RESUMO
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 pathogen Staphylococcus aureus is highly sensitive to polyamines encountered during infection, and acquisition of a polyamine resistance locus has been implicated in spread of the prominent USA300 methicillin-resistant S. aureus lineage. At present, alternative pathways of polyamine resistance in staphylococci are largely unknown. Here we applied experimental evolution to identify novel mechanisms and consequences of S. aureus adaption when exposed to increasing concentrations of the polyamine spermine. Evolved populations of S. aureus exhibited striking evidence of parallel adaptation, accumulating independent mutations in the potassium transporter genes ktrA and ktrD. Mutations in either ktrA or ktrD are 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 natural S. aureus isolates, suggesting these mutations may contribute to antimicrobial resistance during human infections. Collectively this study identifies a new role for potassium transport in S. aureus polyamine resistance with consequences for susceptibility to both host-derived and clinically-used antimicrobials.
RESUMO
The microbiota can promote host health by inhibiting pathogen colonization, yet how host-resident fungi, or the mycobiota, contribute to this process remains unclear. The human skin mycobiota is uniquely stable compared to other body sites and dominated by yeasts of the genus Malassezia . We observe that colonization of human skin by Malassezia sympodialis significantly reduces subsequent colonization by the prominent bacterial pathogen Staphylococcus aureus . M. sympodialis secreted products possess potent bactericidal activity against S. aureus and are sufficient to impair S. aureus skin colonization. This bactericidal activity requires an acidic environment and is exacerbated by free fatty acids, demonstrating a unique synergy with host-derived epidermal defenses. Leveraging experimental evolution to pinpoint mechanisms of S. aureus adaptation in response to the skin mycobiota, we identified multiple mutations in the stringent response regulator Rel that promote survival against M. sympodialis . Similar Rel alleles have been reported in S. aureus clinical isolates, and natural Rel variants are sufficient for tolerance to M. sympodialis antagonism. Partial stringent response activation underlies tolerance to clinical antibiotics, with both laboratory-evolved and natural Rel variants conferring multidrug tolerance. These findings demonstrate the ability of the mycobiota to mediate pathogen colonization resistance, identify new mechanisms of bacterial adaptation in response to fungal antagonism, and reveal the potential for microbiota-driven evolution to shape pathogen antibiotic susceptibility. Highlights: - M. sympodialis reduces colonization of human skin by S. aureus - Bactericidal activity of M. sympodialis is exacerbated by features of the skin niche - S. aureus Rel variants are sufficient for tolerance to Malassezia antagonism - Evolved tolerance to yeast antagonism coincides with S. aureus multidrug tolerance.