Sub-Inhibitory Concentrations of Kanamycin May Induce Expression of the Aminoglycoside Efflux Pump acrD Through the Two-Component Systems CpxAR and BaeSR in Escherichia coli K-12

Abstract

The AcrAD-TolC multidrug efflux complex of Escherichia coli K-12 mediates efflux of aminoglycoside antibiotics. Previous studies have shown that pretreatment of E. coli K-12 with sub-inhibitory concentrations of kanamycin induces adaptive resistance to aminoglycoside antibiotics and that acr D expression is upregulated in the presence of kanamycin through a process that involves two-component systems CpxAR and BaeSR. The exact interactions between the components of the systems are still largely unknown. In this study, the interactions between the various components and their role in transient adaptive resistance against kanamycin was further investigated. E. coli K-12 Δ acr D, Δ bae S, Δ bae R, Δ cpx A, and Δ cpx R single-deletion mutants were examined in order to elucidate the mechanism of acr D regulation. A transient adaptive resistant assay of the E.coli K-12 mutant strains using kanamycin was performed in conjunction with measurements of acr D expression levels using quantitative reverse transcriptase PCR (qRT-PCR) in order to determine the role of each component in the regulation of acr D expression. Our results provide support for a model where acr D transcription and adaptive resistance to kanamycin decrease in the Δ bae S and Δ bae R strains, suggesting a role for these genes as positive regulators of acr D. Also, an increase of acr D level was observed in the Δ cpx A strain, suggesting a negative regulatory role for this sensor. Wild type, Δ cpx A, and Δ cpx R strains displayed similar levels of adaptive resistance to kanamycin, indicating that BaeSR can function independent of CpxAR.