Stenotrophomonas maltophilia intrinsically produces at least two inducible b-lactamases, L1 and L2. The allelic variation of L1 genes, ranging from 1 to 21%, is known to be prominent in S. maltophilia species. L1 b-lactamase genes of S. maltophilia from 20 clinical isolates were separately cloned and sequenced. Among the 20 isolates, the sequences of L1 genes revealed two different lengths of 870 or 873 bp, respectively. In addition to the twenty L1 sequences obtained in this study, seven L1 full-length sequences from GenBank database were included for phylogenetic analysis. The presence of seven distinct phylogenetic groups, with a cutoff value of 96% identity, was observed, namely, groups L1-1 to L1-7, respectively. Two clusters of L1 genes (group L1-2 and L1-3) are firstly reported.?
