Celastrol inhibits Streptococcus suis infection through disrupting arginine metabolism pathway

Given the rising prevalence of Streptococcus 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. This study investigated the antibacterial mechanism of celastrol against S. suis and further demonstrated its potential as an adjuvant to conventional antibiotics.

The in vitro and in vivo anti-S. suis efficacy of celastrol was evaluated through time-killing curves, drug resistance, biofilm formation assays, and a mice-infection model. The synergistic efficacy of celastrol and antibiotics against S. suis was evaluated through a 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 a ΔarcA mutant strain, cellular thermal shift assay, and drug affinity responsive target stability assay. Celastrol-disrupted membrane integrity and function of S. suis were employed.

Celastrol exerted potent anti-S. suis efficacy in vitro and in vivo and, in 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 arginine deiminase, the key enzyme catalysing arginine degradation. Meanwhile, celastrol destroyed membrane integrity, induced reactive oxygen species accumulation, caused proton motive force dissipation, impaired ATP production, and inhibited efflux pump activity.

This study demonstrates that celastrol exerts anti-S. suis efficacy by disrupting arginine metabolism and compromising membrane function.