Trained immunity in recurrent Staphylococcus aureus infection promotes bacterial persistence

Bacterial persister cells, a sub-population of dormant phenotypic variants highly tolerant to antibiotics, present a significant challenge for infection control. Investigating the mechanisms of antibiotic persistence is crucial for developing effective treatment strategies. Here, we found a significant association between tolerance frequency and previous infection history in bovine mastitis. Previous S. aureus infection led to S. aureus tolerance to killing by rifampicin in subsequent infection in vivo and in vitro. Actually, the activation of trained immunity contributed to rifampicin persistence of S. aureus in secondary infection, where it reduced the effectiveness of antibiotic treatment and increased disease severity. Mechanically, we found that S. aureus persistence was mediated by the accumulation of fumarate provoked by trained immunity. Combination therapy with metformin and rifampicin promoted eradication of persisters and improved the severity of recurrent S. aureus infection. These findings provide mechanistic insight into the relationship between trained immunity and S. aureus persistence, while providing proof of concept that trained immunity is a therapeutic target in recurrent bacterial infections involving persistent pathogens.Author summary: Skin and soft tissue infections (SSTIs), one of the most common chronic, relapsing, and refractory diseases for human and animals, are potentially involved in pathogen persistent infection. Escherichia coli tolerance frequency in bloodstream infection was associated with past infection, but little is known about how the previous episodes of infection affect bacterial persistency in subsequent challenges. In this study, we determined persister frequency was significantly associated with previous infection history in bovine mastitis. Using a trained immunity model, we uncovered trained immunity promoted S. aureus rifampicin persistency in secondary challenges, which might correlate with fumarate accumulation. We also demonstrated that combination therapy with metformin and rifampicin improved S. aureus clearance and disease severity. These data provide direct evidence that targeting trained immunity might be an effective strategy for recurrent diseases involving persistent pathogens.