Metabolic reprogramming promotes Staphylococcus aureus serum resistance

Staphylococcus aureus is a leading cause of bloodstream infections causing an estimated 300,000 deaths worldwide. Using a functional genomics approach, our group previously identified that adaptation of S. aureus to human serum is polygenic, with a clinically occurring non-synonymous mutation (V76I) in dihydrolipoamide dehydrogenase (lpdA1/pdhD) improving bacterial survival. In this work, we establish that improved serum survival of strains expressing PdhD V76I is underpinned by enhanced resistance to host-derived antimicrobials, including antimicrobial peptides and host-defence fatty acids which are prevalent in the bloodstream. Here, we demonstrate that the PdhD V76I variant has enhanced diaphorase activity, with both clinical and laboratory strains expressing this variant recycling NADH to NAD⁺ without using respiration, leading to a decrease in membrane potential. Expression of PdhD V76I conferred increased resistance to gentamicin, hydrogen peroxide, LL37, HNP-1 and arachidonic acid. However, strains which utilize PdhD V76I do not display growth defects typical of persisters and small colony variants (SCVs), with decreased NADH accumulation in serum leading to enhanced glycolysis/TCA cycle activity, improving bacterial replication in human serum. Whilst establishment of SCV and persister populations is a key survival strategy in the bloodstream, this work demonstrates how intermediate phenotypes can also be effective at promoting survival in this hostile environment. This highlights the heterogenous nature of S. aureus adaptation to the host environment, with an improved fundamental understanding of these processes required to allow for the development of novel therapeutics which target this process of host adaptation.