Oral colonization of probiotics: one size fits all?

The clinical application of probiotics for oral health is increasing, yet their colonization dynamics remain poorly understood. This study investigated whether administration timing, strain origin, and host-specific factors influence oral persistence. Two Limosilactobacillus reuteri strains (oral vs. non-oral isolate) were evaluated in two in vivo studies. In the first, participants consumed probiotics either during the day or before bedtime; in the second, daily administration continued for 28 days, followed by a 7-day washout. Probiotic abundance was qPCR quantified and oral microbiomes were sequenced. Additionally, a retrospective analysis of periodontitis patients receiving probiotics was performed. Bedtime administration significantly prolonged probiotic detectability compared to daytime intake. Both strains were largely transient, disappearing within days post-administration, though the oral isolate showed enhanced adhesion. Notably, a subset of participants retained the probiotic for up to a week, suggesting interindividual variability and potential biomarkers of colonization. Periodontitis patients who had higher concentrations of probiotics also displayed more improvement in pocket probing depth of deep pockets. These findings highlight the need to consider timing, strain selection, and host factors in probiotic-based oral health interventions.