β-lactam induction of ISEcp1B-mediated mobilization of the naturally occurring blaCTX-M β-lactamase gene of Kluyvera ascorbata

ISEcp1B is an insertion element associated with the emerging expanded-spectrum beta-lactamase bla(CTX-M) genes in Enterobacteriaceae. Because ISEcp1B-bla(CTX-M)positive strains may be identified from humans and animals, the ability of this insertion sequence to mobilize the bla(CTX-M-2) gene was tested from its progenitor Kluyvera ascorbata to study the effects of amoxicillin/clavulanic and cefquinome as enhancers of transposition. These beta-lactam molecules are administered parenterally to treat infected animals. ISEcp1B-mediated mobilization of the bla(CTX-M-2) gene from K. ascorbata to a plasmid location in Escherichia coli J53 was studied. Transposition assays were performed with overnight cultures with amoxicillin/clavulanic acid and cefquinome at concentrations expected to mimic those found in feces after parenteral administration (0.4-0.008 mg L-1 and 0.32-0.064 mg L-1, respectively). Amoxicillin/clavulanic acid and cefquinome did not modify the transposition frequency (1.85 +/- 1.7 x 10(-7)) whereas ceftazidime (0.5 mg L-1), used as a control, did (5.2 +/- 2.7 x 10(-5)). Therefore, it is likely that neither amoxicillin/clavulanic acid nor cefquinome concentrations as found in the gut flora may enhance mobilization of the bla(CTX-M) genes in Enterobacteriaceae.