Strain-specific qPCR assay to track the vaginal colonization of the probiotic Lacticaseibacillus rhamnosus TOM 22.8 strain orally administered

Background: Over the past decade, research on the female reproductive tract microbiota has grown significantly and the use of probiotics has gained growing interest in restoring vaginal microbial balance. In this context, probiotic lactobacilli, topically or orally administered, emerged as a valuable alternative or a complementary approach to conventional antimicrobial therapies. Although topical application allows for a fast and direct action on the altered vaginal ecosystem, the oral intake provides long-term benefits due to the passage through the gastrointestinal tract. Methods: In the present study, in silico analyses were conducted to design a specific primer pair, which was validated by qPCR analysis and used to detect the orally administered Lacticaseibacillus rhamnosus TOM 22.8 probiotic strain in vaginal swabs of women with vaginal dysbiosis. Results: Data showed that qPCR confirmed the specificity of the strain-specific primer pair designed, and no amplification results were seen from 30 Lacticaseibacillus rhamnosus, Lacticaseibacillus casei, and Lacticaseibacillus paracasei strains used for comparison. In addition, the qPCR methodology allowed the detection of the Lacticaseibacillus rhamnosus TOM 22.8 probiotic strain in vaginal swab samples, with cell densities ranging from 5.24 log CFU/mL to 6.65 log CFU/mL. Conclusion: The approach used in the present study revealed the ability of the Lacticaseibacillus rhamnosus TOM 22.8 probiotic strain to survive during the GI tract passage and translocate into the vaginal ecosystem.