Persistence of Multiple Antibiotic Resistant Strains of Acinetobacter baumannii Carrying Class 1 Integron in a Hospital Setting

Forty-nine strains of multiresistant Aceinetobacter baumannii isolated from intensive care unit patients in Royal Brisbane and Women Hospital (RBWH) between 2001 and 2003 and four epidemiologically unrelated strains from three other hospitals were tested (n = 53) for their genetic relatedness using pulsed-field gel electrophoresis (PFGE) and for the presence of different classes of integrons. With PFGE, these strains were divided into three common (C) but closely related types (i.e., C1, C1a, and C1b) and eight single (S) types (S1-S8). C1 contained 40 isolates, while C1a and C1b contained 5 and 2 isolates, respectively. All isolates from Royal Brisbane and Women Hospital (RBWH) were resistant to 12 or more antibiotics. Four common pattern of antibiotic resistance (PAR) was observed among the isolates. The dominant PAR contained 39 strains from RBWH, isolated during 2000 (n = 6), 2001 (n = 16), and 2002 (n = 17) and were resistant to 14 antibiotics. Of these, 36 strains (92%) had identical PAR/PFGE types. Class 1 integrase genes were detected in all of the 53 isolates with 5 isolates also having class 2 integrase gene. No class 3 integrase gene was detected among the isolates. Our data suggest the presence of a dominant and persistent clone of multiresistant A. baumannii strain carrying class 1 integron in this hospital setting.