Characterization of bla CMY‐10 a novel, plasmid‐encoded AmpC‐type β‐lactamase gene in a clinical isolate of Enterobacter aerogenes

Aims: We report the description of a novel plasmid‐encoded AmpC β ‐lactamase gene ( bla CMY‐10 ) from Enterobacter aerogenes K9911729 that was isolated from a patient suffering from pneumonia in South Korea. Methods and Results: Using antibiotic susceptibility testing, plasmid analysis, transconjugation and Southern blot analysis, the cefoxitin resistance phenotype reflects the presence of a large plasmid [pYMG‐1 (130 kb)] in Ent. aerogenes K9911729. One β ‐lactamase with the pI of 8·0 from transconjugant of Ent. aerogenes K9911729 was identified by isoelectric focusing on a gel. A 1475 bp DNA fragment containing the bla CMY‐10 gene, identified on pYMG‐1 of Ent. aerogenes K9911729, was sequenced and an open reading frame coding for 382 amino acid, CMY‐10, was found. The 37 class C β ‐lactamases were subclassified into 1a to 1j and CMY‐10 into 1a by phylogenetic analysis. A sequence identical to the common regions in In6, In7 and a novel integron from pSAL‐1 was found upstream from bla CMY‐10 gene at nucleotide 1–71. Conclusions: These results clearly show that bla CMY‐10 gene belongs to the group of ampC ‐related bla genes. Homology analysis among AmpC enzymes or ampC genes implied that integration of the chromosomal ampC gene into a large resident plasmid, followed by transconjugation, was involved in the evolution of bla CMY‐10 gene. Significance and Impact of the Study: The first identification of the bla CMY‐10 gene is of concern as chromosomal β ‐lactamases may cause serious therapeutic problems if their genes are translocated onto plasmids.