Changes in Neighbouring Microbiota in Genitourinary Syndrome

Problems addressed by the study:

Genitourinary syndrome (GUS) is a common disorder during menopause, reported to be at least 50% in many series, which reduces quality of life. Unfortunately, despite being such a common disorder, patients do not report their complaints about this issue and clinicians do not question patients about this condition (NAMS, 2020). There is little awareness about the subject and relatively few studies on the pathophysiology and treatment of the disease.

GUS is diagnosed clinically. Symptoms such as vulvovaginal dryness, burning or irritation; dyspareunia; and symptoms such as urge incontinence, dysuria or recurrent urinary tract infections are observed in the urinary system (NAMS, 2020). Urinary symptoms of GUS, such as dysuria, are often confused with recurrent urinary tract infections. The pathophysiology of GUS is often attributed to estrogen deficiency, but some researchers suggest that these changes may also be related to the vaginal microbiome (Hummelen et al., 2011). Because while estrogen deficiency is present in all women who enter menopause, GUS is observed in a certain portion. Therefore, our study will contribute to the literature aimed at shedding light on the pathogenesis.

Although there are both vaginal and urinary symptoms in GUS, the most studies are on vaginal microbiota. There is only one study on urinary microbiota (Lillemon et al., 2022). There is no study evaluating the periurethral microbiota.

Is there a relationship between vaginal microbiota and GUS symptoms?

The relationship between vaginal microbiota and GUS has been addressed in many studies. Various changes occur in the vaginal flora during menopause due to the decrease in estrogen hormone during menopause. Gustafsson et al. (2011) reported that women of reproductive age were more frequently colonized with L. crispatus compared to menopausal women. Similarly, premenopausal women had significantly higher free glycogen levels and higher Lactobacillus levels compared to postmenopausal women (Zhang et al., 2012; Mirmonsef et al., 2014).

Studies on patients with GUS symptoms have shown that women with mild GUS symptoms were more likely to be predominantly Lactobacillus species in the vagina and had lower bacterial diversity, whereas in more severe GUS cases, colonization with Lactobacillus species was reduced and there was greater bacterial diversity (Brotman et al., 2018). Species detected in the group with increased bacterial diversity included Prevotella, Porphyromonas, Peptoniphilus and Bacillus (Brotman et al., 2018). Notably, CST IV-A colonization was more prevalent in the vagina in women with the most severe GUS symptoms (Hummelen et al., 2011, Brotman et al., 2018).

In the studies summarized here, a vaginal microbiota dominated by Lactobacillus species was detected in all women receiving hormone replacement therapy or local estrogen therapy, suggesting that estrogen levels have an effect on the vaginal bacterial community and structure. However, whether GUS symptoms are reduced by estrogen-related changes or by changes in the vaginal flora is still controversial. Although many studies have shown that Lactobacillus dominance in the vaginal microbiota is negatively associated with GUS symptoms, studies have recently been published showing that this is not the case. Mitchell compared 3 groups given local estrogen, vaginal lubricant, and placebo in their study (Mitchell, 2018). GUS complaints decreased in all three of these groups; vaginal estradiol -1.4 (95%CI, -1.6 to -1.2); moisturizer, -1.2 (95%CI, -1.4 to -1.0); and placebo, -1.3 (95%CI, -1.5 to -1.1). Although the amount of Lactobacilli increased significantly in the local estrogen group compared to the other groups, the similar decrease in complaints cannot be explained by both estrogen and microbiota hypotheses.

We planned to use 2 different control groups in our study to investigate this issue. Patients without any GUS symptoms and without vulvovaginal atrophy findings on examination will be the first control group, and patients without complaints but with vulvovaginal atrophy findings on examination will be the second control group. Examining whether there is a difference in colonization in these two groups will be the first in the literature and will contribute to the literature in terms of elucidating the pathogenesis.

As mentioned before there are both vaginal and urinary symptoms in GUS. So is there a relationship between vaginal microbiota and periurethral and urinary microbiota? There is a study on this subject that examined both vaginal and urinary microbiota. In the study, local estrogen treatment neither caused a significant decrease in GUS symptoms nor caused a change in vaginal and urinary microbiota (Lillemon et al., 2022). In this study, Lillemon and his team examined the effect of local estrogen treatment on vaginal and urinary microbiota separately and did not examine whether there were similarities or differences between the two environments. In addition, since they included patients who were generally in menopause and not those with only GUS complaints in the study, local estrogen treatment was found to be unsuccessful. Yet, local estrogen treatment is the first-line treatment after lubricants in GUS and is a successful treatment method in 85% of patients (NAMS, 2020). Since they used a general menopausal population in the study, there may not have been a significant difference in microbiota between patients taking estrogen and those not taking it, and a significant decrease in GUS complaints in those taking local estrogen.

There is no study comparing vaginal microbiota with periurethral microbiota in GUS. However, there is a study which compares the periurethral and urinary microbiota of women of reproductive age that showed that both environments change after menstruation and intercourse, and as a result, these environments are dynamic and variable like the vaginal microbiota (Price, 2020). Again, urinary, periurethral, vaginal and fecal microbiota were examined in women of reproductive age, urinary microbiota was compared with fecal, and urinary microbiota was shown to be more variable compared with fecal microbiota. However, no comments were made about vaginal and periurethral microbiota in this study (Biehl, 2022). Therefore, our study will be the first to compare these 3 environments in GUS.

Why is periurethral microbiota important?

When we examine the GUS complaints of patients, the situation they describe as pain during intercourse is mainly the pain they feel at the entrance to the vagina, in the introitus. Since this area is close to the skin, we think that bacterial colonization may be different from vaginal colonization. In this patient group, the introitus is generally observed to be more red during examination. This also suggests that aerobic vaginitis agents are more intense in this area. Waetjen has shown in his latest study that there is a density of Streptococcus in the vaginal microbiota of patients with dyspareunia (Waetjen, 2023).

Our hypotheses in this study are: 1-there is a relationship between the vaginal-periurethral and urinary microbiota. 2- Lactobacillus colonization increases in areas outside the vagina with local estrogen treatment. 3- The severity of GUS symptoms is higher in patients with a microbiota predominant by facultative anaerobic bacteria such as Staphylococcus or Streptococcus.