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

ISEcp1B has been reported to be associated with and to mobilize the emerging expanded-spectrum P-lactamase bla(CTX-M) genes in Enterobacteriaceae. Thus, the ability of this insertion sequence to mobilize the bla(CTX-M-2) gene was tested from its progenitor, Kluyvera ascorbata. Insertions of ISEcp1B upstream of the bla(CTX-M-2) gene in K. ascorbata reference strain CIP7953 were first selected with cefotaxime (0.5 and 2 mu g/ml). In those cases, ISEcp1B brought promoter sequences enhancing bla(CTX-M-2) expression in K. ascorbata. Then, ISEcp1B-mediated mobilization of the bla(CTX-M-2) gene from K. ascorbata to Escherichia coli J53 was attempted. The transposition frequency of ISEcp1B-bla(CTX-M-2) occurred at (6.4 +/- 0.5) x 10(-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.