Effect of substrate exposure and other growth condition manipulations on norA expression

Multidrug efflux is a resistance mechanism that simultaneously affects susceptibility to many structurally unrelated compounds. The regulation of norA expression, which encodes the Staphylococcus aureus NorA multidrug efflux pump, is not well understood but the MgrA global regulator and the arlRS locus are involved. The expression of genes encoding proteins related to NorA, such as QacA of S. aureus and Bmr of Bacillus subtilis, is affected by pump substrates. In these instances, substrate interacts with regulatory proteins such that pump gene transcription is increased. The goal of this study was to identify if a similar substrate-level effect exists, or an effect of other growth condition manipulations, on the expression of norA.