In vitro analysis of ISEcp1B-mediated mobilization of naturally occurring beta-lactamase gene blaCTX-M of Kluyvera ascorbata.

ISEcp1B has been reported to be associated with and to mobilize the emerging expanded-spectrum beta-lactamase blaCTX-M genes in Enterobacteriaceae. Thus, the ability of this insertion sequence to mobilize the blaCTX-M-2 gene was tested from its progenitor, Kluyvera ascorbata. Insertions of ISEcp1B upstream of the blaCTX-M-2 gene in K. ascorbata reference strain CIP7953 were first selected with cefotaxime (0.5 and 2 microg/ml). In those cases, ISEcp1B brought promoter sequences enhancing blaCTX-M-2 expression in K. ascorbata. Then, ISEcp1B-mediated mobilization of the blaCTX-M-2 gene from K. ascorbata to Escherichia coli J53 was attempted. The transposition frequency of ISEcp1B-blaCTX-M-2 occurred at (6.4+/-0.5)x10(-7) in E. coli. Cefotaxime, ceftazidime, and piperacillin enhanced transposition, whereas amoxicillin, cefuroxime, and nalidixic acid did not. Transposition was also enhanced when studied at 40 degrees C.