New array of aacA4-catB3-dfrA1 gene cassettes and a noncoding cassette from a class-1-integron-positive clinical strain of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic human pathogen that causes nosocomial infections. This bacterium is characterized by inherent resistance to a wide variety of antimicrobials; the inherent resistance is always mediated by antibiotic resistance genes (3, 10). A genetic element, the integron, is potentially a major agent in the dissemination of multidrug resistance among gram-negative bacteria, especially enteric bacteria and Pseudomonas (2, 6). Class 1 integrons are predominant among integrons that carry resistance cassettes (11, 12). The goal of our study was to analyze the gene cassettes and a noncoding cassette in a class-1-integron-positive clinical Pseudomonas aeruginosa strain isolated from a sputum specimen of a respiratory disease patient in Hebei Province, People’s Republic of China. P. aeruginosa strain P11 was screened for antimicrobial susceptibility by using the disk agar dilution method (7). Results of antimicrobial susceptibility testing showed that strain P11 was resistant to several antibiotics, including cefaclor, cefazolin, cefuroxime, chloramphenicol, gentamicin, trimethoprimsulfamethoxazole, tetracycline, and tobramycin. The intI1 gene, an integron-encoded integrase gene, was amplified by primers specific for intI1 (intM1-U [5 -ACGAGCGCAAGGTTTCGGT3 ] and intM1-D [5 -GAAAGGTCTGGTCATACATG-3 ]). The variable region of the integron was determined to be 2,655 bp by PCR with primers specific for the variable region between the 5 conserved sequence (5 -CS) (in-F [5 -GGCATCCAAGCAGCA AGC-3 ]) and the 3 -CS (in-B [5 -AAGCAGACTTGACCTGA T-3 ]) (8). The 3 -CS of the class 1 integron was also specifically amplified by primers (qacE 1-F [5 -ATCGCAATAGTTGGCG AAGT-3 ] and sul1-B [5 -GCAAGGCGGAAACCCGCGCC3 ]) (5), indicating that the 3 -CS of the class 1 integron possessed the qacE 1 and sul1 genes. In order to identify the gene cassettes harbored in this integron, the 2,655-bp amplicon was