A Complex Microbial Interplay Underlies Recurrent Vulvovaginal Candidiasis Pathobiology

Vaginal mycobiome characteristics and therapeutic strategies in vulvovaginal candidiasis (VVC): differentiating pathogenic species and microecological features for stratified treatment

SUMMARYVulvovaginal candidiasis (VVC) is a prevalent global health burden, particularly among reproductive-aged women. Recurrent VVC affects a significant proportion of this population, presenting therapeutic challenges. The predominant pathogen, Candida albicans, opportunistically transitions from a commensal organism to a pathogen when microenvironmental conditions become dysregulated. Recently, non-albicans Candida species have gained attention for their reduced antifungal susceptibility and recurrence tendencies. Diagnosis is constrained by the limitations of conventional microbiological techniques, while emerging molecular assays offer enhanced pathogen detection yet lack established thresholds to differentiate between commensal and pathogenic states. Increasing resistance issues are encountered by traditional azole-based antifungals, necessitating innovative approaches that integrate microbiota modulation and precision medicine. Therefore, this review aims to systematically explore the pathogenic diversity, drug resistance mechanisms, and biofilm effects of Candida species. Vaginal microbiota (VMB) alterations associated with VVC were also examined, focusing on the interaction between Lactobacillus spp. and pathogenic fungi, emphasizing the role of microbial dysbiosis in disease progression. Finally, the potential therapeutic approaches for VVC were summarized, with a particular focus on the use of probiotics to modulate the VMB composition and restore a healthy microbial ecosystem as a promising treatment strategy. This review addresses antifungal resistance and adopts a microbiota-centric approach, proposing a comprehensive framework for personalized VVC management to reduce recurrence and improve patient outcomes.

Virulence of Candida spp. Isolates From Patients With Recurrent Vulvovaginal Candidosis Is Associated With the Number of Episodes

BACKGROUND

Recurrent vulvovaginal candidosis (RVVC) has been associated with increased antifungal resistance. Recently, we reported that Candida isolates from Colombian patients with RVVC did not show an increase in antifungal resistance.

OBJECTIVE

The aim of this study was to evaluate the virulence of Candida isolates from patients with RVVC.

METHODS

A total of 40 Candida isolates were evaluated (37 C. albicans and 3 C. lusitaniae ). C. albicans isolates were divided into two groups based on the number of VVC episodes in patients per year: Group 1 (four to seven episodes; n = 26) and Group 2 (≥ eight episodes; n = 11). The XTT assay was used to assess biofilm formation. Galleria mellonella larvae were used for survival analysis and fungal load assessment, and the qPCR technique to determine the expression of the PRA1 gene.

RESULTS

It was observed that C. lusitaniae and C. albicans isolates from patients with ≥ eight VVC episodes per year exhibited a greater capacity to form biofilms compared to those from patients with four to seven VVC episodes. Moreover, in the G. mellonella model, larvae inoculated with isolates from RVVC patients exhibited approximately 80% mortality. Similarly, larvae infected with C. albicans from patients who experienced ≥ eight VVC episodes showed a significantly higher fungal load compared to the other evaluated groups; likewise, the expression of the PRA1 gene was significantly higher in isolates from patients with ≥ eight VVC episodes.

CONCLUSION

These results indicate that Candida isolates from patients with RVVC exhibit a high degree of virulence and suggest that virulence may be one of the mechanisms explaining recurrence rather than antifungal resistance itself.

Landscape of in situ cytokine expression, soluble C-type lectin receptors, and vitamin D in patients with recurrent vulvovaginal candidiasis

The immunopathogenesis of recurrent vulvovaginal candidiasis (RVVC) is poorly understood. Recently, it was reported that patients with RVVC present a decrease in both the fungicidal capacity of neutrophils and the proliferative capability of peripheral blood mononuclear cells in response to Candida albicans infection, suggesting an alteration in the innate and adaptive immune response. The aim of this study was to determine the in-situ expression, in the vaginal mucosa, of genes associated with the immune response, as well as the serum concentrations of dectin-1, mannose-binding lectin (MBL), and vitamin D in patients with RVVC. A study was carried out on 40 patients with a diagnosis of RVVC and 26 healthy women. Vaginal scrapings were obtained, and the expression of genes that encode cytokines and transcription factors specific for Th1, Th2, Th17, Treg, pro-inflammatory profiles, and enzymes related to oxidative/microbicidal mechanisms was evaluated by quantitiative polymerase chain reaction (qPCR). Additionally, serum levels of vitamin D and the soluble receptors dectin-1 and MBL were determined by enzyme-linked immunosorbent assay (ELISA). In patients with RVVC, a decreased expression of T-bet, RORγ-T, IL-1β, and IL-17, and an increase in the expression of FOXP3, IL-4, IL-8, IL-10, and IL-18 were observed when compared to healthy women: moreover, decreased levels of MBL were also observed in these patients. These results confirm that patients with RVVC present in-situ alterations in both the specific and adaptive immune response against Candida spp., a fact that could be associated with the exaggerated vaginal inflammatory response.

Patients with recurrent vulvovaginal candidiasis exhibit a decrease in both the fungicidal activity of neutrophils and the proliferation of peripheral blood mononuclear cells

BACKGROUND

Recurrent vulvovaginal candidiasis (RVVC) is an important and underestimated fungal infection.

OBJECTIVE

We aimed to determine the fungicidal and proliferative capacities of neutrophils and peripheral blood mononuclear cells (PBMCs), respectively and the clinical and microbiological characteristics of a cohort of Colombian patients diagnosed with RVVC.

METHODS

A cross-sectional study was conducted. A total of 66 women were included (40 diagnosed with RVVC and 26 healthy women [HW]). Demographic and clinical data were recorded. Vaginal fluid samples were obtained for isolation, identification and antifungal susceptibility testing of Candida species using selective culture media and the Vitek 2.0® system. Blood samples were also obtained to evaluate cell subpopulations; furthermore, neutrophils and PBMCs were isolated to determine their fungicidal and proliferative capacities, respectively.

RESULTS

The median age was 29 (IQR: 34-23) for RVVC and 24 (IQR: 30-23) for HW. Only two species of the genus Candida were identified: Candida albicans (92.5%) and Candida lusitaniae (7.5%). Resistance to fluconazole, voriconazole, flucytosine and amphotericin B was observed on six C. albicans isolates and one C. lusitaniae isolate. Only the family history of vulvovaginal candidiasis was associated with RVVC occurrence. The RVVC group exhibited a significantly higher number of neutrophils but with lower fungicidal activity in comparison to HW; likewise, PBMCs from RVVC patients presented a lower proliferation index when stimulated with C. albicans.

CONCLUSION

Contrary to what has been reported worldwide, in Colombian patients with RVVC, C. albicans was the main isolated species without increased antifungal resistance. The diminished fungicidal and proliferative capacities of neutrophils and PBMCs, respectively, could suggest a possible alteration in the innate and adaptive immune responses.

Bacterial Vaginosis and Vulvovaginal Candidiasis Pathophysiologic Interrelationship

Among the infectious causes of vulvovaginal symptoms, bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC) dominate. Apart from infrequent mixed infections, both are considered independent and caused by unrelated pathogenic mechanisms. Clinical experience, however, is strongly suggestive that in some populations these infections are linked with recurrent BV (RBV) serving as the dominant etiopathogenic trigger for development of recurrent VVC (RVVC) with profound clinical and therapeutic consequences. The biologic basis for this critical interrelationship is discussed and suggests that as a consequence of BV dysbiosis, and not necessarily because of antibiotics prescribed, immune defenses are compromised, neutralizing vaginal yeast tolerance. The consequent BV-induced vaginal proinflammatory environment predisposes to mixed infection or consecutive episodes of post-treatment VVC. Recurrent BV and repeated antimicrobial drug exposure also predispose to acquired fluconazole resistance in C. albicans isolates, contributing to refractory vulvovaginal candidiasis.

The bacterial communities in vagina of different Candida species-associated vulvovaginal candidiasis

The incidence of vaginal infection caused by Candida species has considerably increased over the past two decades. Candida albicans is the main cause of vulvovaginal candidiasis (VVC); however, non-albicans Candida (NAC) species, such as Candida glabrata and Candida tropicalis, are now frequently identified in VVC patients. Although the vaginal microbiome (VMB) was well studied in Candida albicans-associated VVC patients, the fungal influence on bacterial communities of NAC species-associated VVC and potential microbial interplay contributing to VVC pathology remain elusive. We characterized VMB via Candida albicans and NAC species-associated VVC patients, as Candida albicans (CA, n = 16), Candida glabrata (CG, n = 16), Candida tropicalis (CT, n = 4), and recruiting healthy (CON, n = 20) women as references of dysbiosis and eubiosis. The bacterial diversity of the vagina in the CG group significantly declined. Further, all VVC patients have a higher abundance of Lactobacillus iners, especially for the CG group. Meanwhile, the predicted functions in all VVC are toned which may be associated with a disruption in the bacterial network. In conclusion, according to the taxonomic analysis, we found that the vaginal microbiome in C. glabrata-associated VVC women is different from that of other Candida species-associated VVC women, implying a different pathogenesis.

Distinct host immune responses in recurrent vulvovaginal candidiasis and vulvovaginal candidiasis

Recurrent vulvovaginal candidiasis (RVVC) and vulvovaginal candidiasis (RVVC) are one of the most common gynecological infections, primarily caused by Candida species. Although risk factors of RVVC and VVC have been identified in many studies, antifungal immunological mechanisms are still not fully understood. We performed a 1-year prospective study in a local hospital to monitor 98 patients clinically diagnosed with gynecological Candida infection. The results showed that 20.41% (20/98) are with RVVC, and 79.59% (78/98) patients have VVC. C. albicans accounts for 90% and 96.1% of all strains isolated collected from RVVC and VVC patients, respectively. Antifungal susceptibility testing showed no significant difference in Candida species between RVVC and VVC patients. However, the serum levels of IFN-γ, TNF-α, and IL-17F in the RVVC group were significantly lower than those of the VVC group, while IL-4, IL-6, and IL-10 were higher in the RVVC patients than VVC patients. IL-17A and IL-2 levels were comparable between the two groups. Taken together, our results suggest that the host-immune responses, especially Th1/2 immunity, may play important roles in prognosis of RVVC and VVC.

Elucidating the lactic acid tolerance mechanism in vaginal clinical isolates of Candida glabrata

Incidence of vulvovaginal candidiasis are strikingly high and treatment options are limited with nearly 50% Candida glabrata cases left untreated or experience treatment failures. The vaginal microenvironment is rich in lactic acid, and the adaptation of C. glabrata to lactic acid (LA) is the main reason for clinical treatment failure. In the present study, C. glabrata and its vaginal clinical isolates were comprehensively investigated for their growth response, metabolic adaptation and altered cellular pathway to LA using different biochemical techniques, metabolic profiling and transcriptional studies. C. glabrata shown considerable variations in its topological and biochemical features without compromising growth in LA media. Chemical profiling data highlighted involvement of cell wall/membrane, ergosterol and oxidative stress related pathways in mediating adaptative response of C. glabrata towards LA. Further, one dimensional proton (1H) NMR spectroscopy based metabolic profiling revealed significant modulation in 19 metabolites of C. glabrata cells upon growth in LA. Interestingly myo-inositol, xylose, putrescine and betaine which are key metabolites for cell growth and viability were found to be differentially expressed by clinical isolates. These observations were supported by the transcriptional expression study of selected genes evidencing cell wall/membrane re-organisation, altered oxidative stress, and reprogramming of carbon metabolic pathways. Collectively, the study advances our understanding on adaptative response of C. glabrata in vaginal microenvironment to lactic acid for survival and virulence.