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Abstract
Antibiotic resistance is one of the leading causes of death with 2.8 million antibiotic-resistant infections occurring every year with more than 35,000 deaths in the United States. Staphylococcus aureus (S. aureus) is a gram-positive bacteria that causes bacteremia, endocarditis, skin infections, soft tissue infections, bone and joint infections, and hospital-acquired infections. Daptomycin is the last resort antibiotic that is used for treating the infections caused by methicillin-resistant S. aureus (MRSA) but there are reports on the development of daptomycin resistant S. aureus strains. One of the intriguing differences seen in the daptomycin-resistant S. aureus is the changes in membrane phospholipids. FASII (Type II fatty acid synthesis) plays an important role in the synthesis of membrane phospholipids from fatty acid primers by assisting in the uptake of fatty acids from the host during antibiotic-induced stress. Staphylococcus aureus has a mixture of straight-chain saturated and branched-chain fatty acids, with the ratio of these acids being crucial for maintaining membrane fluidity during stress conditions. This study investigates the role of exogenous unsaturated fatty acids in host phospholipid profile changes and daptomycin susceptibilities. Using Liquid chromatography-Ion mobility-mass spectrometry, we characterized the phospholipids of S. aureus, revealing the presence of unsaturated lipids containing oleic acid as a fatty acid component. These changes in phospholipid compositions were correlated with altered daptomycin susceptibilities, as measured by minimum inhibitory concentrations. Furthermore, we evaluated the effect of exogenous unsaturated fatty acids on S. aureus growth when exposed to higher concentrations of daptomycin. Secondly, we utilized external straight-chain saturated fatty acids to examine the differences from unsaturated fatty acids into S. aureus lipid isomers. Fatty acid isotope labeling strategies were employed to demonstrate the incorporation of saturated fatty acids into S. aureus membrane phosphatidylglycerol lipids, which affect membrane fluidity. Lastly, we analyzed differences in membrane lipid compositions in the presence of exogenous fatty acids grown at various temperatures, providing insights into S. aureus foodborne pathologies. Overall, our findings reveal changes in membrane compositions and daptomycin susceptibility in response to exogenous fatty acids.