Oral microbiome changes associated with the menstrual cycle in healthy young adult females

Abstract

The relationship between the menstrual cycle and the oral microbiome has not been clarified. The purpose of this study was to assess potential changes in the oral microbiome of healthy young adults using 16S rRNA-based sequencing. Eleven females (aged 23-36 years) with stable menstrual cycles and without any oral problems were recruited. Saliva samples were collected before brushing every morning during the menstrual period. Based on basal body temperatures, menstrual cycles were divided into four phases, namely the menstrual, follicular, early luteal, and late luteal phases. Our results showed that the follicular phase had a significantly higher abundance ratio of the Streptococcus genus than the early and late luteal phases, whereas the abundance ratios of the Prevotella 7 and Prevotella 6 genera were significantly lower in the follicular phase than those in the early and late luteal phases and that in the early luteal phase, respectively. Alpha diversity by the Simpson index was significantly lower in the follicular phase than that in the early luteal phase, and beta diversity showed significant differences among the four phases. Using the relative abundance data and copy numbers of the 16S rRNA genes in the samples, the bacterial amounts in the four phases were compared, and we observed that the follicular phase had significantly lower amounts of the Prevotella 7 and Prevotella 6 genera than the menstrual and early luteal phase, respectively. These results indicate reciprocal changes with the Streptococcus genus and Prevotella genera, particularly in the follicular phase. In the present study, we showed that the oral microbiome profiles are affected by the menstrual cycles of healthy young adult females.

Keywords: Prevotella; Streptococcus; menstrual cycle; oral microbiome; saliva.

Figure 1

Abundance ratios of the top 20 bacteria genera in the oral microbiome. Stacked bar plots showing the composition of the most dominant genera color-coded and ranked according to abundance, while Prevotella 6 and Prevotella unnumbered genera were arranged next to Prevotella 7 genus. The abundance ratios in females are shown in four phases: menstrual, follicular, early luteal, and late luteal phases. The abundance ratios in males are shown with four durations corresponding to the number of days: days 1–2, 1^st duration; day 14, 2^nd duration; days 21–22, 3^rd duration; day 28, 4^th duration. Females, N = 9; Males, N = 5.

Figure 2

Abundance ratios of each bacterial genus in the oral microbiome of female subjects. Boxplots showing the abundance ratios of each bacterial genus during menstrual cycles: (A) Streptococcus genera. (B) Prevotella 7 genera. (C) Prevotella 6 genera, (D) Saccharibacteria genera, (E) Atopobium genera, and (F) Oribacterium genera (menstrual, follicular, early luteal, and late luteal phases). Friedman test and Bonferroni test, ^* P <0.05 and ^** P < 0.01. N = 9.

Figure 3

Bacterial diversity. (A) Box plots showing the alpha diversity indices, Simpson, Shannon, and Chao1, based on the phases of the menstrual cycles (menstrual, follicular, early luteal, and late luteal phases) or durations (days 1–2, 1^st duration; day 14, 2^nd duration; days 21–22, 3^rd duration; day 28, 4^th duration). Friedman test and Bonferroni test, ^* P <0.05. Females, N = 9; Males, N = 5. (B) Nonmetric multidimensional scaling plot showing the dissimilarities of all samples collected in this study according to menstrual cycles (menstrual, follicular, early luteal, and late luteal phases). Ellipsoids represent a 95% confidence interval used to group each sample.

Figure 4

Copy numbers of the 16S rRNA gene collected by saliva samples. Data is shown in box plots. Friedman test and Bonferroni test. Females, N = 9; Males, N = 5. The vertical axis was a base-10 log scale. rRNA, ribosomal RNA.

Figure 5

Amounts of dominant bacteria genera in the oral microbiome of female subjects. Box plots showing the amounts of (A) Streptococcus, (B) Prevotella 7 genera, (C) Prevotella 6, and (D) Saccharibacteria genera during the menstrual cycles. Friedman test and Bonferroni test, *P < 0.05 and ^** P < 0.01. N = 9.