Dr Cindy Liu from George Washington University presented interesting findings on the vaginal microbiome today.
The term ‘dysbiosis’ refers to an ecological imbalance in the microbiome that impairs health. It moves away from the classic concept of infectious disease as being caused by a single pathogen, and moves toward the appreciation of disease as disruption to a complex, dynamic ecosystem. Disruptions might be the loss of ‘good’ bacteria, dominance of ‘bad bacteria’, but the imbalance leads to events that impair function, or induce inflammation.
Earlier today, Liu described anaerobic penile dysbiosis: the polymicrobial colonisation of the subpreputial space with anaerobic flora, and its role in HIV acquisition. In her afternoon session, she built on this to describe one of the classic vaginal dysbioses: bacterial vaginosis (BV). BV is characterised by the overgrowth of anaerobic microflora, and reduction of Lactobacilli, and is therefore a vaginal anaerobic dysbiosis. BV is a common condition, and its management is characterised by persistence, recurrence. It is also associated with an increased risk of HIV acquisition, as well as a range of adverse pregnancy outcomes and pelvic inflammatory disease.
What is the relationship between these penile and vaginal anaerobic dysbioses? Are these phenomena sexually transmissible? The anaerobic organisms implicated in both processes certainly have considerable overlap, and evidence from several quarters supports the sexual transmission of BV.
Liu and her colleagues enrolled 165 uncircumcised HIV-negative Ugandan men and their female partners into the Rakai Health Sciences Cohort. Self-obtained vaginal swabs from female partners were assessed for BV using the Nugent score, while swabs from the coronal sulcus were collected from men for assessment of their microbiome using 16S rRNA amplification.
Penile microbiomes were found to fit into four distinct patterns, termed Community State Types, which ranged from microbiomes with low diversity and few anaerobes (CST 1-3) to communities with very high diversity and a rich population anaerobic flora (CST 4-7): so called anaerobic dysbiosis.
Bacterial vaginosis was found more frequently among female partners of men with anaerobic dysbiosis than in men with lower levels of diversity and less anaerobic flora. This supports the hypothesis that anaerobic penile and vaginal dysbiosis are sexually transmissible and results from sharing of anaerobes within heterosexual settings.
Longitudinal studies are needed to prospectively observe transmission events between couples, as well as account for potential confounders such as hormonal factors, hygiene practices and so on. Higher resolution molecular identification tools to better describe phylogenetic relationships between organisms shared by the partners are needed to confirm transmissibility.