A plasmidic class 1 integron from five Pseudomonas aeruginosa clinical strains harbored aacA4 and nonsense-mutated cmlA1 gene cassettes

Five strains of multidrug-resistant Pseudomonas aeruginosa (P. aeruginosa) were isolated from inpatients at a local hospital in China. The most frequent resistance was to cefoperazone, ciprofloxacin, ceftriaxone, cefotaxime, gentamicin, piperacillin, trimethoprim sulfamethoxazole, and tobramycin. These strains were found to contain the class 1 integron, in which the 2360-bp gene cassettes were flanked by 5′- and 3′-conserved segments. Sequence analysis revealed that the gene cassettes contained aacA4 and cmlA1 genes; however, the latter gene had a nonsense mutation resulting in the production of a truncated protein. To the best of our knowledge, this is the first report of a nonsense mutation in the cmlA1 gene. Moreover, the P. aeruginosa strains showed identical profiles in pulsed-field gel electrophoresis, suggesting that they were derived from the same clone. These results emphasize the importance of controlling the spread of multidrug-resistant pathogens in hospitals.