Effect of oral consumption of capsules containing Lactobacillus paracasei LPC-S01 on the vaginal microbiota of healthy adult women: a randomized, placebo-controlled, double-blind crossover study

Abstract

Oral consumption of probiotics is practical and can be an effective solution to preserve vaginal eubiosis. Here, we studied the ability of orally administered Lactobacillus paracasei LPC-S01 (DSM 26760) to affect the composition of the vaginal microbiota and colonize the vaginal mucosa in nondiseased adult women. A total of 40 volunteers took oral probiotic (24 billion CFU) or placebo capsules daily for 4 weeks, and after a 4-week washout, they switched to placebo or probiotic capsules according to the crossover design. A total of 23 volunteers completed the study according to the protocol. Before and after capsule ingestion, vaginal swabs were collected for qPCR quantification to detect L. paracasei LPC-S01 and for 16S rRNA gene sequencing. Vaginal swabs were grouped according to their bacterial taxonomic structure into nine community state types (CSTs), four of which were dominated by lactobacilli. Lactobacillus paracasei LPC-S01 was detected in the vagina of two participants. Statistical modeling (including linear mixed-effects model analysis) demonstrated that daily intake of probiotic capsules reduced the relative abundance of Gardnerella spp. Quantitative PCR with Gardnerella vaginalis primers confirmed this result. Considering the pathogenic nature of G. vaginalis, these results suggest a potential positive effect of this probiotic capsule on the vaginal microbial ecosystem.

Keywords: Gardnerella; Lactobacillus; 16S rRNA gene profiling; community state types; probiotic; vaginal microbiota.

Figure 1.

Diagram of study design and flow.

Figure 2.

PCA plots obtained using the relative abundances of bacterial taxa in each vaginal swab. Each point in the plots indicates a single vaginal swab. The color of each dot in the plots indicates the CST of the sample according to the legend reported under the chart; the colors correspond to the colors used in Fig. 3. A, baseline samples (n = 37, i.e. vaginal samples collected at V1 from the 24 volunteers who completed the study and 13 who dropped out); B, all samples (n = 109, i.e. the 37 samples collected at V1 and the samples collected at V2, V3 and V4 from the 24 volunteers who completed the study).

Figure 3.

Composition of the vaginal microbiota of the 24 reproductive-age women who completed the VAG-LPC14 study (see Fig. 1 for details on the study design). The green-white-red heatmap indicates the ages of volunteers; the age in years is indicated in each box. The black-yellow heatmap represents the α-diversity indices, where the color indicates the values from minimum (black) to maximum for each respective index. The green-yellow-red heatmap represents the log₁₀-transformed relative abundances of microbial taxa found in the vaginal bacterial communities. a, CST observed for vaginal samples at each visit; each color corresponds to a specific CST according to the legend reported on the right. Subjects are clustered according to the CST observed at visit 1.

Figure 4.

Relative abundance of vaginal bacterial taxa that were significantly modified during the interventions (n = 24). Volunteers who tested positive for the presence of the probiotic strain LPC-S01 in a vaginal swab are represented in red (S01) and violet (S17). The subject code is indicated for higher-abundance samples. Statistically significant differences were determined according to the Wilcoxon signed rank test. The dotted lines indicate the subjects randomly selected to receive the probiotic first.

Figure 5.

Recovery of L. paracasei LPC-S01 in vaginal swabs. A, histograms indicating the bacterial composition of vaginal swabs as determined by 16S rRNA gene profiling; only volunteers who tested positive for the presence of sequencing reads assigned to the taxonomic group L. paracasei/L. rhamnosus are shown. B, qPCR quantification of L. paracasei LPC-S01 (with strain-specific primers) and total bacteria (with pan-bacterial primers) in fecal and vaginal samples. Samples from which LPC-S01 were isolated on agar plates are shown in the black circle. Only those subjects whose vaginal swabs were positive for LPC-S01 are shown.

Figure 6.

Correlations among the relative abundances of vaginal bacterial taxa calculated at each of the four phases of the trial (i.e. before and after the probiotic and the placebo treatments; n = 24). In addition, correlations with median data at the four time points for each volunteer are shown. The squares with bold black margins highlight the correlations maintained in all five correlation analyses. Only vaginal taxa found in at least 30% of vaginal samples were considered in the analysis. This figure only includes taxa whose abundance significantly correlated with at least one vaginal taxon according to Kendall's tau rank correlation. The colors in the heatmap represent the R-value obtained by Spearman correlation analysis. The asterisks indicate the Kendall's tau rank correlation: *, P < 0.05; **, P < 0.01; ***, P < 0.001.