Probiotic Exopolysaccharide Protects against Systemic Staphylococcus aureus Infection, Inducing Dual-Functioning...

Area of Science:

• Immunology
• Microbiology
• Biochemistry

Background:

• Staphylococcus aureus infections lead to high mortality.
• Exopolysaccharide (EPS) from Bacillus subtilis induces anti-inflammatory M2 macrophages.
• EPS has previously shown protective effects against Citrobacter rodentium-induced colitis.

Purpose of the Study:

• To determine if Bacillus subtilis EPS can protect against systemic Staphylococcus aureus infection.
• To investigate the immunomodulatory effects of EPS on macrophages and host response.

Main Methods:

• Mice were treated with EPS and subsequently infected with Staphylococcus aureus.
• Survival rates, weight loss, systemic inflammation, and bacterial burden were assessed.
• Macrophage phenotypes, intracellular bacterial growth restriction via reactive oxygen species (ROS), T cell activation, and systemic cytokine induction were analyzed.

Main Results:

• EPS treatment significantly enhanced survival and reduced weight loss, inflammation, and bacterial burden in mice infected with S. aureus.
• EPS-induced macrophages exhibited an M2 phenotype but also restricted intracellular S. aureus growth via ROS.
• EPS-induced macrophages limited T cell activation by S. aureus superantigens and abrogated systemic interferon-gamma induction.

Conclusions:

• Bacillus subtilis EPS acts as an immunomodulatory agent.
• EPS induces hybrid macrophages with dual functions: enhancing antibacterial immunity and limiting inflammation.
• This dual action reduces disease severity and promotes host survival during S. aureus infection.