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Abstract
Sub-inhibitory levels of kanamycin induce cross-resistance against other classes of antibiotics in Escherichia coli. AcrD, an aminoglycoside transporter in E. coli, is responsible for providing adaptive resistance to kanamycin, however the regulation of AcrD is unknown. As the system of acrB up-regulation must first involve removal of its repressor AcrR, it is possible that AcrR might also have an effect towards AcrD-mediated aminoglycoside resistance. In this study, we explored the possibility that kanamycin-pretreatment of E. coli results in induction of acrD via removal of AcrR repression. The Δ acrR E. coli WOLF-1A was screened alongside a wild-type strain for changes in acrD expression and kanamycin minimal inhibitory concentration (MIC) following pretreatment with sub-MIC levels of kanamycin. MICs were determined using the broth-dilution method, and acrD expression was monitored by gel electrophoresis and analyzed by integrated spot density values of cDNA transcripts, prepared by RT-PCR of extracted RNA. It was found that kanamycin pretreatment increased the kanamycin MIC for wild-type E. coli, but decreased the MIC for E. coli WOLF-1A. Electrophoresis band intensities for acrD were consistent amongst all treatments, suggesting that acrR does not regulate the aminoglycoside transporter acrD.