Assessment of in vitro biofilm formation by Candida species isolates from vulvovaginal candidiasis and ultrastructural characteristics

Treatment of Vulvovaginal Candidiasis-An Overview of Guidelines and the Latest Treatment Methods

Vulvovaginal candidiasis (VVC) is a common condition associated with discomfort in affected women. Due to the presence of different forms of the disease, diverse treatment regimens are developed; the newest ones include oteseconazole and ibrexafungerp. Here, we focus on the most up-to-date recommendations regarding VVC treatment, as well as novel treatment options. Topical and oral azoles are the drugs of choice in uncomplicated mycosis. The efficacy of probiotics and substances such as TOL-463 and chlorhexidine is indicated as satisfactory; however, there are no relevant guidelines. Although the majority of researchers agree that the treatment of non-albicans VVC should be long-lasting, the recommendations are inconsistent. Another clinical problem is the treatment of VVC with azole intolerance or resistance, for which literature proposes the use of several drugs including oteseconazole, ibrexafungerp, and voriconazole. The treatment schedules for recurrent VVC include mainly fluconazole; however, alternative options such as immunotherapeutic vaccine (NDV-3A) or designed antimicrobial peptides (dAMPs) were also described. We also focused on VVC affecting pregnant women, which is a substantial challenge in clinical practice, also due to the heterogeneous relevant guidelines. Thus far, few precise recommendations are available in the literature. Future studies should focus on atypical VVC forms to elucidate the inconsistent findings.

Development of probiotic loaded multilayer microcapsules incorporated into dissolving microneedles for potential improvement treatment of vulvovaginal candidiasis: A proof of concept study

Vulvovaginal candidiasis (VVC) is a vaginal infection caused by abnormal growth of Candida sp., especially Candida albicans, in the vaginal mucosa. A shift in vaginal microbiota is prominent in VVC. The presence of Lactobacillus plays a vital role in maintaining vaginal health. However, several studies have reported resistance of Candida sp. against azoles drugs, which is recommended as VVC treatment. The use of L. plantarum as a probiotic would be an alternative to treat VVC. In order to exert their therapeutic activity, the probiotics needed to remain viable. Multilayer double emulsion was formulated to obtain L. plantarum loaded microcapsules (MCs), thus improving its viability. Furthermore, a vaginal drug delivery system using dissolving microneedles (DMNs) for VVC treatment was developed for the first time. These DMNs showed sufficient mechanical and insertion properties, dissolved rapidly upon insertion, facilitating probiotic release. All formulations proved non-irritating, non-toxic, and safe to apply on the vaginal mucosa. Essentially, the DMNs could inhibit the growth of Candida albicans up to 3-fold than hydrogel and patch dosage forms in ex vivo infection model. Therefore, this study successfully developed the formulation of L. plantarum-loaded MCs with multilayer double emulsion and its combination in DMNs for vaginal delivery to treat VVC.

Candida albicans antibiofilm molecules: analysis based on inhibition and eradication studies

Biofilms are communities of microbial cells surrounded by an extracellular polysaccharide matrix, recognized as a fungal source for local and systemic infections and less susceptible to antifungal drugs. Thus, treatment of biofilm-related Candida spp. infections with popular antifungals such as fluconazole is limited and species-dependent and alternatively demands the use of expensive and high toxic drugs. In this sense, molecules with antibiofilm activity have been studied but without care regarding the use of important criteria such as antibiofilm concentration lower than antifungal concentration when considering the process of inhibition of formation and concentrations equal to or lower than 300 µM. Therefore, this review tries to gather the most promising molecules regarding the activity against the C. albicans biofilm described in the last 10 years, considering the activity of inhibition and eradication. From January 2011 to July 2021, articles were searched on Scopus, PubMed, and Science Direct, combining the keywords "antibiofilm," "candida albicans," "compound," and "molecule" with AND and OR operators. After 3 phases of selection, 21 articles describing 42 molecules were discussed in the review. Most of them were more promising for the inhibition of biofilm formation, with SM21 (24) being an interesting molecule for presenting inhibitory and eradication activity in biofilms with 24 and 48 h, as well as alizarin (26) and chrysazine (27), with concentrations well below the antifungal concentration. Despite the detection of these molecules and the attempts to determine the mechanisms of action by microscopic analysis and gene expression, no specific target has been determined. Thus, a gap is signaled, requiring further studies such as proteomic analyses to clarify it.

Virulence Factors of Candida spp. and Host Immune Response Important in the Pathogenesis of Vulvovaginal Candidiasis

Vulvovaginal candidiasis (VVC) is one of the most common types of vaginal infections in women around the world and is often underestimated by both patients and doctors. Research on the pathogenesis of fungal vaginal infections over the last 20 years has resulted in a closer understanding of the virulence factors involved in Candida epithelial invasion and their mechanisms of action. Recently, attention was drawn to the enormous complexity of the interaction between yeast-like fungi and host cells, as well as the level of complexity of the host's response to infection and their impact on the course and treatment of VVC. Our work provides a broad description of already known and some new reports on Candida virulence factors (such as phenotypic switching or biofilm formation capacity) and their importance for tissue invasion in VVC. At the same time, we also focus on interactions with host cells and local innate immune mechanisms involved in the response to vaginal fungal invasion that are now considered equally important in this case. The presented review describes the most important aspects of the still unknown pathogenicity of Candida associated with vaginal infections.

Spilanthol as a promising antifungal alkylamide for the treatment of vulvovaginal candidiasis

Spilanthol is a bioactive alkylamide from the native Amazon plant species, Acmella oleracea. However, antifungal activities of spilanthol and its application to the therapeutic treatment of candidiasis remain to be explored. This study sought to evaluate the in vitro and in vivo antifungal activity of spilanthol previously isolated from A. oleracea (spilanthol(AcO)) against Candida albicans ATCC® 10231™, a multidrug-resistant fungal strain. Microdilution methods were used to determine inhibitory and fungicidal concentrations of spilanthol(AcO). In planktonic cultures, the fungal growth kinetics, yeast cell metabolic activity, cell membrane permeability and cell wall integrity were investigated. The effect of spilanthol(AcO) on the proliferation and adhesion of fungal biofilms was evaluated by whole slide imaging and scanning electron microscopy. The biochemical composition of the biofilm matrix was also analyzed. In parallel, spilanthol(AcO) was tested in vivo in an experimental vulvovaginal candidiasis model. Our in vitro analyses in C. albicans planktonic cultures detected a significant inhibitory effect of spilanthol(AcO), which affects both yeast cell membrane and cell wall integrity, interfering with the fungus growth. C. albicans biofilm proliferation and adhesion, as well as, carbohydrates and DNA in biofilm matrix were reduced after spilanthol(AcO) treatment. Moreover, infected rats treated with spilanthol(AcO) showed consistent reduction of both fungal burden and inflammatory processes compared to the untreated animals. Altogether, our findings demonstrated that spilanthol(AcO) is an bioactive compound against planktonic and biofilm forms of a multidrug resistant C. albicans strain. Furthermore, spilanthol(AcO) can be potentially considered for therapeutical treatment of vulvovaginal candidiasis caused by C. albicans.

LAY SUMMARY

This study sought to evaluate the antifungal activity of spilanthol against Candida albicans ATCC® 10 231™, a multidrug-resistant fungal strain. Our findings demonstrated that spilanthol(AcO) can be potentially considered for therapeutical treatment of vulvovaginal candidiasis caused by C. albicans.

Insights into the activation of oral keratinocyte cell death by Candida albicans and Staphylococcus aureus biofilms

Polymicrobial biofilms comprising Candida albicans and Staphylococcus aureus can increase the frequency and severity of oral diseases. This study assessed oral keratinocyte cell death, apoptosis and/or necrosis, promoted by soluble factors from single and dual biofilms of S. aureus and C. albicans. The soluble factors were obtained from the 16-h biofilm growth media. Cell viability was assessed by MTT and cell membrane damage by LDH. SEM was used for morphology changes. Assessment of apoptosis and necrosis was performed using annexin V and propidium iodide and caspases -2, -3, -6, -8 and -9. Statistical analysis was conducted with ANOVA and Tukey tests (α = 5%). Dual biofilms promoted the greatest harmful effect on oral cells, with a viability rate of 31.76%, damage to cell membranes and LDH released. Dual biofilms also induced higher percentages of necrotic cells (24.95%). Apoptosis was associated with caspases -2, -3, -6 and -8 activation.

Antifungal Activity of Linear and Disulfide-Cyclized Ultrashort Cationic Lipopeptides Alone and in Combination with Fluconazole against Vulvovaginal Candida spp

Vulvovaginal candidiasis (VVC) occurs in over 75% of women at least once during their lifetime and is an infection that significantly affects their health. Candida strains resistant to standard azole antifungal therapy and relapses of VVC are more and more common. Hypothetically, biofilm is one of the main reasons of relapses and failure of the therapy. Ultrashort cationic lipopeptides (USCLs) exhibit high antimicrobial activities. Our previous study on USCLs revealed that disulfide cyclization can result in selective antifungal compounds. Therefore, four USCL were selected and their antifungal activity were studied on 62 clinical strains isolated from VVC. The results confirmed previous premises that cyclic analogs have increased selectivity between fungal cells and keratinocytes and improved anticandidal activity compared to their linear analogs against both planktonic and biofilm cultures. On the other hand, linear lipopeptides in combination with fluconazole showed a synergistic effect. It was found that the minimum inhibitory concentrations of the tested compounds in combination with fluconazole were at least four times lower than when used separately. Our results indicate that combination therapy of VVC with USCLs and fluconazole at low non-toxic concentrations can be beneficial owing to the synergistic effect. However, further in vivo studies are needed to confirm this hypothesis.

Treating (Recurrent) Vulvovaginal Candidiasis with Medical-Grade Honey-Concepts and Practical Considerations

Recurrent vulvovaginal candidiasis (RVVC) is a relapsing vaginal fungal infection caused by Candida species. The prevalence varies among age populations and can be as high as 9%. Treatment options are limited, and in 57% of the cases, relapses occur within six months after fluconazole maintenance therapy, which is the current standard of care. The pathogenesis of RVVC is multifactorial, and recent studies have demonstrated that the vaginal microenvironment and activity of the immune system have a strong influence on the disease. Medical-grade honey (MGH) has protective, antimicrobial, and immunomodulatory activity and forms a putative alternative treatment. Clinical trials have demonstrated that honey can benefit the treatment of bacterial and Candida-mediated vaginal infections. We postulate that MGH will actively fight ongoing infections; eradicate biofilms; and modulate the vaginal microenvironment by its anti-inflammatory, antioxidative, and immunomodulatory properties, and subsequently may decrease the number of relapses when compared to fluconazole. The MGH formulation L-Mesitran Soft has stronger antimicrobial activity against various Candida species than its raw honey. In advance of a planned randomized controlled clinical trial, we present the setup of a study comparing L-Mesitran Soft with fluconazole and its practical considerations.

Anticandidal Activity of Omiganan and Its Retro Analog Alone and in Combination with Fluconazole

Vulvovaginal candidiasis (VVC) is a vaginal infection that manifests itself as several symptoms which can lead to various life-threatening complications. The majority of VVC is caused by Candida albicans strains, and it is estimated that approximately 75% of women worldwide would suffer from this condition at least once during their lifetime. Surprisingly, the detailed pathomechanism of yeast-like fungi invasions in vagina is not yet fully understood. However, the ability to form biofilm on vaginal mucosa is considered as one of the critical factors associated with failure of the therapy and recurrences of the disease. Antimicrobial peptides (AMPs) are a promising class of compounds that are receiving a growing interest owing to their antibacterial, antifungal, and antibiofilm properties. Omiganan is a synthetic analog of Indolicidin that is characterized by wide spectrum of antimicrobial and antibiofilm activities. Recent reports suggest improved activity of analogs with a reversed sequence (retro-analog concept). Therefore, Omiganan and its retro analog were tested against planktonic forms and biofilm of 18 Candida strains isolated from VVC. Moreover, the synergy between the AMPs and fluconazole was studied as well. The AMPs appeared to be effective against C. albicans biofilm, and the reversion of the sequence generally led to an improved antimicrobial activity. Furthermore, confocal and scanning electron microscopic visualizations revealed the effectiveness of AMPs-fluconazole combinations also against fluconazole-resistant strains.

Whole slide imaging is a high-throughput method to assess Candida biofilm formation

New strategies that enable fast and accurate visualization of Candida biofilms are necessary to better study their structure and response to antifungals agents. Here, we applied whole slide imaging (WSI) to study biofilm formation of Candida species. Three relevant biofilm-forming Candida species (C. albicans ATCC 10231, C. glabrata ATCC 2001, and C. tropicalis ATCC 750) were cultivated on glass coverslips both in presence and absence of widely used antifungals. Accumulated biofilms were stained with fluorescent markers and scanned in both bright-field and fluorescence modes using a WSI digital scanner. WSI enabled clear assessment of both size and structural features of Candida biofilms. Quantitative analyses readily detected reductions in biofilm-covered surface area upon antifungal exposure. Furthermore, we show that the overall biofilm growth can be adequately assessed across both bright-field and fluorescence modes. At the single-cell level, WSI proved adequate, as morphometric parameters evaluated with WSI did not differ significantly from those obtained with scanning electron microscopy, considered as golden standard at single-cell resolution. Thus, WSI allows for reliable visualization of Candida biofilms enabling both large-scale growth assessment and morphometric characterization of single-cell features, making it an important addition to the available microscopic toolset to image and analyse fungal biofilm growth.

Candida albicans biofilms and polymicrobial interactions

Candida albicans is a common fungus of the human microbiota. While generally a harmless commensal in healthy individuals, several factors can lead to its overgrowth and cause a range of complications within the host, from localized superficial infections to systemic life-threatening disseminated candidiasis. A major virulence factor of C. albicans is its ability to form biofilms, a closely packed community of cells that can grow on both abiotic and biotic substrates, including implanted medical devices and mucosal surfaces. These biofilms are extremely hard to eradicate, are resistant to conventional antifungal treatment and are associated with high morbidity and mortality rates, making biofilm-associated infections a major clinical challenge. Here, we review the current knowledge of the processes involved in C. albicans biofilm formation and development, including the central processes of adhesion, extracellular matrix production and the transcriptional network that regulates biofilm development. We also consider the advantages of the biofilm lifestyle and explore polymicrobial interactions within multispecies biofilms that are formed by C. albicans and selected microbial species.

Vulvovaginal Candidosis: Current Concepts, Challenges and Perspectives

Vulvovaginal candidosis (VVC) is a frequently occurring infection of the lower female genital tract, mostly affecting immuno-competent women at childbearing age. Candida albicans is the most prevalent pathogenic yeast—apart from other non-albicans species—related to this fungal infection. Different virulence factors of C. albicans have been identified, which increase the risk of developing VVC. To initiate treatment and positively influence the disease course, fast and reliable diagnosis is crucial. In this narrative review, we cover the existing state of understanding of the epidemiology, pathogenesis and diagnosis of VVC. However, treatment recommendations should follow current guidelines.

Biofilm formation of Candida Spp. isolated from the vagina and antibiofilm activities of lactic acid bacteria on the these Candida Isolates

Background

In this study, it was aimed to investigate the effects of bacterial cells and cell-free filtrates of Lactobacillus acidophilus 8MR7 and Lactobacillus paracasei subspecies paracasei 10MR8 on the biofilm formation of 3 Candida tropicalis, 3 C. glabrata and 12 C. albicans isolated from the vagina and identified their virulence factors.

Methods

Haemolytic activities esterase activities, and phospholipase activities as virulence factors of Candida strains were determined. Biofilm formations of these isolates were determined by Congo Red agar and microtitration plate method. Antibiofilm activities of bacterial cells and cell-free filtrates of L. acidophilus 8MR7 and L. paracasei subspecies paracasei 10MR8 on Candida isolates were determined by the microtitration plate method.

Result

Bacterial cells of L. acidophilus 8MR7 and L. paracasei subspecies paracasei 10MR8 were not very effective in the inhibition of biofilm, whereas it has been observed that the cell-free filtrates of these bacteria inhibit the formation of biofilms of Candida strains. Although the main mechanism for inhibiting the formation of Candida spp. biofilm is the competition for adhesion, it is concluded that the substances contained in the cell-free filtrates of lactic acid bacteria are also important.

Conclusion

These isolates promise hope as potential bacteria that can be used for anti-adhesion purposes in health-care materials.

Microbiota in vaginal health and pathogenesis of recurrent vulvovaginal infections: a critical review

Recurrent vulvovaginal infections (RVVI) has not only become an epidemiological and clinical problem but also include large social and psychological consequences. Understanding the mechanisms of both commensalism and pathogenesis are necessary for the development of efficient diagnosis and treatment strategies for these enigmatic vaginal infections. Through this review, an attempt has been made to analyze vaginal microbiota (VMB) from scratch and to provide an update on its current understanding in relation to health and common RVVI i.e. bacterial vaginosis, vulvovaginal candidiaisis and Trichomoniasis, making the present review first of its kind. For this, potentially relevant studies were retrieved from data sources and critical analysis of the literature was made. Though, culture-independent methods have greatly unfolded the mystery regarding vaginal bacterial microbiome, there are only a few studies regarding the composition and diversity of vaginal mycobiome and different Trichomonas vaginalis strains. This scenario suggests a need of further studies based on comparative genomics of RVVI pathogens to improve our perceptive of RVVI pathogenesis that is still not clear (Fig. 5). Besides this, the review details the rationale for Lactobacilli dominance and changes that occur in healthy VMB throughout a women's life. Moreover, the list of possible agents continues to expand and new species recognised in both health and VVI are updated in this review. The review concludes with the controversies challenging the widely accepted dogma i.e. "VMB dominated with Lactobacilli is healthier than a diverse VMB". These controversies, over the past decade, have complicated the definition of vaginal health and vaginal infections with no definite conclusion. Thus, further studies on newly recognised microbial agents may reveal answers to these controversies. Conversely, VMB of women could be an answer but it is not enough to just look at the microbiology. We have to look at the woman itself, as VMB which is fine for one woman may be troublesome for others. These differences in women's response to the same VMB may be determined by a permutation of behavioural, cultural, genetic and various other anonymous factors, exploration of which may lead to proper definition of vaginal health and disease.

Impaired Th17 cell proliferation and decreased pro-inflammatory cytokine production in CXCR3/CXCR4 double-deficient mice of vulvovaginal candidiasis

Vulvovaginal candidiasis (VVC) is a common observed infection, affecting approximately 75% of women of reproductive age. Drug resistance represents a troublesome stumbling block associated with VVC therapy. Thus the aim of the present study was to provide information regarding the selection of potential drug targets for VVC. CXCR3-, CXCR4-, or CXCR/CXCR4 double-deficient mouse models of VVC were subsequently established, with changes to the load of Candida Albicans evaluated accordingly. The biological behaviors of the vaginal epithelial cells were characterized in response to the CXCR3-, CXCR4-, or CXCR3/CXCR4 double-knockout in vivo. Our initial observations revealed that in mice with VVC, CXCR3-, CXCR4-, or CXCR3 - CXCR4 double-knockout resulted in a decreased load of C. Albicans as well as reduced levels and proportion of Th17 cells. Proinflammatory cytokine production was found to be inhibited by CXCR3-, CXCR4-, or CXCR3/CXCR4 double-knockout whereby the mRNA and protein expressions CXCR3, CXCR4, IL-17, IL-6, and TNF-α exhibited decreased levels. CXCR3-, CXCR4-, or CXCR3/CXCR4 double-knockout appeared to function as positive proliferation factors, while playing a negative role in the processes of apoptosis and the cell cycle of vaginal epithelial cells. Taken together, the key findings of the study suggested that CXCR3/CXCR4 double-knockout could act to hinder the progression of VVC, highlighting its promise as a novel therapeutic target in the treatment of VVC. CXCR3 and CXCR4 genes may regulate Th17/IL-17 immune inflammatory pathways to participate in antifungal immunity.

A study on biofilm production and antifungal drug resistance among Candida species from vulvovaginal and bloodstream infections

Introduction

Candida species, one among the opportunistic fungi, has become a common pathogen causing vaginal thrush and nosocomial bloodstream infections (BSIs). This study aims to evaluate the prevalence and antifungal susceptibility of various Candida species and slime production by Candida species in BSIs and vulvovaginal candidiasis (VVC).

Materials and methods

A total of 176 samples were collected for a period of 1 year. Anti-fungal susceptibility testing and biofilm production testing were performed by the Kirby-Bauer method and crystal violet assay, respectively.

Results

Out of 176 samples, 74 (42%) were from BSIs and 102 (58%) were from VVC. The biofilm production was comparatively high in blood isolates, 55 (74%), than cervical isolates, 45 (44%). Increase in the trends of non-albicans Candida (NAC) species was seen in our setup. Good susceptibility rates were seen among Candida species, 82.38% to voriconazole and an increasing resistance pattern of 26.13% to fluconazole.

Conclusion

Speciation of Candida becomes important as the prevalence of NAC is increasing. Antifungal susceptibility testing by the disk diffusion method is cost effective and should be adopted in routine testing as there is an increasing azole resistance, especially in invasive NAC infections. In this study, there was no correlation of antifungal drugs with the biofilm production.

Monitoring Candida parapsilosis and Staphylococcus epidermidis Biofilms by a Combination of Scanning Electron Microscopy and Raman Spectroscopy

The biofilm-forming microbial species Candida parapsilosis and Staphylococcus epidermidis have been recently linked to serious infections associated with implanted medical devices. We studied microbial biofilms by high resolution scanning electron microscopy (SEM), which allowed us to visualize the biofilm structure, including the distribution of cells inside the extracellular matrix and the areas of surface adhesion. We compared classical SEM (chemically fixed samples) with cryogenic SEM, which employs physical sample preparation based on plunging the sample into various liquid cryogens, as well as high-pressure freezing (HPF). For imaging the biofilm interior, we applied the freeze-fracture technique. In this study, we show that the different means of sample preparation have a fundamental influence on the observed biofilm structure. We complemented the SEM observations with Raman spectroscopic analysis, which allowed us to assess the time-dependent chemical composition changes of the biofilm in vivo. We identified the individual spectral peaks of the biomolecules present in the biofilm and we employed principal component analysis (PCA) to follow the temporal development of the chemical composition.

Biofilms and vulvovaginal candidiasis

Candida species, including C. albicans, are part of the mucosal flora of most healthy women, and inhabit the gastrointestinal and genitourinary tracts. Under favourable conditions, they can colonize the vulvovaginal mucosa, giving rise to symptomatic vulvovaginal candidiasis (VVC). The mechanism by which Candida spp. produces inflammation is unknown. Both, the blastoconidia and the pseudohyphae are capable of destroying the vaginal epithelium by direct invasion. Although the symptoms are not always related to the fungal burden, in general, VVC is associated with a greater number of yeasts and pseudohyphae. Some years ago, C. albicans was the species most frequently involved in the different forms of VVC. However, infections by different species have emerged during the last two decades producing an increase in causative species of VVC such as C. glabrata, C. parapsilosis, C. krusei and C. tropicalis. Candida species are pathogenic organisms that have two forms of development: planktonic and biofilm. A biofilm is defined as a community of microorganisms attached to a surface and encompassed by an extracellular matrix. This form of presentation gives microorganisms greater resistance to antifungal agents. This review, about Candia spp. with a special emphasis on Candida albicans discusses specific areas such as biofilm structure and development, cell morphology and biofilm formation, biofilm-associated gene expression, the cell surface and adherence, the extracellular matrix, biofilm metabolism, and biofilm drug resistance in vulvovaginitis biofilms as an important virulence factor in fungi.

The innovation of cryo-SEM freeze-fracturing methodology demonstrated on high pressure frozen biofilm

In this study we present an innovative method for the preparation of fully hydrated samples of microbial biofilms of cultures Staphylococcus epidermidis, Candida parapsilosis and Candida albicans. Cryo-scanning electron microscopy (cryo-SEM) and high-pressure freezing (HPF) rank among cutting edge techniques in the electron microscopy of hydrated samples such as biofilms. However, the combination of these techniques is not always easily applicable. Therefore, we present a method of combining high-pressure freezing using EM PACT2 (Leica Microsystems), which fixes hydrated samples on small sapphire discs, with a high resolution SEM equipped with the widely used cryo-preparation system ALTO 2500 (Gatan). Using a holder developed in house, a freeze-fracturing technique was applied to image and investigate microbial cultures cultivated on the sapphire discs. In our experiments, we focused on the ultrastructure of the extracellular matrix produced during cultivation and the relationships among microbial cells in the biofilm. The main goal of our investigations was the detailed visualization of areas of the biofilm where the microbial cells adhere to the substrate/surface. We show the feasibility of this technique, which is clearly demonstrated in experiments with various freeze-etching times.

An Update on Candida tropicalis Based on Basic and Clinical Approaches

Candida tropicalis has emerged as one of the most important Candida species. It has been widely considered the second most virulent Candida species, only preceded by C. albicans. Besides, this species has been recognized as a very strong biofilm producer, surpassing C. albicans in most of the studies. In addition, it produces a wide range of other virulence factors, including: adhesion to buccal epithelial and endothelial cells; the secretion of lytic enzymes, such as proteinases, phospholipases, and hemolysins, bud-to-hyphae transition (also called morphogenesis) and the phenomenon called phenotypic switching. This is a species very closely related to C. albicans and has been easily identified with both phenotypic and molecular methods. In addition, no cryptic sibling species were yet described in the literature, what is contradictory to some other medically important Candida species. C. tropicalis is a clinically relevant species and may be the second or third etiological agent of candidemia, specifically in Latin American countries and Asia. Antifungal resistance to the azoles, polyenes, and echinocandins has already been described. Apart from all these characteristics, C. tropicalis has been considered an osmotolerant microorganism and this ability to survive to high salt concentration may be important for fungal persistence in saline environments. This physiological characteristic makes this species suitable for use in biotechnology processes. Here we describe an update of C. tropicalis, focusing on all these previously mentioned subjects.

Candida and its dual lifestyle as a commensal and a pathogen

Candida spp. are part of the normal vaginal microflora in 20-30% of healthy women. However, if the balance between these yeasts and the host is disturbed, Candida spp. can cause vulvovaginal candidiasis (VVC), with Candida albicans being the major causative agent. Different studies have been performed in order to better understand Candida's dual lifestyle in the vagina. The potential of C. albicans to switch from the yeast cell morphology to its hyphal form is considered a key element in VVC pathogenesis. Candida spp. also express other virulence factors, such as hydrolytic extracellular enzymes and heat shock proteins and can form biofilms.

Identification, antifungal resistance profile, in vitro biofilm formation and ultrastructural characteristics of Candida species isolated from diabetic foot patients in Northern India

PURPOSE

Diabetic foot ulcers are a serious cause of diagnostic and therapeutic concern. The following study was undertaken to determine the fungal causes of diabetic foot ulcers, with their phenotypic and genotypic characterisation.

MATERIALS AND METHODS

A total of 155 diabetic foot ulcers were studied for 1 year. Deep tissue specimen was collected from the wounds, and crushed samples were plated on Sabouraud dextrose agar with chloramphenicol (0.05 g). Identification was done by growth on cornmeal agar, germ tube formation and urease test. For molecular identification, conserved portion of the 18S rDNA region, the adjacent internal transcribed spacer 1 (ITS1) and a portion of the 28S rDNA region were amplified, using the ITS1 and ITS2 primers. Antifungal susceptibility against voriconazole, fluconazole and amphotericin B was determined by standard broth microdilution method. Biofilm formation was studied in three steps. First, on the surface of wells of microtiter plates followed by quantification of growth by fungal metabolism measurement. Finally, biofilms were analysed by scanning electron microscopy (SEM).

RESULTS

Fungal aetiology was found in 75 patients (48.38%). All were identified as Candida species (100%). The prevalence of different species was Candida tropicalis (34.6%), Candida albicans (29.3%), Candida krusei (16.0%), Candida parapsilosis (10.6%), Candida glabrata (9.33%). All were susceptible to amphotericin B (100%). On microtiter plate, all the isolates were viable within 48 h showing biofilms. The metabolic activity of cells in the biofilm increased with cellular mass, especially in the first 24 h. On SEM, majority showed budding yeast form.

CONCLUSION

Non-albicans Candida spp. with potential biofilm forming ability are emerging as a predominant cause of diabetic foot ulcers.

Evaluation of Virulence Factors In vitro, Resistance to Osmotic Stress and Antifungal Susceptibility of Candida tropicalis Isolated from the Coastal Environment of Northeast Brazil

Several studies have been developed regarding human health risks associated with the recreational use of beaches contaminated with domestic sewage. These wastes contain various micro-organisms, including Candida tropicalis. In this context, the objective of this study was to characterize C. tropicalis isolates from the sandy beach of Ponta Negra, Natal, Rio Grande do Norte, Brazil, regarding the expression of in vitro virulence factors, adaptation to osmotic stress and susceptibility to antifungal drugs. We analyzed 62 environmental isolates and observed a great variation among them for the various virulence factors evaluated. In general, environmental isolates were more adherent to human buccal epithelial cells (HBEC) than C. tropicalis ATCC13803 reference strain, and they also showed increased biofilm production. Most of the isolates presented wrinkled phenotypes on Spider medium (34 isolates, 54.8%). The majority of the isolates also showed higher proteinase production than control strains, but low phospholipase activity. In addition, 35 isolates (56.4%) had high hemolytic activity (hemolysis index > 0.55). With regard to C. tropicalis resistance to osmotic stress, 85.4% of the isolates were able to grow in a liquid medium containing 15% sodium chloride. The strains were highly resistant to the azoles tested (fluconazole, voriconazole and itraconazole). Fifteen strains were resistant to the three azoles tested (24.2%). Some strains were also resistant to amphotericin B (14 isolates; 22.6%), while all of them were susceptible for the echinocandins tested, except for a single strain of intermediate susceptibility to micafungin. Our results demonstrate that C. tropicalis isolated from the sand can fully express virulence attributes and showed a high persistence capacity on the coastal environment; in addition of showing high minimal inhibitory concentrations to several antifungal drugs used in current clinical practice, demonstrating that environmental isolates may have pathogenic potential.

The vaginal mycobiome: A contemporary perspective on fungi in women's health and diseases

Most of what is known about fungi in the human vagina has come from culture-based studies and phenotypic characterization of single organisms. Though valuable, these approaches have masked the complexity of fungal communities within the vagina. The vaginal mycobiome has become an emerging field of study as genomics tools are increasingly employed and we begin to appreciate the role these fungal communities play in human health and disease. Though vastly outnumbered by its bacterial counterparts, fungi are important constituents of the vaginal ecosystem in many healthy women. Candida albicans, an opportunistic fungal pathogen, colonizes 20% of women without causing any overt symptoms, yet it is one of the leading causes of infectious vaginitis. Understanding its mechanisms of commensalism and patho-genesis are both essential to developing more effective therapies. Describing the interactions between Candida, bacteria (such as Lactobacillus spp.) and other fungi in the vagina is funda-mental to our characterization of the vaginal mycobiome.

Antifungal activity of cathelicidin peptides against planktonic and biofilm cultures of Candida species isolated from vaginal infections

Vulvovaginal candidiasis (VVC) is a frequent gynecological condition caused by Candida albicans and a few non-albicans Candida spp. It has a significant impact on the quality of life of the affected women also due to a considerable incidence of recurrent infections that are difficult to treat. The formation of fungal biofilm may contribute to the problematic management of recurrent VVC due to the intrinsic resistance of sessile cells to the currently available antifungals. Thus, alternative approaches for the prevention and control of biofilm-related infections are urgently needed. In this regard, the cationic antimicrobial peptides (AMPs) of the innate immunity are potential candidates for the development of novel antimicrobials as many of them display activity against biofilm formed by various microbial species. In the present study, we investigated the in vitro antifungal activities of the cathelicidin peptides LL-37 and BMAP-28 against pathogenic Candida spp. also including C. albicans, isolated from vaginal infections, and against C. albicans SC5314 as a reference strain. The antimicrobial activity was evaluated against planktonic and biofilm-grown Candida cells by using microdilution susceptibility and XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assays and, in the case of established biofilms, also by CFU enumeration and fluorescence microscopy. BMAP-28 was effective against planktonically grown yeasts in standard medium (MIC range, 2-32μM), and against isolates of C. albicans and Candida krusei in synthetic vaginal simulated fluid (MIC range 8-32μM, depending on the pH of the medium). Established 48-h old biofilms formed by C. albicans SC5314 and C. albicans and C. krusei isolates were 70-90% inhibited within 24h incubation with 16μM BMAP-28. As shown by propidium dye uptake and CFU enumeration, BMAP-28 at 32μM killed sessile C. albicans SC5314 by membrane permeabilization with a faster killing kinetics compared to 32μM miconazole (80-85% reduced biofilm viability in 90min vs 48h). In addition, BMAP-28 at 16μM prevented Candida biofilm formation on polystyrene and medical grade silicone surfaces by causing a >90% reduction in the viability of planktonic cells in 30min. LL-37 was overall less effective than BMAP-28 against planktonic Candida spp. (MIC range 4-≥64μM), and was ineffective against established Candida biofilms. However, LL-37 at 64μM prevented Candida biofilm development by inhibiting cell adhesion to polystyrene and silicone surfaces. Finally, Candida adhesion was strongly inhibited when silicone was pre-coated with a layer of BMAP-28 or LL-37, encouraging further studies for the development of peptide-based antimicrobial coatings.

Biofilms: An Underappreciated Mechanism of Treatment Failure and Recurrence in Vaginal Infections

Biofilms are microbial communities of surface-attached cells embedded in a self-produced extracellular matrix. They are of major medical significance because they decrease susceptibility to antimicrobial agents and enhance the spread of antimicrobial resistance. Biofilm-associated bacterial and fungal microorganisms have increasingly been recognized to play a role in multiple infectious diseases, particularly in their persistence and recurrence. More recently, biofilms have also been implicated in vaginal infections, notably bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC), particularly in the setting of treatment failure and recurrence. The purpose of this review is to discuss the impact of biofilms on the management and treatment of BV and recurrent VVC and highlight the need for additional research and development of novel therapeutics targeting pathogenic vaginal biofilms.

Identification of novel mechanisms involved in generating localized vulvodynia pain

OBJECTIVE

Our goal was to gain a better understanding of the inflammatory pathways affected during localized vulvodynia, a poorly understood, common, and debilitating condition characterized by chronic pain of the vulvar vestibule.

STUDY DESIGN

In a control matched study, primary human fibroblast strains were generated from biopsies collected from localized provoked vulvodynia (LPV) cases and from age- and race-matched controls. We then examined intracellular mechanisms by which these fibroblasts recognize pathogenic Candida albicans; >70% of vulvodynia patients report the occurrence of prior chronic Candida infections, which is accompanied by localized inflammation and elevated production of proinflammatory/pain-associated interleukin (IL)-6 and prostaglandin E2 (PGE2). We focused on examining the signaling pathways involved in recognition of yeast components that are present and abundant during chronic infection.

RESULTS

Dectin-1, a surface receptor that binds C albicans cell wall glucan, was significantly elevated in vestibular vs external vulvar cells (from areas without pain) in both cases and controls, while its abundance was highest in LPV cases. Blocking Dectin-1 signaling significantly reduced pain-associated IL-6 and PGE2 production during the response to C albicans. Furthermore, LPV patient vestibular cells produced inflammatory mediators in response to low numbers of C albicans cells, while external vulvar fibroblasts were nonresponsive. Inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (proinflammatory transcription factor) nearly abrogated IL-6 and PGE2 production induced by C albicans, in keeping with observations that Dectin-1 signals through the nuclear factor kappa-light-chain-enhancer of activated B cells pathway.

CONCLUSION

These findings implicate that a fibroblast-mediated proinflammatory response to C albicans contributes to the induction of pain in LPV cases. Targeting this response may be an ideal strategy for the development of new vulvodynia therapies.

Diverse nitrogen sources in seminal fluid act in synergy to induce filamentous growth of Candida albicans

The pathogenic fungus Candida albicans is the leading cause of vulvovaginal candidiasis (VVC). VVC represents a major quality-of-life issue for women during their reproductive years, a stage of life where the vaginal epithelium is subject to periodic hormonally induced changes associated with menstruation and concomitant exposure to serum as well as potential intermittent contact with seminal fluid. Seminal fluid potently triggers Candida albicans to switch from yeastlike to filamentous modes of growth, a developmental response tightly linked to virulence. Conversely, vaginal fluid inhibits filamentation. Here, we used artificial formulations of seminal and vaginal fluids that faithfully mimic genuine fluids to assess the contribution of individual components within these fluids to filamentation. The high levels of albumin, amino acids, and N-acetylglucosamine in seminal fluid act synergistically as potent inducers of filamentous growth, even at atmospheric levels of CO2 and reduced temperatures (30 °C). Using a simplified in vitro model that mimics the natural introduction of seminal fluid into the vulvovaginal environment, a pulse of artificial seminal fluid (ASF) was found to exert an enduring potential to overcome the inhibitory efficacy of artificial vaginal fluid (AVF) on filamentation. These findings suggest that a transient but substantial change in the nutrient levels within the vulvovaginal environment during unprotected coitus can induce resident C. albicans cells to engage developmental programs associated with virulent growth.

Biofilm formation by clinical isolates and its relevance to clinical infections

Reports of biofilms have increased exponentially in the scientific literature over the past two decades, yet the vast majority of these are basic science investigations with limited clinical relevance. Biofilm studies involving clinical isolates are most often surveys of isolate collections, but suffer from lack of standardization in methodologies for producing and assessing biofilms. In contrast, more informative clinical studies correlating biofilm formation to patient data have infrequently been reported. In this chapter, biofilm surveys of clinical isolates of aerobic and anaerobic bacteria, mycobacteria, and Candida are reviewed, as well as those pertaining to the unique situation of cystic fibrosis. In addition, the influence of host components on in vitro biofilm formation, as well as published studies documenting the clinical impact of biofilms in human infections, are presented.

Biofilm Formation and Susceptibility to Amphotericin B and Fluconazole in Candida albicans

Background:

The ability of Candida albicans to form biofilms and adhere to host tissues and biomaterial surfaces is an important factor in its pathogenesis. One of the main characteristics of biofilms is their resistance to broad-spectrum anti-microbial drugs.

Objectives:

In the present study the formation of biofilm by C. albicans from different sources was evaluated. In addition, the minimum biofilm inhibitory concentration (MBIC) for two antifungals was evaluated.

Materials and Methods:

In total, 120 isolates of C. albicans from different sources (patients with vaginitis, patients with candiduria, bucal cavity and environmental surfaces) were collected. Biofilm formation was determined by the 96-well micro-titeration plate method. MBIC testing was also performed, using the calorimetric indicator resazurin for amphotericin B and fluconazole.

Results:

The results indicated that 100% of C. albicans isolates from different sources had the ability to form biofilms in vitro. Amongst these isolates, 83.3% of isolates had the maximum potential (4+) to form biofilms, while only one (0.9%) of isolates had the minimum ability (1+) to form biofilms. Our results showed that 65.0% of the tested isolates are sensitive to amphotericin B at amounts lower than 10 µg/mL, while only 26.7% are sensitive to fluconazole (had MBIC < 10 µg/mL).

Conclusions:

Although biofilm formation was detected in all tested isolates, there were differences in the ability to form biofilms between isolates from different sources. In addition, there were differences in the MBIC against the two examined antifungals, amphotericin B and fluconazole.

Silver sucrose octasulfate (IASOS™) as a valid active ingredient into a novel vaginal gel against human vaginal pathogens: in vitro antimicrobial activity assessment

This in vitro study assessed the antimicrobial properties of a novel octasilver salt of Sucrose Octasulfate (IASOS) as well as of an innovative vaginal gel containing IASOS (SilSOS Femme), against bacterial and yeast pathogens isolated from human clinical cases of symptomatic vaginal infections. In BHI and LAPT culture media, different ionic silver concentrations and different pHs were tested. IASOS exerted a strong antimicrobial activity towards all the pathogens tested in both culture media. The results demonstrated that salts and organic compounds present in the culture media influenced IASOS efficacy only to a moderate extent. Whereas comparable MBCs (Minimal Bactericidal Concentrations) were observed for G. vaginalis (10 mg/L Ag+), E. coli and E. aerogenes (25 mg/L Ag+) in both media, higher MBCs were found for S. aureus and S. agalactiae in LAPT cultures (50 mg/L Ag+ versus 25 mg/L Ag+). No minimal concentration totally inhibiting the growth of C. albicans was found. Nevertheless, in both media at the highest ionic silver concentrations (50-200 mg/L Ag+), a significant 34-52% drop in Candida growth was observed. pH differently affected the antimicrobial properties of IASOS against bacteria or yeasts; however, a stronger antimicrobial activity at pH higher than the physiological pH was generally observed. It can be therefore concluded that IASOS exerts a bactericidal action against all the tested bacteria and a clear fungistatic action against C. albicans. The antimicrobial activity of the whole vaginal gel SilSOS Femme further confirmed the antimicrobial activity of IASOS. Overall, our findings support IASOS as a valid active ingredient into a vaginal gel.

Antistaphylococcal and biofilm inhibitory activities of gallic, caffeic, and chlorogenic acids

Staphylococcus aureus is a Gram-positive pathogen which is able to form biofilms, exhibiting a more pronounced resistance to antibiotics and disinfectants. The hurdles posed in eradicating biofilms have driven the search for new compounds able to fight these structures. Phenolic compounds constitute one of the most numerous and ubiquitous group of plant secondary metabolites with many biological activities. The aim of the present work was to study the potential antimicrobial and antibiofilm properties of gallic, caffeic, and chlorogenic acids against S. aureus as well to elucidate its mechanism of action. It was concluded that the phenolic acids studied in this work have antistaphylococcal properties. For instance, gallic acid is able to influence the adhesion properties of S. aureus. The phenolic acids tested were also able to inhibit the production of α-hemolysin by this microorganism, with the exception of chlorogenic acid. Regarding its mechanism of action, caffeic acid interferes with the stability of the cell membrane and with the metabolic activity of the cells of S. aureus.

Biofilm formation by oral clinical isolates of Candida species

We have conducted a longitudinal study to quantify biofilms in oral clinical isolates of Candida species (spp.) from adults with local and systemic predisposing factors for candidiasis. A total of 69 yeast isolates from 63 Mexican patients were evaluated. These isolates (39 C. albicans, 15 C. tropicalis, 7 C. glabrata, 4 C. krusei, 1 C. lusitaniae, 1 C. kefyr, 1 C. guilliermondii and 1 C. pulcherrima) were obtained from two clinical sites: 62.3% (n=43) from the oral mucosa of totally and partially edentulous patients, and 37.7% (n=26) from the oral mucosa of diabetics. In addition, Candida ATCC strains were used as controls for each experiment. The kinetics of biofilm formation were measured by 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide [XTT] reduction; each isolate was tested at 6, 12 and 24h. Biofilm formation is dependent on the Candida spp. and its clinical origin. On average, the oral isolates of C. glabrata are strong biofilm producers, whereas C. albicans and C. tropicalis are moderate producers. The most common species in our population was C. albicans. While the kinetics of C. albicans biofilm formation varies between oral isolates, it generally maintains steady growth from 2 to 48h, when it reaches its maximum growth.

Candida species: new insights into biofilm formation

Biofilms of Candida albicans, Candida parapsilosis, Candida glabrata and Candida tropicalis are associated with high indices of hospital morbidity and mortality. Major factors involved in the formation and growth of Candida biofilms are the chemical composition of the medical implant and the cell wall adhesins responsible for mediating Candida-Candida, Candida-human host cell and Candida-medical device adhesion. Strategies for elucidating the mechanisms that regulate the formation of Candida biofilms combine tools from biology, chemistry, nanoscience, material science and physics. This review proposes the use of new technologies, such as synchrotron radiation, to study the mechanisms of biofilm formation. In the future, this information is expected to facilitate the design of new materials and antifungal compounds that can eradicate nosocomial Candida infections due to biofilm formation on medical implants. This will reduce dissemination of candidiasis and hopefully improve the quality of life of patients.