Metabolomics study of the inhibitory effects of tubuloside A on Streptococcus suis biofilm.

Streptococcus suis (S. suis) is an important zoonotic pathogen. Biofilm formation contributes to persistent and chronic infections, increases the difficulty of bacterial eradication, and may pose a threat to public health. Clinically, S. suis infection is mainly treated with antibacterial drugs. However, biofilm-forming S. suis exhibits enhanced drug tolerance, and conventional drugs are often unable to eradicate established biofilms effectively. At present, screening traditional Chinese medicine monomer drugs to interfere with the formation of biofilms has become a promising strategy for controlling S. suis biofilms. In this study, the antibiofilm effect of tubuloside A (TA) on S. suis ATCC700794 and the associated metabolic changes were investigated using untargeted metabolomics. The minimum inhibitory concentration (MIC) of TA against S. suis ATCC700794 was determined by the broth microdilution method. The effects of TA were studied using crystal violet staining. The morphology of TA treated ATCC700794 cells was observed by scanning electron microscopy. Differentially abundant metabolites were screened using metabolomics and bioinformatics analyses. The MIC of TA was 64 µg/mL, whereas 1/2 MIC (32 µg/mL) of TA significantly inhibited biofilm formation without markedly affecting bacterial growth under the tested conditions and reduced biofilm structural formation. After treatment with 1/2 MIC of TA, 65 annotated metabolites met the screening criteria, including 23 upregulated and 42 downregulated metabolites. Bioinformatic analysis showed that the metabolic changes in S. suis ATCC700794 after TA treatment were mainly associated with glycine, serine and threonine metabolism, purine metabolism, cysteine and methionine metabolism, alanine, aspartate and glutamate metabolism, the citrate cycle, arginine and proline metabolism, and pyruvate metabolism. This study provides preliminary metabolomic evidence that TA-mediated inhibition of S. suis biofilm formation is associated with alterations in amino acid metabolism and central carbon metabolism, offering candidate metabolic clues for future mechanistic studies.