Genetic heterogeneity and taxonomic diversity among Gardnerella species

Abstract

Gardnerella spp. are the most frequent organisms found in bacterial vaginosis (BV). However, colonization by Gardnerella spp. does not always lead to BV. Developments in molecular genetics have shed new light on the diversity of the genus Gardnerella, leading to an emended description of Gardnerella vaginalis and, for the first time, the inclusion of more species of Gardnerella, namely, Gardnerella leopoldii, Gardnerella piotii, and Gardnerella swidsinskii. While no association had been made between the novel Gardnerella species and virulence potential, there is genomic evidence of a higher prevalence of some genotypes in BV cases, as compared with colonization in women in whom BV has been clinically ruled out. Gardnerella vaginalis has been considered a pivotal player in the progression of bacterial vaginosis (BV), a condition associated with serious health complications. However, G. vaginalis is also commonly found in asymptomatic or BV-negative women. This has generated interest in the question of whether genetic differences among isolates might distinguish pathogenic from commensal isolates. G. vaginalis was the only recognized species in its genus for four decades, but recently an emended description of G. vaginalis and descriptions of three new species Gardnerella leopoldii, Gardnerella piotii, and Gardnerella swidsinskii have been proposed. This review provides background on the heterogeneity and diversity within the genus Gardnerella, highlighting the main features that distinguish species and clades, and how these features may impact BV development.