Typing and characterization of carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex in a Chinese hospital.

This study was designed to investigate the prevalence of carbapenem-resistant Acinetobacter calcoaceticus-baumannii complex (Acb complex) and to type carbapenemases. The relatedness of 45 isolates of carbapenem-resistant Acb complex collected from a clinical setting was analysed by PFGE. The carbapenemases produced by these isolates were typed by IEF, a three-dimensional test, 2-mercaptopropanoic acid inhibition assay, PCR and DNA cloning and sequencing. Results showed that all 45 isolates were resistant to multiple antibiotics including meropenem. The resistance rates to cefoperazone/sulbactam and ampicillin/sulbactam were 2.2 and 6.5%, respectively. About 71.7-78.3% of these isolates were intermediately resistant to cefepime, ceftazidime and cefotaxime. Forty-five isolates were classified into type A (98%) and B (2%) based on their PFGE patterns. Most of type A isolates were from the ICU. Type A was the dominant isolate, including subtypes A1 (22%), A2 (71%), A3 (2%) and A4 (2%). Only one isolate, from the haematology department, belonged to type B. Forty-three isolates (96%) were positive for carbapenemase. One isolate had two bands by IEF, the pIs of which were 6.64 and 7.17. The band with the pI of 6.64 was OXA-23. The other 42 isolates produced two bands with pIs of 6.40 and 7.01 which could not be inhibited by clavulanic acid, cloxacillin or 2-mercaptopropanoic acid. It can be concluded that the prevalent carbapenem-resistant Acb complex isolates from this hospital all had similar beta-lactamase patterns.