A cervicovaginal microbiota with few Lactobacillus and rich in anerobic strains is associated with an increased risk of complications in pregnancy, infertility, sexually transmitted disease, etc. This profile was found to be more common among sub-Saharan women than Western women.
The risk of gynecological diseases, complications during gestation and sexually transmitted diseases, is partly influenced by the local bacterial community. Microbiomes dominated by L. iners or L. crispatus, frequent in sub-Saharan women much more than in the Western world, would seem to migrate to high-risk profiles with a greater presence of anaerobic strains and low in lactobacilli with the related consequences.
A manipulation of the bacterial pattern aimed at restoring physiological profiles could therefore help to prevent women’s health problems still common and little considered among those populations.
This is the result of a study by Alexander Munoz and colleagues from Harvard Medical School (Boston, USA), recently published in Microbiome.
The cervicovaginal microbiota influences the gynecological health of women, but also the good course of pregnancy and any sexually transmitted disease, including HIV.
Among South-African and South-Saharan women gathered in study courts, most showed a diverse bacterial population, but characterized by a low presence of Lactobacillus, but high presence of Gardnerella vaginalis or Prevotella.
In contrast, a minority showed good expression of these species, L. crispatus and L. iners in particular.
Contrary trend in European and American Caucasian women who instead showed bacterial profiles or cervicotypes (CTs) mainly dominated by lactobacilli.
Considering how common profiles among African women are correlated with an increased risk of developing gestational diseases and complications and how the rearrangement towards a potentially harmful composition has not been explored yet, in this study the dynamics of transition were investigated focusing on the main actors involved.
To do so, cervicovaginal microbiota swabs from 88 healthy women at baseline and followed for, on average, 9 months (316 samples in total) were periodically collected and analyzed.
The bacterial composition was then characterized by 16S rRNA gene sequencing and the profiles classified into the 4 commonly accepted cervicotypes (CTs) according to the predominant species (CT1 if dominated by L. crispatus; CT2 dominated by L. iners; CT3 dominated by G. vaginalis; CT4 dominated by Prevotella). The main results are as follows.
A first comparison of the samples over time and clinical conditions showed a widespread rearrangement with a general increase in diversity within the various CTs. In particular:
– women with CT1 showed migration toward CT2, from CT2 to CT3 and CT4. Direct transitions from CT1 to CT3-4 or in the opposite direction (from CT3-4 to CT2 or 1) were more rare as confirmed by probabilistic mathematical models
– women already in CT3-4 at baseline have instead shown greater stability over time compared to the other CTs, which were instead more mobile.
– the CT2 profile would seem to be the intermediary between communities associated with positive outcomes (CT1) and those with higher risk and high diversity (CT3-4)
– within the CT2 group, samples that showed the highest values of alpha diversity were also those most prone to a transition to CT3
Once the transition probabilities were determined under spontaneous conditions, simulating a usual clinical setting, the effects of a single external factor in the subsequent distribution of CTs were explored further.
Despite destabilizing interventions, none were shown to affect the bacterial community in the long term. However, CT1 (L. crispatus) was found to be the most susceptible to these disturbances with a longer duration over time.
Once the transient nature was observed, the impact of any transitions was evaluated. Among all interventions, those targeting CT1-CT2 were most successful, supporting the hypothesis that targeted manipulations on L. crispatus and L. iners may increase the number of women with a low-risk CTs profile.
To summarize, this study helps to understand the temporal dynamics of the cervicovaginal microbiota of African women by identifying the transient nature of the bacterial community dominated by L. crispatus (CT1) and L. iners (CT2) and suggesting targeted interventions to promote its rearrangement towards a CT1 profile.
A predominance of L. crispatus has indeed shown better protection for women’s health. Current treatments, mainly antibiotic-based, do not seem to favor this transition.
Targeted interventions would therefore be the best strategy in terms of prevention and treatment of gynecological disorders and possible complications in pregnancy.
English