Valinomycin is an neutrally charged ionophore for with high selectivity for K+ ions, over 10,000x favourability of K+ over Na+ \cite{Varma2008}. The expected hypothetical result of addition of valinomycin will be a reduction in ΔΨ over the cytoplasmic membrane. As an ionophore for K+ ions, it allows a route of equilibration for ΔΨ as K+ can now move freely to neutralise charge difference. This in turn will reduce Δp, which will reduce the ability of S. aureus to uptake isoleucine.