Understanding recurrent vulvovaginal candidiasis as a dynamic biofilm disease of Candida and Lactobacillus

Additionally, women with RVVC using hormonal contraceptives were found to have a more similar bacterial profile to healthy women, compared with women using other contraceptives. C. albicans biofilm reduction by Lactobacillus species was observed in an in vitro co-culture model. Further, RNA sequencing revealed an α-amino acid biosynthesis/breakdown pathway by which L. crispatus may out-compete C. albicans during VVC to re-establish vaginal health. Finally, bi-daily addition of L. crispatus was shown to reduce C. albicans composition within a complex biofilm model. This study highlights the potential impact of Candida biofilm formation in RVVC and the importance of the consideration of biofilms for diagnosis and treatment. Additionally, it contributes to our current understanding of the vaginal microbiome during RVVC and antagonistic interactions between Candida and Lactobacillus. This work provides a foundation for future studies to further elucidate triggers for the development and recurrence of VVC/RVVC and the pathogenesis of the microbes involved. This and similar work will hopefully lead to the development of novel, more appropriate prevention and treatment options for persistent, azole resistant VVC. Additionally, women with RVVC using hormonal contraceptives were found to have a more similar bacterial profile to healthy women, compared with women using other contraceptives. C. albicans biofilm reduction by Lactobacillus species was observed in an in vitro co-culture model. Further, RNA sequencing revealed an α-amino acid biosynthesis/breakdown pathway by which L. crispatus may out-compete C. albicans during VVC to re-establish vaginal health. Finally, bi-daily addition of L. crispatus was shown to reduce C. albicans composition within a complex biofilm model. This study highlights the potential impact of Candida biofilm formation in RVVC and the importance of the consideration of biofilms for diagnosis and treatment. Additionally, it contributes to our current understanding of the vaginal microbiome during RVVC and antagonistic interactions between Candida and Lactobacillus. This work provides a foundation for future studies to further elucidate triggers for the development and recurrence of VVC/RVVC and the pathogenesis of the microbes involved. This and similar work will hopefully lead to the development of novel, more appropriate prevention and treatment options for persistent, azole resistant VVC

Candida albicans and Enterococcus faecalis biofilm frenemies: when the relationship sours

The opportunistic yeast Candida albicans and lactic acid bacteria Enterococcus faecalis are frequently co-isolated from various infection sites on the human body, suggesting a common interkingdom interaction. While some reports suggest an antagonism, the reason for their co-isolation therefore remains unclear. The purpose of this study was to undertake a detailed characterisation of this dual-species interaction. We used standard biofilm characterisation methodologies alongside an RNASeq analysis to assess the response of C. albicans to E. faecalis. We evaluated the relevance of pH to dual-species biofilm interactions and demonstrated that E. faecalis rapidly and significantly impacted C. albicans morphogenesis and biofilm formation, which was mirrored by levels of gene expression. These transcripts were enriched in amino acids biosynthesis and metabolism pathways in co-cultures, a finding that guided our investigation into pH related mechanism. We were able to demonstrate the direct role of E. faecalis induced low pH, which inhibited C. albicans hyphal morphogenesis and biofilm formation. The results suggest that the anti-candidal effect of E. faecalis is not based solely on a single mechanism, instead it may involve various mechanisms, which collectively reflects the complexity of interaction between C. albicans and E. faecalis and impacts treatment outcomes

Investigating the transcriptome of Candida albicans in a dual-species Staphylococcus aureus biofilm model

Candida albicans is an opportunistic pathogen found throughout multiple body sites and is frequently co-isolated from infections of the respiratory tract and oral cavity with Staphylococcus aureus. Herein we present the first report of the effects that S. aureus elicits on the C. albicans transcriptome. Dual-species biofilms containing S. aureus and C. albicans mutants defective in ALS3 or ECE1 were optimised and characterised, followed by transcriptional profiling of C. albicans by RNA-sequencing (RNA-seq). Altered phenotypes in C. albicans mutants revealed specific interaction profiles between fungus and bacteria. The major adhesion and virulence proteins Als3 and Ece1, respectively, were found to have substantial effects on the Candida transcriptome in early and mature biofilms. Despite this, deletion of ECE1 did not adversely affect biofilm formation or the ability of S. aureus to interact with C. albicans hyphae. Upregulated genes in dual-species biofilms corresponded to multiple gene ontology terms, including those attributed to virulence, biofilm formation and protein binding such as ACE2 and multiple heat-shock protein genes. This shows that S. aureus pushes C. albicans towards a more virulent genotype, helping us to understand the driving forces behind the increased severity of C. albicans-S. aureus infections

Chitosan ameliorates Candida auris virulence in a Galleria mellonella infection model

Candida auris has emerged as a multi-drug resistant nosocomial pathogen over the last decade. Outbreaks of the organism in healthcare facilities has resulted in life-threatening invasive candidiasis in over 40 countries worldwide. Resistance by C. auris to conventional antifungal drugs such as fluconazole and amphotericin B means that alternative therapeutics must be explored. As such, this study served to investigate the efficacy of a naturally derived polysaccharide called chitosan against aggregative (Agg) and non-aggregative (non-Agg) isolates of C. auris in vitro and in vivo. In vitro results indicated that chitosan was effective against planktonic and sessile forms of Agg and non-Agg C. auris. In a Galleria mellonella model to assess C. auris virulence, chitosan treatment was shown to ameliorate killing effects of both C. auris phenotypes (NCPF 8973 and NCPF 8978, respectively) in vivo. Specifically, chitosan reduced the fungal load and increased survival rates of infected Galleria, whilst treatment alone was non-toxic to the larvae. Finally, chitosan treatment appeared to induce a stress-like gene expression response in NCPF 8973 in the larvae likely arising from a protective response by the organism to resist antifungal activity of the compound. Taken together, results from this study demonstrate that naturally derived compounds such as chitosan may be useful alternatives to conventional antifungals against C. auris

Recurrent vulvovaginal candidiasis: a dynamic interkingdom biofilm disease of candida and lactobacillus

Despite the strikingly high worldwide prevalence of vulvovaginal candidiasis (VVC), treatment options for recurrent VVC (RVVC) remain limited, with many women experiencing failed clinical treatment with frontline azoles. Further, the cause of onset and recurrence of disease is largely unknown, with few studies identifying potential mechanisms of treatment failure. This study aimed to assess a panel of clinical samples from healthy women and those with RVVC to investigate the influence of Candida, the vaginal microbiome, and how their interaction influences disease pathology. 16S rRNA sequencing characterized disease by a reduction in specific health-associated Lactobacillus species, such as Lactobacillus crispatus, coupled with an increase in Lactobacillus iners. In vitro analysis showed that Candida albicans clinical isolates are capable of heterogeneous biofilm formation, and we found the presence of hyphae and C. albicans aggregates in vaginal lavage fluid. Additionally, the ability of Lactobacillus to inhibit C. albicans biofilm formation and biofilm-related gene expression was demonstrated. Using RNA sequencing technology, we were able to identify a possible mechanism by which L. crispatus may contribute to re-establishing a healthy vaginal environment through amino acid acquisition from C. albicans. This study highlights the potential formation and impact of Candida biofilms in RVVC. Additionally, it suggests that RVVC is not entirely due to an arbitrary switch in C. albicans from commensal to pathogen and that understanding interactions between this yeast and vaginal Lactobacillus species may be crucial to elucidating the cause of RVVC and developing appropriate therapies

An in vitro evaluation of denture cleansing regimens against a polymicrobial denture biofilm model

Denture stomatitis (DS) is an inflammatory disease resulting from a polymicrobial biofilm perturbation at the denture surface–palatal mucosa interface. Recommendations made by dental health care professionals often lack clarity for appropriate denture cleaning. This study investigated the efficacy of brushing with off-the-shelf denture cleanser (DC) tablets (Poligrip®) vs. two toothpastes (Colgate® and Crest®) in alleviating the viable microorganisms (bacteria and fungi) in an in vitro denture biofilm model. Biofilms were grown on poly(methyl)methacrylate (PMMA) discs, then treated daily for 7 days with mechanical disruption (brushing), plus Poligrip® DC, Colgate® or Crest® toothpastes. Weekly treatment with Poligrip® DC on day 7 only was compared to daily modalities. All treatment parameters were processed to determine viable colony forming units for bacteria and fungi using the Miles and Misra technique, and imaged by confocal laser scanning microscopy (CLSM). Brushing with daily DC therapy was the most effective treatment in reducing the viable biofilm over 7 days of treatment. Brushing only was ineffective in controlling the viable bioburden, which was confirmed by CLSM imaging. This data indicates that regular cleansing of PMMA with DC was best for polymicrobial biofilms

Biofilms formed by isolates from recurrent vulvovaginal candidiasis patients are heterogeneous and insensitive to fluconazole

Vulvovaginal candidiasis (VVC) is a global health problem affecting ∼75% of women at least once in their lifetime. Here we examined the epidemiology of VVC from a patient cohort to identify the causative organisms associated with VVC. Biofilm forming capacity and antifungal sensitivity profiles were also assessed. We report a shifting prevalence of Candida species with heterogeneous biofilm forming capacity, both of which are associated with altered antifungal drug sensitivity

Clinical management of fungal biofilm infections

Fungal biofilms are highly resilient to antifungal therapies, of which there are relatively few licensed options available in clinical medicine. Nonetheless, there is a vibrant research culture aimed at enhancing and expanding the arsenal of antifungals capable of inhibiting, killing, and disrupting fungal biofilms. This chapter aims to explore the wide variety of fungal biofilms affecting human health and to discuss the clinical options for existing and novel chemotherapeutics

The comparative efficacy of antiseptics against Candida auris biofilms

Candida auris has emerged as a significant clinical entity due to its ability to cause outbreaks within the healthcare setting. A key feature of its nosocomial lifestyle is its ability to transfer between patients, yet little is known about the mechanisms behind this. A panel of C. auris clinical isolates was screened for their planktonic and sessile susceptibilities to skin disinfection challenge using povidone iodine, chlorhexidine and hydrogen peroxide. C. auris biofilms displayed increased tolerance to these strategies compared to planktonic cells. Additionally, analysis using a complex biofilm model demonstrated reduced susceptibility against clinically relevant concentrations of chlorhexidine and hydrogen peroxide, with complete eradication achieved only using povidone iodine. Principal component analysis (PCA) also revealed distinct clustering of C. auris biofilms in comparison to C. albicans and C. glabrata biofilms, and directionality with respect to different treatments. These findings indicate differential responses of different Candida species with respect to antiseptic challenge against biofilms, with C. auris appearing to be more resilient as a complex community