Evolution of polyamine resistance inStaphylococcus aureusthrough modulation of potassium transport

Abstract

Microbes must adapt to diverse biotic and abiotic factors encountered in host environments. Polyamines are an abundant class of aliphatic molecules that play essential roles in fundamental cellular processes across the tree of life. Surprisingly, the bacterial pathogenStaphylococcus aureusis highly sensitive to polyamines encountered during infection, and acquisition of a polyamine resistance locus has been implicated in spread of the prominent USA300 methicillin-resistantS. aureuslineage. At present, alternative pathways of polyamine resistance in staphylococci are largely unknown. Here we applied experimental evolution to identify novel mechanisms and consequences ofS. aureusadaption when exposed to increasing concentrations of the polyamine spermine. Evolved populations ofS. aureusexhibited striking evidence of parallel adaptation, accumulating independent mutations in the potassium transporter genesktrAandktrD. Mutations in eitherktrAorktrDare sufficient to confer polyamine resistance and function in an additive manner. Moreover, we find that ktr mutations provide increased resistance to multiple classes of unrelated cationic antibiotics, suggesting a common mechanism of resistance. Consistent with this hypothesis, ktr mutants exhibit alterations in cell surface charge indicative of reduced affinity and uptake of cationic molecules. Finally, we observe that laboratory-evolved ktr mutations are also present in diverse naturalS. aureusisolates, suggesting these mutations may contribute to antimicrobial resistance during human infections. Collectively this study identifies a new role for potassium transport inS. aureuspolyamine resistance with consequences for susceptibility to both host-derived and clinically-used antimicrobials.