Strain-level heterogeneity in Gardnerella urinary tract persistence and pathogenesis in an in vivo model is consistent with comparative phylogenomic analyses.

backgroundGardnerella is a bacterial genera commonly present in the female urogenital tract, especially in bacterial vaginosis. Gardnerella are frequently detected in urine collected directly from the bladder and have been implicated in urinary incontinence and recurrent urinary tract infections. Understanding the contribution of Gardnerella to pathogenesis is complicated by its genetic heterogeneity and a shortage of data from in vivo models. One clinical isolate of Gardnerella triggered urothelial exfoliation and promoted urinary tract infection by uropathogenic E. coli in a mouse model. This study was designed to compare diverse Gardnerella strains in vivo to identify genomic variation associated with urinary tract persistence and pathogenesis.

methodsEighteen Gardnerella strains from the four main clades were inoculated transurethrally into female C57BL/6 mice. Bacteriuria was monitored by quantitative culturing and pathologic features were assessed in bladder tissues. Pan-genome phylogenetic analyses were performed to identify genes associated with in vivo phenotypes, including long- and short-term bacteriuria, urothelial exfoliation, and edema. Genes that were significantly associated to phenotype were matched against a pangenome analysis of 291 publicly available Gardnerella genomes to determine the conservation of these putative colonization and virulence factors across the genus.

resultsClade 2 strains were more persistent, whereas the other three clades caused transient bacteriuria or were undetectable. Clade 2 and 4 strains induced urothelial exfoliation, and clades 2, 3 and 4 triggered edema. Forty-five genes were significantly associated with persistence and pathogenicity. Among the 291 publicly available genomes, clade 2 strains encoded more of the bacteriuria-associated genes than strains in the other three clades. Exfoliation-associated genes were present in most clade 4 strains. Clade 3 strains lack most of the in vivo associated genes, whereas clade 1 strains were more heterogeneous.

conclusionsThis study provides in vivo evidence for differential urinary tract colonization and pathogenesis by different clades/species within the genus Gardnerella and identifies new putative persistence and virulence factors. Pangenome analysis predicted that clade 2 Gardnerella are the most likely to persist in the urinary tract and that clades 2 and 4 have the highest uropathogenic potential. These findings inform future targeted screening and treatment approaches aimed at limiting harmful Gardnerella urinary tract exposures.