Integrase-mediated recombination of the bel-1 gene cassette encoding the extended-spectrum {beta}-lactamase BEL-1 [PublishAheadOfPrint]

Integrons are genetic elements that can acquire and rearrange gene cassettes. The bla_BEL-1 gene encodes an extended-spectrum β-lactamase, BEL-1, that is present at second position of the variable region of class 1 integrons identified in Pseudomonas aeruginosa. The mobility of the bel-1 gene cassette was analyzed in physiological conditions and with the integrase gene being overexpressed. Cassette mobility in Escherichia coli was detected by excision/integration into the recipient integron In3 on the conjugative plasmid R388, with the over-produced integrase. Despite several antibiotic pressures, the bel-1 cassette remained at the second position in the integron, highlighting its stability in P. aeruginosa. Overexpression of the integrase gene in E. coli induced the bel-1 cassette recombination. However, cassettes containing two genes (bla_BEL-1/smr2 or bla_BEL-1/aacA4) were excised suggesting that the bel-1 cassette attC site was defective. We showed that bel-1 is a stable gene cassette under physiological growth conditions irrespective of the selective antibiotic pressure, that may be mobilized upon over-overexpression of the integrase gene.

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