Association of IS5 with divergent tandem bla_CMY-2 genes in clinical isolates of Escherichia coli

Objective: To characterize a unique tandem bla _CMY-2 gene arrangement found in two non-identical clinical strains of Escherichia coli. Methods: Both plasmid and chromosomal DNA were evaluated using PFGE, restriction digest analysis, plasmid profiling and Southern hybridization. bla _CMY-2gene expression and gene copy number were evaluated by realtime PCR. Susceptibilities to selected β-lactam antibiotics were determined by agar dilution. Results: A tandem arrangement for bla _CMY-2 was identified in both isolates and was the only arrangement for bla _CMY-2 observed. These isolates had distinct PFGE and plasmid profiles. Each strain exhibited 2-fold higher bla _CMY-2mRNA expression and up to 8-fold lower β-lactam susceptibility compared with a strain with a single copy of bla _CMY-2. Conclusion: This is the first report of IS5 being associated with tandem bla _CMY-2. IS5 has previously been associated with antibiotic resistance through tandem gene amplification. The unique tandem arrangement provides a mechanism for increased bla _CMY-2expression.