Inducible Expression of a Resistance-Nodulation-Division-Type Efflux Pump in Staphylococcus aureus Provides Resistance to Linoleic and Arachidonic Acids

Abstract

Although Staphylococcus aureus is exposed to antimicrobial fatty acids on the skin, in nasal secretions, and in abscesses, a specific mechanism of inducible resistance to this important facet of innate immunity has not been identified. Here, we have sequenced the genome of S. aureus USA300 variants selected for their ability to grow at an elevated concentration of linoleic acid. The fatty acid-resistant clone FAR7 had a single nucleotide polymorphism resulting in an H 121 Y substitution in an uncharacterized transcriptional regulator belonging to the AcrR family, which was divergently transcribed from a gene encoding a member of the resistance-nodulation-division superfamily of multidrug efflux pumps. We named these genes farR and farE, for regulator and effector of fatty acid resistance, respectively. Several lines of evidence indicated that FarE promotes efflux of antimicrobial fatty acids and is regulated by FarR. First, expression of farE was strongly induced by arachidonic and linoleic acids in an farRdependent manner. Second, an H 121 Y substitution in FarR resulted in increased expression of farE and was alone sufficient to promote increased resistance of S. aureus to linoleic acid. Third, inactivation of farE resulted in a significant reduction in the inducible resistance of S. aureus to the bactericidal activity of 100 M linoleic acid, increased accumulation of [ 14 C]linoleic acid by growing cells, and severely impaired growth in the presence of nonbactericidal concentrations of linoleic acid. Cumulatively, these findings represent the first description of a specific mechanism of inducible resistance to antimicrobial fatty acids in a Gram-positive pathogen. IMPORTANCEStaphylococcus aureus colonizes approximately 25% of humans and is a leading cause of human infectious morbidity and mortality. To persist on human hosts, S. aureus must have intrinsic defense mechanisms to cope with antimicrobial fatty acids, which comprise an important component of human innate defense mechanisms. We have identified a novel pair of genes, farR and farE, that constitute a dedicated regulator and effector of S. aureus resistance to linoleic and arachidonic acids, which are major fatty acids in human membrane phospholipid. Expression of farE, which encodes an efflux pump, is induced in an farRdependent mechanism, in response to these antimicrobial fatty acids that would be encountered in a tissue abscess. Staphylococcus aureus has a dichotomous relation with human hosts, being able to establish an asymptomatic commensal relationship, but is also historically known as a leading cause of human infectious morbidity and mortality. Significantly, death attributed to S. aureus in the United States is now comparable to mortality rates for AIDS, tuberculosis, and viral hepatitis (1-3). Not surprisingly, therefore, S. aureus has been the subject of intensive research on mechanisms of pathogenesis and acquisition and transfer of antibiotic resistance and of efforts to identify potential vaccine antigens (4-6). Until the late ...

Oleate hydratase from Staphylococcus aureus protects against palmitoleic acid, the major antimicrobial fatty acid produced by mammalian skin

“…The levels of ohyA mRNA were elevated slightly by three fatty acids (18:1(9Z), 16:1(6Z), and 18:2(9Z,12Z)). Although we detected induction of ohyA expression in the presence of these unsaturated fatty acids, the up-regulation of ohyA transcription was not robust compared with the highly regulated farE gene that is controlled by the FarR transcriptional regulator (12,19) (Fig. 5C).…”

“…4). (12,19) and an SaOhyA substrate ( Table 1). Antimicrobial fatty acids act to permeabilize the S. aureus membrane, resulting in the release of intracellular metabolites (like ATP) and low-molecularweight proteins (like ACP) into the medium (12).…”

The Pseudomonas aeruginosa efflux pump MexGHI-OpmD transports a natural phenazine that controls gene expression and biofilm development

“…It would be interesting to test whether AcrZ is involved in resistance to the fatty acids and bile salts among the suggested ecological substrates of AcrB, particularly considering that acrZ is regulated by a transcription factor that is sensitive to these compounds (14,15). Studies elucidating the ecologically relevant or endogenous inducers and substrates of efflux pumps will ultimately help us to better understand their evolution, maintenance in diverse genomes, and critical roles in the physiology of pathogens and malignant host cells (58)(59)(60).…”

Role of the Tet38 Efflux Pump in Staphylococcus aureus Internalization and Survival in Epithelial Cells

“…Examples of such induction phenomena were reported in the expression of the efflux pump genes norA, norB, and tet38 of Staphylococcus aureus in response to low free iron, acidity/low-oxygen conditions, and tetracycline and fatty acids, respectively (5)(6)(7). Recently, the resistance-nodulation-division (RND) family efflux pump FarE of the fatty acid resistance system farR-farE of S. aureus was reported to be induced by linoleic and arachidonic acids (8). The overexpressed FarE efflux pump extrudes and confers resistance to these two fatty acids.…”

“…The overexpressed FarE efflux pump extrudes and confers resistance to these two fatty acids. FarE expression is controlled by the regulator FarR, a member of the AcrR family of regulators (8). Several efflux pumps, such as CmeAB of Campylobacter jejuni and AcrAB of Escherichia coli, have also been shown to have dual functions, conferring resistance to antimicrobial compounds and contributing to the bacterium's ability to invade and survive in host cells or specific host environments (9,10).…”