Nucleotide sequence of the bla(RTG-2) (CARB-5) gene and phylogeny of a newgroup of carbenicillinases

We determined the nucleotide sequence of the bla gene for the Acinetobacter calcoaceticus beta-lactamase previously described as CARB-5. Alignment of the deduced amino acid sequence with those of known beta-lactamases reveale d that CARB-5 possesses an RTG triad in box VII, as described for the Prote us mirabilis GN79 enzyme, instead of the RSG consensus characteristic of th e other carbenicillinases. Phylogenetic studies showed that these RTG enzym es constitute a new, separate group, possibly ancestors of the carbenicilli nase family.