Celastrol inhibits Streptococcus suis infection through disrupting arginine metabolism pathway.

OBJECTIVES: Given the rising prevalence of Streptococcus suis (S. suis) infection and the reduced effectiveness of traditional antibiotics, the development of novel alternative therapeutics or synergistic adjuvants to improve antimicrobial efficacy is urgently required. Celastrol displays antibacterial effects, but the specific mechanism by which celastrol exerts its anti-S. suis activity through interference with arginine metabolism remains unexplored. PURPOSE: This study investigated the antibacterial mechanism of celastrol against S. suis and further demonstrated its potential as an adjuvant to conventional antibiotics. METHODS: The in vitro and in vivo anti-S. suis efficacy of celastrol were evaluated through time-killing curves, drug resistance, biofilm formation assays and mice infection model. The synergistic efficacy of celastrol and antibiotics against S. suis was evaluated through checkerboard microdilution assay. Transcriptomic analysis was performed to analyze the potential anti-S. suis pathways of celastrol. Anti-S. suis target of celastrol was elucidated using ΔarcA mutant strain, CETSA and DARTS assays. Celastrol-disrupted membrane integrity and function of S. suis were employed. RESULTS: Celastrol exerted potent anti-S. suis efficacy in vitro and in vivo, and combination with antibiotics exhibited synergistic antibacterial efficacy. We found that celastrol treatment downregulated arginine-metabolism genes including arcA, argF, and argR. Importantly, celastrol physically interacted with recombinant ADI, the key enzyme catalyzing arginine degradation. Meanwhile, celastrol destroyed membrane integrity, induced ROS accumulation, caused proton motive force (PMF) dissipation, impaired ATP production and inhibited efflux pump activity. CONCLUSION: This study demonstrates that celastrol exerts anti-S. suis efficacy by disrupting arginine metabolism and compromising membrane function.