Characterization of molecular mechanisms of resistance to antimicrobial fatty acids in the staphylococci

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Background***Approximately 25% of humans are persistently colonized by S. aureus. Preferred sites of colonization of humans are the anterior nares, axillae, perineum, hands, chest and limbs, while in cattle it is the teat skin. Accordingly, its ability to persist on skin is an important mediator of transmission in both humans and animals. Yet, to persist on skin, S. aureus must resist innate defense barriers of the skin including long-chain unsaturated free fatty acids (uFFAs) which possess antimicrobial activity. uFFAs such as sapienic acid, palmitoleic acid, linoleic acid and arachidonic acid inhibit the growth of S. aureus. Indeed, these microbicidal fatty acids are part of the first line of defense against colonization by microbes. Sapienic acid is released from triglycerides secreted by the sebaceous glands in the skin and its secretion is defective in individuals with atopic dermatitis, resulting in increased carriage of S. aureus and increased susceptibility to infection by S. aureus. Nasal secretions also contain linoleic, arachidonic and palmitoleic acids, while staphylococcal abscesses contain abundant quantities of linoleic acid. S. aureus is an effective colonizer of the skin and nose, despite exposure to antimicrobial fatty acids******Hypotheses***We hypothesize that S. aureus has evolved, or can evolve, mechanisms of resistance to microbicidal fatty acids. We further hypothesize that identification of resistance mechanisms will shed significant insight into the biological targets of uFFAs. ******Progress***My laboratory has identified a heretofore unknown resistance mechanism against uFFAs, involving single nucleotide polymorphisms in RNaseY, a membrane of the RNA degradasome. ******Aims***Elucidating the link between RNaseY SNPs and resistance to fatty acids are the overarching aims of this research program. ***Aim 1: Define the fatty acid resistance mechanism in strains containing RNaseY polymorphisms. Using several parallel lines of investigation, this aim will characterize the RNaseY-dependent mechanism of resistance to fatty acids.***Aim 2: Functional characterization of RNaseY variants. This aim will characterize SNP-associated, gain-of-function changes in known functions of RNaseY. ***Aim 3: Define the link between SNPs and elevated resistance to fatty acids. Amino acid changes in RNaseY will be characterized in detail for their ability to confer increased resistance to fatty acids.***Aim 4: Identification and characterization of S. aureus variants resistant to additional fatty acid structures. This will yield valuable information on fatty acid-structure specific mechanisms of action of fatty acids on the S. aureus cell.******Significance***This discovery-based research program will address important and unique questions concerning physiological responses of S. aureus to microbicidal fatty acids, and the ability of S. aureus to evolve resistance to these compounds.