Vaginal microbiome of vulvovaginal candidiasis

Variable patterns of the vaginal microbiome (VMB) are found in patients with vulvovaginal candidiasis (VVC) , according to a review, thus challenging the notion of a protective role for lactobacilli.¹

The VMB may be a biological barrier to pathogenic microorganisms. There is also an increased risk of acquiring various vaginal pathogens when the dominant lactobacilli community is disrupted.

The special section on the vaginal microbiome in the Journal of Lower Genital Tract Disease was written on behalf of the International Society for the Study of Vulvovaginal Disease (IISVD).

“Despite the uncertain effect of lactobacilli in vivo, a majority of in vitro and animal studies have shown that Lactobacilli species exerts an inhibitory effect on the growth, morphological transition, virulence, and biofilm formation of Candida albicans (C. albicans),” wrote the authors.

The metabolites of Lactobacilli species have been shown to have antifungal properties. But only specific lactobacilli strains can produce these metabolites in sufficient quantities needed for antifungal activity, which potentially explains the failure of vaginal lactobacilli to suppress Candida colonization.

For instance, physiological levels of lactic acid may be too low to inhibit Candida species overgrowth; if so, the role of lactic acid for the control of its overgrowth is unclear.

Still, lactic acid at physiological concentrations could increase the efficacy of azoles against C. albicans, and at higher concentrations against C. glabrata.

Numerous studies in women with VVC have reported a relative overrepresentation of L. iners and a relative underrepresentation of hydrogen-peroxide producing lactobacilli.

Study dissimilarities in the relationship between VMB and VVC may be due to different patients' geography, age and symptoms. Approaches used for sample collection, processing and identification may also differ.

Lower numbers of lactobacilli as a causative factor in Candida species vaginitis after antibiotic therapy has been proposed. Yet not all studies support the link between VVC and antibiotic usage. Evidence is also lacking about an association between reduction or loss of function of lactobacilli or other bacteria and antibiotic therapy.

Two treatment options under investigation for recurrent VVC are immunotherapy and vaccination.²

However, since the advent of nucleic acid amplification tests to diagnose Candida species, the standard diagnostic tests of culture with Sabouraud agar are less appealing. “Molecular tests are far more sensitive, result in a short turnaround time, and enable the possibilities for self-testing and the diagnosis of coinfections,” wrote the authors.

On the other hand, molecular tests can render false-positive results in patients with a low probability for infection and identify asymptomatic Candida that does not require treatment. The costs are also higher than for microscopy.

The authors advocate additional longitudinal studies to elucidate the connection between the host and the bacterial and fungal components of the VMB. This will enable insight into the potential interactions and antifungal mechanisms of vaginal lactobacilli; also, to understand their role in VVC.

References

1. De Seta F, Lonnee-Hoffmann R, Chen L, et al. The vaginal microbiome: III. The vaginal microbiome in various urogenital disorders. J. Low Genit Tract Dis. Special section – the vaginal microbiome. January 2022; 26(1); p 85-92.
2. Rosati D, Bruno M, Jaeger M, et al. Recurrent vulvovaginal candidiasis: an immunological perspective. Microorganisms 2020;8:1–14.