No abstract

Class I integrons were detected in 40.8% (40/98) of Pseudomonas aeruginosa strains and 52.8% (56/106) of Acinetobacter baumannii strains in the Nanjing area of China, including several cassette arrays not previously reported.The rapid dissemination of antibiotic resistance genes among bacterial isolates is an increasing problem in infectious disease. Recent studies have shown that a conserved DNA sequence, integron, may be carried on these episomal genetic structures (12,14). Integrons possess two conserved segments separated by a variable region that includes integrated cassettes, which often include antibiotic resistance genes (11). Many resistance genes are present as gene cassettes within integrons, which may themselves be located on transmissible plasmids and transposons (11). In China, resistance to various antibiotics is common in clinical isolates, often more so than in Western countries, especially among Pseudomonas aeruginosa and Acinetobacter baumannii isolates (7,8,16). However, the frequencies, characteristics, and roles of integrons and gene cassettes in the two species have not yet been investigated in a large-scale study.In order to study the roles of gene cassettes in the two species, we obtained 98 P. aeruginosa isolates and 106 Acinetobacter sp. isolates from four general hospitals in the Nanjing area of China during June 2003 and June 2005. The strains were randomly obtained from a variety of clinical specimens from diverse units of the four hospitals. All bacterial strains were identified by the analytical profile index procedure (API-20NE system; bioMerieux, France). Susceptibility to antimicrobial agents was tested by the disk diffusion method on Mueller-Hinton agar plates, according to Clinical and Laboratory Standards Institute guidelines (2). DNA used for PCR was prepared as described previously (9). All isolates were screened for integrons by PCR using degenerate primers hep35 (5Ј TGCGGGTYAARGATBTKGATTT 3Ј) and hep36 (5Ј CARCACATGCGTRTARAT 3Ј) and HinfI restriction analysis of the integrase gene product (18). Class I integron