Detection of OXA-type carbapenemases and integrons among carbapenem-resistant Acinetobactor baumannii in a Teaching Hospital in China

The increasing trend of carbapenem-resistance (CR) and multi-drug resistance (MDR) in A. baumannii worldwide has limited the therapeutic effectiveness of antibiotic therapy. The study was conducted to determine the prevalence of carbapenemases and integrons among the isolates of imipenem-resistant A. baumannii (IRAB). A total of 71 non-repetitive imipenem-resistant A. baumannii isolates were collected and tested for susceptibility to 17 antimicrobials. The modified Hodge test and EDTA-disc synergy test were performed for the screening of carbapenemases and metallo-beta-lactamases (MBLs) production, respectively. Isolates were then subjected to multiplex-PCR targeting genes encoding for OXA-type carbapenemase, MBLs and integrases. Random amplified polymorphic DNA (RAPD) genotyping was performed to assess genetic relatedness. All isolates exhibited multi-drug resistant phenotype. Colistin was the most active antimicrobial agent tested. Seventy-one isolates (100%) demonstrated positive in the modified Hodge test. Thirty-nine isolates showed positive in the EDTA-disc synergy test, however, no MBL genes were detected. All strains possessed a bla(OXA-51)-like gene. The co-existence of bla(OXA-51)-like/bla(OXA-23)-like/intI1, bla(OXA-51)-like/bla(OXA-23)-like, bla(OXA-51)-like/bla(OXA-24)-like was detected in 91.6% (n = 65), 5.6% (n = 4), 2.8% (n = 2), respectively. Analysis of the genetic context of bla(OXA-23) showed the presence of ISAba1 upstream of bla(OXA-23). No ISAba1 was detected upstream of bla(OXA-51). Two different gene cassettes were found in these strains, and a high prevalence of aacA4, aadA1 and catB8 genes was observed. RAPD of 71 isolates showed 7 genotypes. The strains were mainly recovered from patients in intensive care unit, neurosurgery and department of respiratory disease. These findings show that multi-drug resistance in A. baumannii is a common problem. This study also shows a high distribution of bla(OXA-23)-like and intI1 genes in imipenem-resistant A. baumannii isolates. The clonal spread played an important role in the increase of OXA-23 producing IRABs in the hospital environment.