Vaginal Microbiota Composition Correlates Between Pap Smear Microscopy and Next Generation Sequencing and Associates to Socioeconomic Status

Abstract

Recent research on vaginal microbiota relies on high throughput sequencing while microscopic methods have a long history in clinical use. We investigated the correspondence between microscopic findings of Pap smears and the vaginal microbiota composition determined by next generation sequencing among 50 asymptomatic women. Both methods produced coherent results regarding the distinction between Lactobacillus-dominant versus mixed microbiota, reassuring gynaecologists for the use of Pap smear or wet mount microscopy for rapid evaluation of vaginal bacteria as part of diagnosis. Cytologic findings identified women with bacterial vaginosis and revealed that cytolysis of vaginal epithelial cells is associated to Lactobacillus crispatus-dominated microbiota. Education and socio-economic status were associated to the vaginal microbiota variation. Our results highlight the importance of including socio-economic status as a co-factor in future vaginal microbiota studies.

Figure 1

Sequencing results compared to the bacterial and other microscopic findings in the Pap smears. The colored bars represent sequencing-based bacterial composition for each subject, other features are based on microscopy of Pap smears. The subjects are grouped based on the microscopy as follows: Group ‘Normal’ represents usual rod-shaped bacteria, ‘Mixed Bacteria’ represents atypical or mixed bacteria without clue cells and ‘BV’ represents subjects with clue cells. Lactobacillus grade (LBG) and modified aerobic vaginitis score (AV) can be found below the bars. Presence of cytolysis (C) and yeast (Y) in the smears are indicated by letters. *Pap smear did not contain enough bacteria for LBG classification.

Figure 2

Average vaginal microbiota composition according to grouping based on microscopic examination of the Pap smears. The dominant species in different groups were L. crispatus for ‘normal’ (40.9%), G. vaginalis for ‘mixed bacteria’ (44.4%) and L. bovis for ‘BV’ (26.7%). The ‘BV’ group is very heterogenous and individual microbiota compositions can be seen in Fig. 1.

Figure 3

Variance partitioning of microbiota community data with respect to technical variables, socioeconomic factors (SES), estimated hormonal status and infection history. The numbers denote the fraction of the total microbiota variance explained by each of the four variable categories. For the list of individual variables within each group, please see the text.