Resolution and Cooccurrence Patterns of Gardnerella leopoldii, G. swidsinskii, G. piotii, and G. vaginalis within the Vaginal Microbiome

Abstract

Gardnerella vaginalis is a hallmark of vaginal dysbiosis, but it is found in the microbiomes of women with and without vaginal symptoms and those who do not have microbiologically defined dysbiosis. G. vaginalis encompasses diverse taxa differing in attributes that are potentially important for virulence, and there is evidence that clades or subgroups within the species are differentially associated with clinical outcomes. The G. vaginalis species description was recently emended, and three new species within the genus were defined (G. leopoldii, G. swidsinskii, and G. piotii). 16S rRNA sequences for the four Gardnerella species are all >98.5% identical, and no signature sequences differentiate them. We demonstrated that Gardnerella species can be resolved using partial chaperonin 60 (cpn60) sequences, with pairwise percent identities of 87.1 to 97.8% among the type strains. Pairwise cooccurrence patterns of Gardnerella spp. in the vaginal microbiomes of 413 reproductive aged Canadian women were investigated, and several significant cooccurrences of species were identified. Abundance of G. vaginalis and G. swidsinskii was associated with vaginal symptoms of abnormal odor and discharge. cpn60 barcode sequencing can provide a rapid assessment of the relative abundance of Gardnerella spp. in microbiome samples, providing a powerful method of elucidating associations between these diverse organisms and clinical outcomes. Researchers should consider using cpn60 instead of 16S RNA for better resolution of these important organisms.

Gardnerella vaginalis as a Cause of Bacterial Vaginosis: Appraisal of the Evidence From in vivo Models

“…In another mouse model, the clade 2 strain JCP8151B was shown to result in colonization and live recovery of Gardnerella, clue-like cells with adherent Gardnerella, an epithelial exfoliation response similar to that seen in humans, and higher levels of the hydrolytic enzyme sialidase together with biochemical evidence of mucus degradation, similar to that seen in BV (Gilbert et al, 2013;Lewis et al, 2013). The recent suggestions for new species names for subsets of Gardnerella strains seems to place the JCP8151B strain within the subset of clade 2 strains being referred to as Gardnerella piotii (Hill et al, 2019;Vaneechoutte et al, 2019). In short, the experimental evidence points to the conclusion that G. vaginalis and G. piotii (if this naming scheme is adopted by the field) can cause clinical signs of BV when introduced into human and animal hosts.…”

“…Of note, primer sets that target variable regions 1 and 2 of the gene encoding 16S often see lower relative levels of Gardnerella in women with BV when compared to studies that target variable regions 3 and/or 4 or that use culture-based studies (Graspeuntner et al, 2018). It has been recently emphasized that 16S gene sequences cannot differentiate the genetically divergent subsets of Gardnerella and that other methods (e.g., cpn60 sequencing) are more effective in this regard (Hill et al, 2019). Regardless of the method used to detect Gardnerella in women, whether the organism is a causal factor in BV cannot be determined by observational study.…”

A generalist lifestyle allows rareGardnerellaspp. to persist at low levels in the vaginal microbiome

“…piotii (Subgroup B/Clade 2) [3,4]. These Gardnerella species differ in their phenotypic traits, including sialidase activity and vaginolysin production, which may render some of the subgroups more pathogenic than the others [5][6][7].…”

“…The relative abundances of these co-occurring species, however, are not equal. Subgroup A (G. swidsinksii and G. leopoldii) and subgroup C (G. vaginalis) are most frequently dominant in reproductive aged women [4,8]. These two subgroups are also often associated with the clinical symptoms of bacterial vaginosis [4,9,10].…”

“…Subgroup A (G. swidsinksii and G. leopoldii) and subgroup C (G. vaginalis) are most frequently dominant in reproductive aged women [4,8]. These two subgroups are also often associated with the clinical symptoms of bacterial vaginosis [4,9,10]. Subgroup B has been suggested to be associated with intermediate microbiota [7,9,10].…”