Clinical severity-dependent virulence of Staphylococcus aureus from human diabetic foot ulcers drives impaired wound healing in a diabetic murine model.

INTRODUCTION

Diabetic foot ulcers (DFUs) are serious complications of type 2 diabetes and are frequently infected with Staphylococcus aureus. However, the virulence mechanisms that enable S. aureus to adapt to diabetic conditions and drive disease progression remain unclear.

METHODS

To investigate the relationship between S. aureus virulence and DFU severity, we freshly isolated S. aureus from DFU patients with clinical severities ranging from Grade 2 (mild) and Grade 4 (severe). We evaluated their virulence characteristics using in vitro assays and an in vivo diabetic pressure wound infection model in diabetic TALLYHO/JngJ mice.

RESULTS

S. aureus isolates from Grade 4 DFUs exhibited significantly greater biofilm formation, hemolytic activity, and resistance to oxidative stress compared to Grade 2 isolates. In the in vivo diabetic pressure wound infection model, Grade 4 isolates induced significantly greater tissue necrosis and delayed wound healing, accompanied by sustained expression of pro-inflammatory M1 macrophage-associated genes (NOS2, IL1B, and IFNG). In contrast, Grade 2 isolates caused minimal tissue necrosis and promoted rapid wound healing with expression of anti-inflammatory M2 macrophage-associated genes (ARG1, IL4, and IL10).

DISCUSSION: Collectively, these findings demonstrate that highly virulent S. aureus strains associated with severe DFUs exhibit enhanced virulence traits that promote host colonization and immune responses skewing macrophage polarization toward a sustained pro-inflammatory M1 phenotype, thereby exacerbating tissue damage and impairing wound healing. These virulence characteristics may serve as functional biomarkers to distinguish pathogenic S. aureus from less pathogenic or opportunistic S. aureus strains in DFUs.