Identification and distribution of the clinical isolates of imipenem-resistant Pseudomonas aeruginosa carrying metallo-β-lactamase and/or class 1 integron genes

To investigate the distribution of the genes of two major metallo-beta-lactamases (MBL; i.e., IMP and VIM) and class 1 integrons (intI) in the clinical imipenem-resistant Pseudomonas aeruginosa, a total of 65 isolates, from a university hospital in Sichuan between December 2004 and April 2005 were screened for MBL genes by PCR using primers specific for bla(IMP-1) , bla(VIM) and bla(VIM-2) genes. The MBL-positive isolates were further assessed for class 1 integrons by PCR using specific primers. The nucleotide sequences of several PCR products were also determined. The results revealed that the bla (VIM) gene was found in 81.5% (53/65) of all isolates, bla(VIM-2) gene was found in only 1 isolate and the intI gene was observed in 45.3% (24/53) of bla(VIM)-positive isolates. One isolate carried simultaneously both bla(IMP-1) and intI genes, and to the best of our knowledge this is the first report of such isolate in southwest China. These observations highlight that the genes for VIM beta-lactamase and class 1 integrons were predominantly present among the imipenem-resistant P. aeruginosa tested, confirming the current widespread threat of imipenem-resistant, integron-borne P. aeruginosa.