Bacterial vaginosis (BV) is an imbalance of the vaginal
microbiome that can lead to adverse health outcomes, including increased
likelihood of potential pathogens colonizing the vagina, yet the mechanisms
underlying these processes are poorly understood. A study published in PLOS Biology by Amanda Lewis at
University of California, San
Diego, and colleagues suggests that mutually beneficial relationships between
different species of vaginal bacteria may encourage growth of potentially
harmful pathogens, such as the common oral bacterium Fusobacterium nucleatum.
The work challenges the belief that a suitable living environment supporting
pathogen colonization is created solely by the absence of healthy bacteria, and
may explain prior clinical links between oral sex and BV.
Approximately 29% of women in the United States are
affected by BV, putting them at risk for adverse health outcomes such as
preterm labor and amniotic fluid infections during pregnancy. To analyze
interaction between bacterial
communities and the ability of different bacteria to access
required nutrients in an already-occupied microbiome, Lewis and colleagues
conducted experiments in human vaginal specimens and in mice. The authors
inoculated mice or mouse vaginal communities with F. nucleatum and found
evidence of increased biochemical activities previously linked with BV, such as
the enzyme sialidase. After performing models in mice, the authors conducted
similar experiments in which Fusobacterium nucleatum, a bacterium found in the
mouth and linked with gum disease, intrauterine infection and preterm birth,
was inoculated into human vaginal microbial communities cultivated from vaginal
swabs of twenty-one women. Samples incubated with Fusobacterium displayed
higher levels of multiple key indicators of BV compared to the identical
women's microbiomes incubated without Fusobacterium.
The experiments led to the discovery that Fusobacterium
nucleatum does not act in a simple one-way relationship with other bacteria,
but may engage in a mutually beneficial relationship, potentially encouraging
dysbiosis (microbial imbalance) in susceptible vaginal communities.
Fusobacterium was helped by bacteria in BV-like communities that produce an
enzyme called sialidase, enabling Fusobacterium to consume sialic acids from
mucus produced by the host. Fusobacterium also acted by unknown mechanisms to
greatly benefit the growth of Gardnerella vaginalis, a sialidase producer
believed to be a key player in BV.
The researchers demonstrated that mutual benefit between
bacteria species may promote pathogen colonization of the vagina and encourage
features of vaginal dysbiosis. However, additional studies are needed to
develop modes of prevention or treatment of BV in women. Fusobacterium is
widespread in human mouths and overgrows in dental plaque; the authors
speculate that it may be introduced during oral
sex, which has been identified in some clinical studies as a risk factor for
BV.
.png)
.jpg)
.gif)
