Metallo-β-Lactamases in Clinical Pseudomonas Isolates in Taiwan and Identification of VIM-3, a Novel Variant of the VIM-2 Enzyme

Abstract

A total of 209 clinical isolates of Pseudomonas (193 Pseudomonas aeruginosa , 10 P. putida , 4 P. stutzeri , and 2 P. fluorescens isolates) with reduced susceptibilities to imipenem and/or ceftazidime were subjected to PCR assays with primers specific for bla _IMP-1 , bla _IMP-2 , bla _VIM-1 , and bla _VIM-2 and sequence analysis to identify the metallo-β-lactamases (MBLs) prevalent among these organisms in Taiwan; and 21 isolates gave positive results. Five isolates including two P. putida and three P. stutzeri isolates were found to carry bla _IMP-1 , and six isolates including five P. putida and one P. stutzeri isolates harbored bla _VIM-2 . The remaining 10 isolates were P. aeruginosa , and all were found to carry a novel variant of bla _VIM-2 , designated bla _VIM-3 . There are only two nucleotide differences between bla _VIM-2 and bla _VIM-3 , leading to two amino acid alterations. Our findings indicate that VIM-2 and its variant have become the most prevalent metalloenzymes in Pseudomonas in Taiwan. Southern hybridization with the bla _VIM-2 -, bla _VIM-3 -, and bla _IMP-1 -specific probes revealed that only two VIM-2-producing P. putida isolates appeared to carry the MBL gene on plasmids. Pulsed-field gel electrophoresis showed that six VIM-3-producing P. aeruginosa isolates and two IMP-1-producing P. stutzeri isolates were genetically related, suggesting that the spread of these MBL genes in Taiwan could be due to clonal dissemination as well as genetic exchange between different clones.