Comparative Characterization of the Cephamycinasebla CMY-1 Gene and Its Relationship with Other b-Lactamase Genes

Aplasmidic b-lactamasewhichhydrolyzescephamycinswasfirstdetectedandreportedin1989.Atthattime itsdescriptionwasrestrictedtophenotypiccharacteristics.Weanalyzedthenucleotidesequenceofitsgeneand exploreditsgeneticrelationshipwithotherblagenes.ThededucedaminoacidsequenceoftheblaCMY-1product was compared with those of other known plasmidic cephamycinases and of chromosomal AmpC b-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 ofP. aeruginosa; CMY-2, BIL-1, and LAT-1 with AmpC ofCitrobacter freundii; and MIR-1 with AmpC of Enterobacter cloacae. Plasmidic cephamycinases are now recognized as clinically relevant class C b-lactamases. blagenesencoding b-lactamaseswhichslowlyhydrolyze7-amethoxy-cephalosporins, e.g., cefoxitin, are generally localized on the bacterial chromosome. Many have been classified as class C b-lactamases (1, 16). However, in 1989 a cephamycinase encoded by a plasmidic gene was found (2). At that time the characterization of the enzyme was restricted mainly to its phenotype, e.g., antibiotic resistance profile and isoelectric point. The comparison of its characteristics with known b-lactamasesresultedinpostulationofthefirstplasmidicexpandedspectrum b-lactamase, including resistance to cephamycins (cephamycinase CMY-1). In this study we confirmed the phenotypic definition of CMY-1 by molecular analysis of its gene (blaCMY-1). Furthermore, the positioning of the CMY-1 b-lactamasewithinthegenetic b-lactamaseclassificationsystemand itsrelationshipwithothercephamycinasesdescribedsincethen