Carbenicillin-hydrolysing penicillinase mediated by a plasmid of Proteus mirabilis and its relationship to the PSE-type enzymes of Pseudomonas aeruginosa

The nucleotide sequence of a carbenicillin-hydrolysing (carbenicillinase) gene occurring in an endogenous plasmid, pCS229, of Proteus mirabilis was determined. The amino acid sequence of the mature enzyme, comprising 271 amino acids with a molecular mass of 29506 Da, was deduced. The pCS229 carbenicillinase showed only 46.4% similarity, in the overall amino acid sequence, to the chromosomal carbenicillinase of Pr. mirabilis GN79; however, the enzyme showed about 98% similarity to a Pseudomonas-specific plasmid-encoded carbenicillinase, PSE-4, that was isolated from Pseudomonas aeruginosa. Only five of 271 amino acids differed from those of PSE-4. This study proved the close relationship between the carbenicillinase genes distributed in Pr. mirabilis and Ps. aeruginosa.