Identification, quantification and subtyping of Gardnerella vaginalis in noncultured clinical vaginal samples by quantitative PCR

Gardnerella vaginalis is an important component of the human vaginal microflora. It is proposed to play a key role in the pathogenesis of bacterial vaginosis (By), the most common vaginal condition. Here we describe the development, validation and comparative analysis of a novel molecular approach capable of G. vaginalis identification, quantification and subtyping in noncultured vaginal specimens. Using two quantitative PCR (qPCR) assays, we analysed G. vagina/is bacterial loads and clade distribution in 60 clinical vaginal-swab samples. A very high pathogen prevalence was revealed by species-specific qPCR not only among BV patients (100%), but also in healthy women (97%), although the G. vagina/is concentration was significantly lower in non-BV samples. G. vagina/is clades identified in vaginal specimens by subtyping multiplex qPCR, which targets four clade-specific genetic markers, had frequencies of 53% for clade 1, 25% for clade 2, 32% for clade 3 and 83% for clade 4. Multiple clades were found in 70% of samples. Single G. vagina/is clades were represented by clade 1 and clade 4 in 28% of specimens. A positive association with BV was shown for clade 1 and clade 3, while clade 2 was positively associated with intermediate vaginal microflora, but not with BV. Clade 4 demonstrated no correlation with the disorder. The presence of multiple clades had a high positive association with BV, whereas G. vagina/is identified as a single clade was negatively linked with the condition. Polyclonal G. vagina/is infection may be a risk factor for BV.