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An outbreak of 95 clinical infections with imipenem-resistant Acinetobacter baumannii in a Chinese hospital was investigated and the carbapenemase-encoding genes and their relationship with ISAba1 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 (17.1 %), cefoperazone/sulbactam (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 blaOXA-66 and blaOXA-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 blaOXA-23 probe hybridized with 200 and 220 kb ApaI chromosomal fragments for type patterns A and B, respectively.

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