The Use of Acute Immunosuppressive Therapy to Improve Antibiotic Efficacy against Intracellular Staphylococcus aureus

Abstract

Interactions between Staphylococcus aureus and the host immune system can have significant impacts on antibiotic efficacy, suggesting that targeting and modulating the immune response to S. aureus infection may improve antibiotic efficacy and improve infection outcome. As we've previously shown, high levels of reactive oxygen species (ROS), associated with an M1-like proinflammatory macrophage response, potently induce antibiotic tolerance in S. aureus. Although the proinflammatory immune response is critical for initial control of pathogen burden, recent studies demonstrate that modulation of the macrophage response to an anti-inflammatory, or M2-like, response facilitates resolution of established S. aureus skin and soft tissue infections, arthritis, and bacteremia. Here, we evaluated the impact of host-directed immunosuppressive chemotherapeutics and anti-inflammatory agents on antibiotic efficacy against S. aureus. IMPORTANCE Staphylococcus aureus is the leading cause of hospital-acquired infections in the United States with high rates of antibiotic treatment failure. Macrophages represent an important intracellular niche in experimental models of S. aureus bacteremia. Although a proinflammatory macrophage response is critical for controlling infection, previous studies have identified an antagonistic relationship between antibiotic treatment and the proinflammatory macrophage response. Reactive oxygen species, produced by macrophages during respiratory burst, coerce S. aureus into an antibiotic tolerant state, leading to poor treatment outcome. Here, we aimed to determine the potential of host-directed immunomodulators that reduce the production of reactive oxygen species to improve antibiotic efficacy against intracellular S. aureus.

Keywords: Staphylococcus aureus; antibiotics; immunomodulation; persister cells; reactive oxygen species.

FIG 1

Treatment of macrophages with the immunomodulators dexamethasone and rosiglitazone improves antibiotic efficacy against S. aureus. (A) CFU of S. aureus recovered from BMDMs treated with dexamethasone or rosiglitazone, followed by treatment with rifampicin. Black bars, no antibiotic; gray bars, rifampicin. (B) % survival extrapolated from (A). (C) Relative light units (RLU) of L012 (proxy for ROS) in macrophages treated as in (A). Data are representative of n = 3 biological samples. Error bars represent standard deviation. Statistical significance was determined using one-way ANOVA with Sidak’s multiple comparison test. There is no significant difference in S. aureus killing in the absence of rifampicin (compare black bars in A).

FIG 2

Treatment of macrophages with Nrf2 signaling activators improves antibiotic efficacy against S. aureus. (A, D) CFU of S. aureus recovered from BMDMs treated with sulforaphane (A) or CDDOMe ARAPas (D), followed by treatment with rifampicin. (B, E) % survival extrapolated from (A, D respectively). (C, F) Relative light units (RLU) of L012 (proxy for ROS) in macrophages treated as in (A, D respectively). Data are representative of n = 3 biological samples. Error bars represent standard deviation. Statistical significance was determined using Student’s unpaired t test. There is no significant difference in S. aureus killing in the absence of rifampicin (compare black bars in A, D).