Integrase-Mediated Recombination of the Gene Cassette Encoding the Extended-Spectrum β-Lactamase BEL-1.

Integrons are genetic elements that can acquire and rearrange gene cassettes. The gene encodes an extended-spectrum β-lactamase, BEL-1, that is present at the second position of the variable region of class 1 integrons identified in The mobility of the gene cassette was analyzed under physiological conditions and with the integrase gene being overexpressed. Cassette mobility in was detected by excision/integration into the recipient integron In on the conjugative plasmid R388 with the overproduced integrase. Despite several antibiotic pressures, the cassette remained at the second position in the integron, highlighting its stability in Overexpression of the integrase gene in induced cassette recombination. However, cassettes containing two genes ( and or and ) were excised, suggesting that the cassette site was defective. We show that is a stable gene cassette under physiological growth conditions, irrespective of the selective antibiotic pressure, that may be mobilized upon overexpression of the integrase gene.