Genetic diversity of Gardnerella vaginalis in pregnant women diagnosed with intermediate and positive bacterial vaginosis.

Abstract

Bacterial vaginosis (BV) is the main cause of abnormal vaginal discharge in women of reproductive age. Gardnerella vaginalis, has been detected in almost all women with BV. However, there is limited information on the genetic diversity of G. vaginalis isolated from BV intermediate and positive cases. In this study we investigated the genetic diversity of G. vaginalis strains from South African pregnant women. Vaginal swabs were characterized by the Nugent method. A total of n= 87 samples were included in the genetic analysis, (n=50 BV positive) and (n=37 BV intermediate). The presence of G. vaginalis was detected by PCR using bacterium specific 16S rRNA primers. All PCR positive amplicons were sequenced by the Sanger method and the edited sequence data was used for the phylogenetic analysis using the PHYLIP software. The sialidase A gene was amplified by PCR using specific primers and the copy numbers of sialidase A gene was quantified by droplet digital PCR. To assess the diversity of the sialidase A gene, Sanger sequencing was performed. The 16S rRNA gene from G. vaginalis was amplified in all BV positive and BV intermediate samples. All PCR amplicons were successfully sequenced and the nucleotide BLAST results revealed 100% identify to G. vaginalis. The phylogenetic analysis revealed that there is no diversity in G. vaginalis present in BV positive and intermediate cases. The phylogenetic tree of sialidase A sequences from intermediate and positive BV cases revealed two major clades which showed differences related to sialidase A copy number. Quantification of sialidase A showed that the average number of copies per cell was much higher in the BV positive group compared to the intermediate group. Some of the intermediate cases showed high copy numbers for the virulence gene and clustered with the BV positive cases. In the present study the 16S rRNA sequences of the G. vaginalis from BV intermediate and positive women showed that there is no genetic diversity in G. vaginalis detected in BV positive and intermediate samples. The phylogenetic tree of sialidase A gene sequences of intermediate and positive BV revealed two major clades which showed differences related to sialidase A copy number. This data was previously lacking in our setting, especially in a pregnant population. We further demonstrate for the first time that the genetic information present within the sialidase A gene has a direct influence on BV status.