Dissemination of imipenem-resistant Acinetobacter baumannii strains carrying the ISAba1-blaOXA-23 genes in a Chinese hospital

An outbreak of 95 clinical infections with imipenem-resistant Acinetobacter baumannii in a Chinese hospital was investigated and the carbapenemase-encocling genes and their relationship with ISAba 1 of these and a further 16 isolates recovered from the intensive care unit (ICU) environment were analysed. Almost all isolates were resistant to a wide range of antimicrobials; the lowest resistance rates were found for polymyxin E (117.1 %), cefoperazone/sulbactarn (30.6 %) and ampicillin/sulbactam (67.6 %). Six pattern types defined by DNA macrorestriction patterns were distinguished among the clinical isolates with dissemination of pattern A (50 isolates) to patients in seven hospital units and pattern B (35 isolates) to eight units; the environmental isolates from ICUs were also of pattern A. All isolates were positive for the bla(OXA-66) and bla(OXA-23) genes. The OXA-23-encoding gene was located 34 bp downstream of ISAba1. No plasmids were detected and conjugal transfer of resistance was not demonstrated. The bla(OXA-23) probe hybridized with 200 and 220 kb Apal chromosomal fragments for type patterns A and B-1 respectively.