phenotype and may assist in preventing their spread in diabetics.