Antibacterial activity of a plant natural poly-phenol against zoonotic Streptococcus suis

The increasing emergence and dissemination of multi-drugs resistant bacterial pathogens accelerate the desires for novel antimicrobials. Natural products are great resources for the discovery of antimicrobial compound. In this study, pyrogallol was screened from 25 poly-phenols for its antibacterial activity against multi-drugs resistant Streptococcus suis (S. suis), particularly, pyrogallol had synergistic antimicrobial effect with doxycycline, sulfafurazole and clindamycin, respectively. Pyrogallol showed significant inhibitory effects on bacterial biofilm formation, and caused cell wall and cell membrane injury to S. suis. Furthermore, mechanistic studies demonstrated that pyrogallol might interact with peptidoglycan and decreased the expression of virulence and growth-related genes, such as ftsZ, stK, sly, fbps and luxS. In cell model, pyrogallol protected Nptr cells from S. suis-mediated cell damage. Finally, in mouse model, the pyrogallol and antibiotics combination groups with dosage given in the half could be as effective as antibiotics groups. In summary, these results demonstrated the capacity of pyrogallol serving as a candidate for novel antibiotic alternative and antibiotic adjuvant to circumvent the antibiotics resistance and reduced antibiotic consumption.