The vaginal microbiome plays a crucial role in women’s health, with certain microbial species linked to various adverse outcomes. Among these, Gardnerella species have been identified as significant risk factors for conditions such as sexually transmitted diseases (STDs), cervical cancer, bacterial vaginosis, and notably, preterm birth.
Gardnerella produces sialidase, an enzyme that degrades protective mucins in the vagina, thereby increasing host inflammatory responses. Despite its association with these negative health outcomes, Gardnerella can be present in the vaginal microbiome without necessarily causing symptoms or disease.
About the Study
Researchers at Jimei University in Xiamen, China, have developed a computer technique to identify Gardnerella clades and species in the vaginal microbiomes of pregnant women. The study aimed to assess the abundance of Gardnerella and its association with preterm births.
The study utilized shotgun metagenomic sequences from three cohorts: the Multi-Omic Microbiome Study: Pregnancy Initiative (MOMS-PI), the UAB-enriched cohort, and the Stanford-enriched cohort. This provided 781, 45, and 62 samples from 231, 15, and 20 individuals, respectively. An additional MOMS-PI-enriched cohort included 145 samples from 42 individuals to match the Gardnerella abundance distributions of the UAB and Stanford-enriched cohorts.
The researchers developed and validated a method to detect Gardnerella species from vaginal microbiomes, assessing the abundance of six clades comprising 14 genomic species from the collected samples.
Study Findings
The study revealed that individual microbiomes often contained multiple Gardnerella variants. Clade counts were directly proportional to microbial burdens and non-human to human genetic reads ratios, suggesting a potential link between Gardnerella abundance and preterm birth risk.
Consistent taxon co-occurrences were observed among Gardnerella genetic clades and study cohorts. Some previously uncommon variants were identified in additional cohorts, highlighting the importance of surveying multiple individuals to capture Gardnerella diversity.
In October 2020, researchers constructed a Gardnerella core-genome phylogeny using GenBank assemblies. Among 12,105 pangenome genes, 85 core genes were identified. Gardnerella had a median relative abundance of 17% in the unenriched MOMS-PI cohort and 45% in the enriched cohort.
The genomic census supported 14 Gardnerella genomic species and six different clades, including four previously reported clades and two new isolate-based clades. Four strain groups were identified: G. vaginalis, GS4 Gardnerella piotii, GS5 G. leopoldii, and GS6 Gardnerella swindinskii. Additionally, four Gardnerella amplicon sequence variations (ASVs) were categorized into evolutionary groups G1, G2, G4, and G5.
Similar trends in Gardnerella variant richness and prevalence were observed across cohorts. Clades one through four were more common than clades five and six. The third clade was particularly prevalent among African American individuals, while the fifth and sixth clades, though less common overall, were abundant in the UAB-enriched cohort.
Patterns of Gardnerella coexistence were consistent across clades, with enriched cohorts showing greater average relative abundances. Preterm delivery was linked to increased Gardnerella richness and microbial burden, but no significant correlation changes were observed across all four cohorts.
Conclusions
The study concluded that the vaginal microbiomes of pregnant women contain diverse Gardnerella variants, with numerous clades present within individual microbiomes, indicating high diversity within the species. The number of clades was associated with higher microbial load, suggesting a potential link between Gardnerella diversity and microbiota composition.
Six clades and 14 genomic species were identified across three cohorts, with the most well-characterized clades appearing most frequently. Multiple Gardnerella strains were detected within single vaginal microbiomes, demonstrating the reliability of the detection method.
Gardnerella species are common in vaginal microbiomes, with certain species occurring more frequently in specific populations. Further research is necessary to better understand the ecological roles, interactions, and impacts of these species on microbial ecosystems, preterm births, and overall health outcomes.
Implications for Future Research and Public Health
This study underscores the importance of microbial diversity in understanding health outcomes. The identification of specific Gardnerella clades associated with preterm birth risk highlights the need for targeted interventions and personalized medical approaches. By advancing our understanding of the vaginal microbiome’s role in pregnancy and preterm birth, rese
