Role of Staphylococcus aureus Formate Metabolism during Prosthetic Joint Infection

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Biofilms produced by Staphylococcus aureus are antibiotic-tolerant and cause significant healthcare burdens, particularly in prosthetic joint infections (PJI).
• Granulocytic myeloid-derived suppressor cells (G-MDSCs) are key immune cells in S. aureus PJI, producing IL-10 to foster biofilm persistence by suppressing monocyte and macrophage activity.

Purpose of the Study:

• To investigate the molecular mechanisms by which S. aureus biofilms respond to immune cells, specifically G-MDSCs and macrophages.
• To elucidate the role of formate metabolism in S. aureus biofilm formation and persistence during infection.

Main Methods:

• Coculturing S. aureus biofilms with G-MDSCs or macrophages followed by RNA sequencing.
• Generating and analyzing a S. aureus formate acetyltransferase (pflB) mutant (ΔpflB) in vitro and in a mouse model of PJI.
• Assessing biofilm structure using confocal microscopy and bacterial burden in vivo.
• Evaluating host immune cell infiltration and bacterial killing.

Main Results:

• G-MDSC coculture upregulated fermentative pathways in S. aureus, including pflB, which is essential for formate production.
• The ΔpflB mutant exhibited altered biofilm structure (taller, more diffuse) and reduced bacterial burden in later stages of PJI in mice.
• The ΔpflB mutant showed increased susceptibility to macrophage killing and altered immune cell infiltration (decreased G-MDSCs, increased neutrophils).
• Host-derived formate influenced bacterial survival, as indicated by formate levels in infected tissues.

Conclusions:

• S. aureus formate metabolism, particularly via the pflB gene, is critical for promoting biofilm persistence and virulence in PJI.
• Targeting formate production or metabolism presents a potential therapeutic strategy to combat S. aureus biofilm infections.