Comparative characterization of the cephamycinase bla(CMY-1) gene and its relationship with other beta-lactamase genes

A plasmidic beta-lactamase which hydrolyzes cephamycins was first detected and reported in 1989. At that time its description was restricted to phenotypic characteristics. We analyzed the nucleotide sequence of its gene and explored its genetic relationship with other bla genes. The deduced amino acid sequence of the bla(CMY-1) product was compared with those of other known plasmidic cephamycinases and of chromosomal AmpC beta-lactamases. The results indicate that the relationship of CMY-1 is closest to MOX-1 among the plasmidic cephamycinases and to AmpC of Pseudomonas aeruginosa among the chromosomal cephalosporinases. We conclude that the plasmidic cephamycinases described up to now may be classified into three families, as follows: CMY-1, MOX-1, and FOX-1 with AmpC of P. aeruginosa; CMY-2, BIL-1, and LAT-1 with AmpC of Citrobacter freundii; and MIR-1 with AmpC of Enterobacter cloncae. Plasmidic cephamycinases are now recognized as clinically relevant class C beta-lactamases.