Diabetic foot ulcers (DFUs) are the most common complications of diabetes resulting from hyperglycemia leading to ischemic hypoxic tissue and nerve damage. Staphylococcus aureus is the most frequently isolated bacteria from DFUs and causes severe necrotic infections leading to amputations with a poor 5-year survival rate. However, very little is known about the mechanisms by which S. aureus dominantly colonizes and causes severe disease in DFUs. Herein, we utilized a pressure wound model in diabetic TALLYHO/JngJ mice to reproduce ischemic hypoxic tissue damage seen in DFUs and demonstrated that anaerobic fermentative growth of S. aureus significantly increased the virulence and the severity of disease by activating two-component regulatory systems leading to expression of virulence factors. Our in vitro studies showed that supplementation of nitrate as a terminal electron acceptor promotes anaerobic respiration and suppresses the expression of S. aureus virulence factors through inactivation of two-component regulatory systems, suggesting potential therapeutic benefits by promoting anaerobic nitrate respiration. Our in vivo studies revealed that dietary supplementation of L-arginine (L-Arg) significantly attenuated the severity of disease caused by S. aureus in the pressure wound model by providing nitrate. Collectively, these findings highlight the importance of anaerobic fermentative growth in S. aureus pathogenesis and the potential of dietary L-Arg supplementation as a therapeutic to prevent severe S. aureus infection in DFUs.IMPORTANCES. aureus is the most common cause of infection in DFUs, often resulting in lower-extremity amputation with a distressingly poor 5-year survival rate. Treatment for S. aureus infections has largely remained unchanged for decades and involves tissue debridement with antibiotic therapy. With high levels of conservative treatment failure, recurrence of ulcers, and antibiotic resistance, a new approach is necessary to prevent lower-extremity amputations. Nutritional aspects of DFU treatment have largely been overlooked as there has been contradictory clinical trial evidence, but very few in vitro and in vivo modelings of nutritional treatment studies have been performed. Here we demonstrate that dietary supplementation of L-Arg in a diabetic mouse model significantly reduced duration and severity of disease caused by S. aureus. These findings suggest that L-Arg supplementation could be useful as a potential preventive measure against severe S. aureus infections in DFUs.
Keywords: L-arginine; Staphylococcus aureus; diabetic foot ulcers; hypoxia; virulence.