Association Between Continuous Consumption of Yogurt Fermented with Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1, Salivary Antimicrobial Proteins, and Tongue-Coating Microbiota: An Observational Human Study

Background/Objectives: Oral microbial homeostasis is crucial for overall health. Nonetheless, the relationship between probiotics and the oral environment remains unclear. This study investigated the association between continuous consumption of yogurt containing Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 (LbR1 yogurt), salivary antimicrobial proteins (AMPs), tongue-coating microbiota, and upper respiratory tract infection (URTI) frequency. Methods: This observational study was conducted on 53 nursing home care workers, categorized into a group who consumed LbR1 yogurt daily for over 1 year (n = 40, yogurt group) and a non-intake group (n = 13, non-yogurt group). Salivary and tongue-coating samples were collected. Results: The yearly URTI frequency was lower in the yogurt group than in the non-yogurt group (p = 0.003). The salivary β-defensin-2 (HBD2) and β-defensin-3 (HBD3) flow rates were higher in the yogurt group than in the non-yogurt group (p = 0.02 and p = 0.0009, respectively). Fusobacterium nucleatum (F. nucleatum) ssp. animalis abundance was lower in the yogurt group than in the non-yogurt group (p = 0.04). Bayesian network analysis indicated an association between yogurt consumption and the yearly URTI frequency and salivary HBD2 and HBD3 flow rates. Conclusions: Continuous consumption of LbR1 yogurt was associated with elevated salivary HBD2 and HBD3, reduced abundance of F. nucleatum ssp. animalis, and decreased URTI frequency. Thus, LbR1 yogurt intake is associated with modulated oral immunity and microbiota, suggesting a potential link to reduced URTIs. However, as an observational pilot study, its results should be interpreted with caution.