NEW YORK (GenomeWeb) – Distinct microbial communities call different parts of the female reproductive tract home, according to a new sequencing study.
While previous studies had found that the vaginal microbiome primarily contained Lactobacillus, the upper reproductive tract — which includes the uterus and fallopian tubes — had widely been thought to be microbe-free and sterile in healthy people.
To explore the microbial composition of the female reproductive tract, a BGI-Shenzhen-led team of researchers collected samples from about a hundred women for 16S rRNA sequencing. As the team reported in Nature Communications today, it found that there was a continuum of microbes along the female reproductive tract. The team also found that certain microbes were more common among women with adenomyosis or endometriosis-linked infertility.
"The study … suggests that surveying the vaginal or cervical microbiota might be useful for detection of common diseases in the upper reproductive tract," BGI-Shenzhen's Huijue Jia and her colleagues wrote in their paper.
The researchers collected microbiome samples from six sites along the female reproductive tract — from the vagina to the cervical mucus to the fallopian tubes —from 95 women. Some of the samples, such as from the vagina or cervix, were collected from the women during a clinic visit. Others, such those obtained from the uterus, were collected during laparoscopy or laparotomy, to avoid contamination with the lower, vaginal microbiome. These women were undergoing surgery for conditions not thought to be associated with infections.
The samples then underwent 16S rRNA gene amplicon sequencing and clustering into operational taxonomic units.
In a principal components analysis, samples from the upper and lower reproductive tract formed two clusters. The lower vaginal and posterior fornix samples were vastly dominated by species from the Lactobacillus genus, while the cervical mucus had a lower proportion of Lactobacillus species. Lactobacillus species were present to a smaller degree among the endometrium samples and even less abundant among the fallopian tube samples.
At the phylum level, the researchers found that Firmicutes dominated the lower reproductive tract samples, while the upper reproductive tract harbored high proportions of Proteobacteria, Actinobacteria, and Bacteroidetes. Overall, they noted that the upper part of the tract had increased bacterial diversity, though lower levels of bacterial biomass.
The researchers also attempted to culture bacteria from samples they collected from an additional 15 women. They were able to generate cultures from five of the women, suggesting that live bacteria were present at these sites and challenging the notion of those sites being sterile.
Some sites had signature OTUs, Jia and her colleagues reported. For instance, L. iners and L. crispatus were indicative of vaginal sites, whereas Pseudomonas, Erysipelothrix, and Facklamia were suggestive of the fallopian tubes. The cervical mucus and endometrium didn't have signature OTUs, leading the researchers to say they might be transition zones.
In addition, the researchers noted that some microbial states correlated with disease. Hysteromyomas, benign uterine tumors, were associated with a decreased abundance of Lactobacillus species in vaginal and cervical samples, as compared to those without hysteromyomas. However, L. iners was more common among cervical mucus samples from women with hysteromyomas.
The microbes present could distinguish women with or without endometriosis-related infertility, suggesting that the microbiome could be used to detect a number of diseases affecting women.
"How disturbances to the vagino-uterine microbiota might eventually lead to benign or malignant conditions threatening the health of pre-menopausal and post-menopausal women is a major open question," the researchers wrote.