Staphylococcus aureus Utilizes Host-Derived Lipoprotein Particles as Sources of Fatty Acids

Abstract

Methicillin-resistant (MRSA) is a threat to global health. Consequently, much effort has focused on the development of new antimicrobials that target novel aspects of physiology. Fatty acids are required to maintain cell viability, and bacteria synthesize fatty acids using the type II fatty acid synthesis pathway (FASII). FASII is significantly different from human fatty acid synthesis, underscoring the therapeutic potential of inhibiting this pathway. However, many Gram-positive pathogens incorporate exogenous fatty acids, bypassing FASII inhibition and leaving the clinical potential of FASII inhibitors uncertain. Importantly, the source(s) of fatty acids available to pathogens within the host environment remains unclear. Fatty acids are transported throughout the body by lipoprotein particles in the form of triglycerides and esterified cholesterol. Thus, lipoproteins, such as low-density lipoprotein (LDL) represent a potentially rich source of exogenous fatty acids for during infection. We sought to test the ability of LDLs to serve as a fatty acid source for and show that cells cultured in the presence of human LDLs demonstrate increased tolerance to the FASII inhibitor, triclosan. Using mass spectrometry, we observed that host-derived fatty acids present in the LDLs are incorporated into the staphylococcal membrane and that tolerance to triclosan is facilitated by the fatty acid kinase A, FakA, and Geh, a triacylglycerol lipase. Finally, we demonstrate that human LDLs support the growth of fatty acid auxotrophs. Together, these results suggest that human lipoprotein particles are a viable source of exogenous fatty acids for during infection. Inhibition of bacterial fatty acid synthesis is a promising approach to combating infections caused by and other human pathogens. However, incorporates exogenous fatty acids into its phospholipid bilayer. Therefore, the clinical utility of targeting bacterial fatty acid synthesis is debated. Moreover, the fatty acid reservoir(s) exploited by are not well understood. Human low-density lipoprotein particles represent a particularly abundant source of fatty acids and are present in tissues colonizes. Herein, we establish that is capable of utilizing the fatty acids present in low-density lipoproteins to bypass both chemical and genetic inhibition of fatty acid synthesis. These findings imply that targets LDLs as a source of fatty acids during pathogenesis.

Lipidomic and Ultrastructural Characterization of Cell Envelope ofStaphylococcus aureusGrown in the Presence of Human Serum

“…We have previously shown that SCUFAs became about 25% of the total fatty acid profile of S. aureus grown in 100% total bovine serum (6). Delekta et al grew S. aureus in the presence of human LDL and analyzed the PG species produced under these conditions by mass spectrometry (13). PG species containing C16:1, C18:1, C18:2, and C20:1 were observed.…”

“…It is generally considered that S. aureus is unable to biosynthesize SCUFAs, and cells grown in the presence of serum (6), liver extract (12), and human low-density lipoprotein (LDL) and egg yolk LDL (13) have been shown to contain significant amounts of SCUFAs in their fatty acid profiles. In addition, free fatty acids are incorporated into phospholipids from medium supplemented with them (14, 15).…”

“…In addition, free fatty acids are incorporated into phospholipids from medium supplemented with them (14, 15). Mass spectrometry (MS) analysis suggests that PG 33:1 is a major phospholipid when S. aureus is grown in the presence of LDL, which is likely made up of C18:1 Δ9 (oleic acid) at position sn- 1 and anteiso C15:0 at position sn- 2 based on MS fragmentation (13, 15). The major source of lipids in human serum is from LDL particles that contain cholesterol esters, unesterified cholesterol, triglycerides, and phospholipids (16) (Fig.…”

“…1). S. aureus secretes at least two lipases, S. aureus lipase 1 (Sal1) and glycerol ester hydrolase (Geh) (17-19), that release fatty acids from lipids found in serum (6), and LDL (13). These free fatty acids are then incorporated into S. aureus phospholipids and glycolipids through the FakA/B and PlsXY systems (15, 20), with or without further elongation via the type II fatty acid synthesis (FASII) system (Fig.…”

A FASII inhibitor prevents staphylococcal evasion of daptomycin by inhibiting phospholipid decoy production

“…However, despite excellent in vitro activity, the therapeutic value of inhibitors of fatty acid synthesis as mono-therapeutic agents has attracted much debate [20,21]. Several bacteria, including S. aureus , can utilise fatty acids present in the host to generate phospholipids [21-24]. Although wild-type S. aureus strains cannot fully substitute exogenous fatty acids for endogenous fatty acids synthesised via FASII, there is evidence that some clinical isolates have acquired mutations that enable them to fully bypass endogenous fatty acid biosynthesis by utilising host-derived fatty acids [22,25,26].…”