Adjuvant commensal therapy enhances antibiotic efficacy against Staphylococcus aureus

Staphylococcus aureus is a common human pathobiont whose nasal colonization represents a major risk factor for subsequent infection. The prevalence of antimicrobial resistance, coupled with antibiotic-induced microbiota perturbation, has rendered S. aureus-associated infections increasingly difficult to treat. Commensal bacteria have emerged as potential modulators of both host immune responses and pathogen pathogenesis; however, whether they can act as therapeutic adjuvants to enhance treatment outcomes in S. aureus-associated infections remains unclear. Here, we assess the efficacy of commensal bacteria as an adjuvant therapeutic strategy.

Using A549 Dual™ reporter cells, we demonstrate that commensals and pathobionts elicit distinct activation profiles of NF-κB and interferon regulatory factor (IRF) signaling pathways and differential IL-8 production. In a 3D humanized airway tissue model, D. pigrum significantly enhanced antibiotic-mediated reduction of S. aureus survival relative to antibiotic treatment alone (D. pigrum KPL1914: 37.3% reduction, 95% CI 2.0-72.6%, P_adj = 0.0340; D. pigrum AMBR11: 48.1% reduction, 95% CI 2.3-93.9%, P_adj = 0.0356), while preserving barrier integrity and augmenting pro-inflammatory cytokine responses. However, the loss of efficacy with heat-killed D. pigrum indicates that viable bacteria and active host- and/or pathobiont-directed interactions are required to mediate its anti-S. aureus effects. Dual RNA-seq transcriptomic analysis revealed enrichment of host inflammatory pathways and reduction of S. aureus pathogenic potential during D. pigrum antibiotic adjuvant treatment in the airway tissue model. Furthermore, co-culture experiments revealed that D. pigrum constrains core metabolic pathways in S. aureus.

These findings demonstrate that D. pigrum limits S. aureus through both host immune modulation and direct suppression of bacterial pathogenesis and adaptive fitness, supporting its potential as a microbiota-based therapeutic adjuvant to enhance antibiotic efficacy against S. aureus-associated infections. Video Abstract.