Previous studies demonstrated that sufferers with halitosis can be significantly improved with Lacticaseibacillus paracasei ET-22 (ET-22) postbiotics intervention. The objectives of this investigation were to identify the primary components responsible for inhibiting oral malodor. This study demonstrated that cell-free supernatants (CFSs) were more effective in inhibiting production of volatile sulfur compounds (VSCs). Untargeted metabolomics identified CFSs as primarily consisting of organic acids, lipids, peptides, and nucleotides. Among the potential active components, phenyllactic acid (PLA) and peptide GP(Hyp)GAG significantly inhibited microbial-induced VSCs production, with VSC concentrations reduced by 42.7% and 44.6%, respectively. Given the correlation between biofilms and halitosis, microstructural changes in biofilms were examined. PLA suppressed the biomass of the biofilm by 41.7%, while the biofilm thickness was reduced from 202.3 to 70.0 μm. GP(Hyp)GAG intervention reduced the abundance of Fusobacterium nucleatum and Streptococcus mutans within the biofilm, and the expression of biofilm-forming genes FadA and Gtfb were also suppressed by 41.8% and 59.4%. Additionally, the VSC production capacities were reduced due to the decrease in VSC producing bacteria (F. nucleatum, Prevotella intermedia, and Solobacterium moorei) and down-regulation of Cdl and Mgl genes. Collectively, the current study proved that PLA and GP(Hyp)GAG may be the main contributors to halitosis inhibition by ET-22 postbiotics.
Keywords: Biofilm; Oral malodor; Oral microbiome; Postbiotic; Untargeted metabolomics.