The expression of efflux pump gene lde in ciprofloxacin resistant (Cip(R) ) and susceptible strains of Listeria monocytogenes collected from retail food samples was investigated. For two Cip(R) strains, the MICs of ciprofloxacin decreased four- to eightfold in the presence of reserpine; however, no significant alterations were observed with naturally sensitive isolates. Overexpression of the lde gene induced by ciprofloxacin was observed in two resistant isolates. The present findings indicate that expression of lde and the MICs of ciprofloxacin are well correlated with the presence and absence of reserpine, suggesting that Lde might be involved in ciprofloxacin resistance of L. monocytogenes.
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