SPM-1-producing Pseudomonas aeruginosa: analysis of the ancestor relationship using multilocus sequence typing, pulsed-field gel electrophoresis, and automated ribotyping.

In Brazil, the spread of an endemic clone of SPM-1-producing Pseudomonas aeruginosa has been reported. Recently, a higher genomic variety has been observed among the SPM-1-producing P. aeruginosa isolates. The principal aim of this study was to analyze through multilocus sequence typing (MLST) analysis whether the recently isolated SPM-1-producing P. aeruginosa descend or not from a common ancestor. A total of 50 SPM-1-producing P. aeruginosa exhibiting 11 distinct ribotyping genotypes collected from 11 different Brazilian cities were studied. Three IMP-1-producing P. aeruginosa and two non-metallo-beta-lactamase-producing P. aeruginosa isolates were included in the study as controls. For assignment of allelic numbers and subsequent determination of sequence type (ST), the obtained sequences were compared to existing sequences in the MLST database (www.pubmlst.org/paeruginosa). The eBURSTv3 software was used in this study for establishing the evolutionary relationship and phylogenetic analysis. A total of 5 different STs were identified among 55 P. aeruginosa isolates. All of the SPM-1-producing P. aeruginosa presented an identical allelic profile (ST277), except for one strain. The three IMP-1-producing P. aeruginosa strains were classified as belonging to the ST593, whereas the non-metallo-beta-lactamase-producing P. aeruginosa showed two new distinct STs, ST594 and ST595. Our study shows that SPM-1-producing P. aeruginosa isolates as well as the IMP producers evaluated in this study descend from a common ancestor.