Dihydromyricetin as an Antibiofilm and Antibacterial Agent Against Streptococcus agalactiae

Streptococcus agalactiae (Group B Streptococcus) is a leading causative agent of sepsis, pneumonia and meningitis in neonates and is also a major pathogen responsible for bovine mastitis, posing a substantial threat to food safety and public health via the dairy production chain. The ability of S. agalactiae to form biofilms in the host enhances its resistance to conventional antibiotics and host immune defenses, thereby contributing to persistent and chronic infections. This study aimed to evaluate the antibacterial, antibiofilm, and combined antibacterial effects of dihydromyricetin (DMY) against the S. agalactiae strain GBS2 isolated from bovine mastitis. DMY exhibited significant antibacterial activity against GBS2, with a minimum inhibitory concentration and minimum bactericidal concentration of 0.5 mg/mL. Crystal violet staining and confocal laser scanning microscopy analyses demonstrated that DMY effectively inhibited and disrupted biofilm formation, resulting in looser and less dense biofilm structures compared to untreated controls. Furthermore, reverse transcription-quantitative PCR (RT-qPCR) results revealed that DMY modulated the transcript levels of biofilm-associated genes (csrR, srtA, fbsC, cpsE, and luxS). Additionally, DMY markedly potentiated the antibacterial effect of penicillin G, ciprofloxacin, oxacillin, and vancomycin. These findings suggest that DMY could serve as a natural antibiofilm agent for controlling S. agalactiae contamination in the dairy industry, thereby contributing to the prevention of foodborne infections and reducing reliance on conventional antibiotics.