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Abstract
AcrS is known to be a repressor of efflux pump complexes, but its role in the regulation of acr D is unknown. AcrD is an aminoglycoside efflux pump, closely related to other drug efflux pumps as part of the resistance-nodulationdivision (RND) family in Escherichia coli. The RND family is known to be regulated in a co-ordinated manner, so the role AcrS plays in the regulation of acr D was investigated. AcrD has been shown to be responsible for inducing adaptive resistance to kanamycin following pretreatment with kanamycin at sub-inhibitory levels. The Δ acr S E. coli and wild-type E. coli BW25113 were pretreated with sub-inhibitory concentrations of kanamycin, and then changes in kanamycin resistance and acr D expression were compared. acr D amplified cDNA gene transcripts from Δ acr S and wild-type showed that only wild-type E. coli pretreated with sub-inhibitory kanamycin expressed acr D. However, the kanamycin resistance assays showed that Δ acr S strain has a higher resistance to kanamycin than the wild-type strain after pretreatment. These results suggest that AcrS is a putative activator of acr D, and that the deletion of acr S could possibly lead to aminoglycoside export by other overexpressed RND efflux pumps.