Candida albicans biofilm formation on soft denture liners and efficacy of cleaning protocols

doi: 10.1111/j.1741‐2358.2011.00485.x
Candida albicans biofilm formation on soft denture liners and efficacy of cleaning protocols Objective: The aim of this study was to investigate Candida albicans biofilm formation on denture liners and to analyse the efficacy of cleaning protocols. Material and methods: Specimens were prepared from four silicone‐based soft denture liners. After artificial ageing and surface free energy determination, specimens were incubated with saliva (2 h) and Candida albicans ATCC 10231 for either short‐ (2.5 h) or long‐term (24 h) biofilm formation. Adherent cells were determined either after incubation of specimens with Candida albicans or after treatment with different denture cleaning protocols. Statistical analysis was performed using one‐way anova and the Games–Howell test (α = 0.05). Results: For both short‐ and long‐term biofilm formation, similar amounts of Candida albicans cells were found on the surface of the different liners (p = 0.295 and 0.178, respectively). For both short‐ and long‐term biofilm formation, the highest cleaning efficacy was observed for sodium hypochlorite (NaOCl; p < 0.01). The efficacy of the chemical denture cleaner in removing long‐term Candida albicans biofilms was significantly lower than the efficacy of removal by brushing (p < 0.001). Conclusion: Different silicone‐based soft denture liners yield similar Candida albicans biofilm formation on their surface. The highest efficacy for the removal of Candida albicans biofilms was identified for NaOCl. Chemical denture cleaners appear to have rather low efficacy to remove mature Candida albicans biofilms.     

Denture contamination by yeasts in the elderly

Objectives: The aim of this study was to investigate yeast carriage in healthy denture wearers by swabbing and to evaluate the effect of denture hygiene habits. Materials and methods: Denture wearers (n = 87) without evidence of denture stomatitis or any other oral disease were investigated by separately swabbing the fitting surface of the upper denture and the corresponding palatal mucosa in contact with the appliance. In a group of volunteers, a gel without any active compound was spread on the palatal side of the denture once in every morning for 2 weeks. Results: Screening showed Candida colonisation of upper prosthesis in 75.9% of individuals. The most frequent species isolated were Candida albicans (77.9% of the positive cultures), Candida glabrata (44.1%) and Candida tropicalis (19.1%). Carriage of more than one yeast species was found in 48.5% of the contaminated dentures. There was a statistically significant association between denture contamination and palatal mucosa colonisation (chi‐squared test: p < 0.0001). Repeated swabbings after 1 week as well as during a weekly follow‐up for 1 month confirmed the denture contamination and its degree of severity. A daily gel application produced a yeast‐count decrease to 10% of the initial value after 2 weeks (chi‐squared test: p = 0.0134 and p = 0.2841 for prosthesis and palatal mucosa, respectively). Conclusion: This study documented the reliability of oral swabbing when investigating yeast carriage in healthy denture wearers. Moreover, just a diagnostic tool, sampling upper dentures for Candida could be the opportunity to verify the patient’s compliance to hygiene advice.     

In vivo biofilm formation on a soft denture liner in elderly patients with controlled diabetes

doi: 10.1111/j.1741‐2358.2010.00428.x In vivo biofilm formation on a soft denture liner in elderly patients with controlled diabetes Objectives: This in vivo study evaluated the influence of controlled diabetes on biofilm formation on a soft denture liner in elderly patients. Background: Soft denture lining materials are more susceptible to microbial colonisation than denture base acrylic resins. Especially in the elderly, several predisposing factors may accumulate leading to an increased probability of biofilm development that may result in candidiasis, a significant clinical oral disease. Materials and methods: Volunteers wearing complete dentures were divided into two groups (n = 20): diabetic patients with controlled glycaemia, and healthy patients. In both groups, a silicone‐based soft liner was placed in a recess created at the base of the maxillary dentures. Subjects cleaned the prosthesis three times a day. Biofilm formed on the liner was quantified at various time points (baseline, two, four and six weeks). Data were analysed by two‐way repeated measures anova and Tukey’s test (α = 0.05). Results: There was no statistical difference in biofilm formation for any of the time points between controlled diabetes patients and healthy patients. Conclusion: The results suggest that the control of diabetes in elderly patients provides the same levels of biofilm formation when compared to healthy individuals.     

The role of candidal histolytic enzymes on denture-induced stomatitis in patients living in retirement homes

Material and methods: Fifty nine elders wearing complete dentures and living in retirement homes in Curitiba (southern Brazil), were divided into two groups: group #1, 26 patients with denture‐induced stomatitis and group #2, 33 patients without denture‐induced stomatitis. The two groups were evaluated in relation to the degree of denture‐induced stomatitis, salivary fungal loads, and secretion of some histolytic enzymes. Results: Patients from group #1 showed higher degrees of colonisation by Candida albicans (p = 0.031). Candida krusei, Candida tropicalis, and Candida parapsilosis were also isolated, but there were no differences between the groups (p > 0.05). Secretory aspartyl protease (Sap) and chondroitinase did not show significant differences among the isolated Candida spp. in the two groups. Phospholipase secretion rates were higher among the strains of C. albicans from group #2 (p = 0.036). The same behaviour was not detected for non‐albicans Candida species. Conclusions: The results could infer that differences in the secretion rates of candidal histolytic enzymes should not be imputed as imperative for the progress of denture‐induced stomatitis.     

The effect of denture adhesives on Candida albicans growth in vitro

doi: 10.1111/j.1741‐2358.2011.00478.x
The effect of denture adhesives on Candida albicans growth in vitro Objective: Denture‐wearing favours the growth of Candida. In view of the fact that many denture wearers regularly use adhesives to enhance denture retention, stability and function, the aim of this work was to study the effect of denture adhesives on Candida albicans growth in vitro. Materials and methods: The denture adhesives tested were Corega^® cream, Kukident^® cream, Novafix^® cream, Polident^® cream, Protefix^® cream, Steradent^® cream, Aderyn^® powder, Corega^® ultra powder, Protefix^® powder and Corega^® strip. C. albicans growth curves were obtained in the presence or absence of a 1% solution of the denture adhesive diluted in Sabouraud broth. Macro‐ and microscopic morphological changes in C. albicans were analysed, as was microbial contamination of the denture adhesive. Results: Most of the denture adhesives studied induced morphological changes in C. albicans cells and colonies, but only two had any significant inhibitory effect on yeast growth. Kukident^® cream markedly inhibited C. albicans growth in a concentration‐dependent way, reducing the growth rate by 95%, whereas Corega^® cream also inhibited C. albicans growth but in a non‐concentration‐dependent way, reducing the growth rate by 37%. In addition, denture adhesives available as powders had detectable microbial contamination. Conclusion: Some commercially available denture adhesives showed microbial contamination and some had significant inhibitory effect on C. albicans growth.     

The carriage of Candida species on the dorsal surface of the tongue: the correlation with the dental, periodontal and prosthetic status in elderly subjects

Objectives: To screen the carriage status of Candida species, especially Candida albicans and its genotype in an epidemiological survey and to investigate its correlation with the dental, periodontal and prosthetic status of healthy elderly subjects. Materials and methods: Microbiological samples were collected from the dorsum of the tongue of 366 subjects, aged 75, and cultured on CHROMagar medium. The carriage status of Candida spp. and the distribution of C. albicans genotypes by a polymerase chain reaction (PCR) method were analysed and compared with the dental, periodontal and prosthetic status of the subjects. Results: A high carriage rate (68.6%) of Candida spp. and the predominant species of C. albicans (72.1%) were found in this study. The prevalence, density and multi‐species of Candida spp. were significantly related to the presence of a dental prosthesis. In C. albicans, genotype A predominated (56.4%) and genotype D showed a higher prevalence (12.5%) than previous reports. When comparing Candida spp. carriage with the oral status, significant positive correlations were found with the presence of any dental prosthesis, missing teeth, the number of retained roots and the percentage of sites showing bleeding on probing (BOP), while significant negative correlations were found with the number of teeth present, sound and filled teeth. Conclusions: Candida carriage on the dorsum of the tongue in healthy elderly is significantly associated with the dental, periodontal and prosthetic status, especially the presence of a dental prosthesis. As the complexity of the prosthesis being worn increased, the relative risk of Candida carriage and the numbers and multi‐species of Candida increased accordingly.     

Pathogenic factors in Candida biofilm‐related infectious diseases

Candida albicans is a commonly found member of the human microflora and is a major human opportunistic fungal pathogen. A perturbation of the microbiome can lead to infectious diseases caused by various micro‐organisms, including C. albicans. Moreover, the interactions between C. albicans and bacteria are considered to play critical roles in human health. The major biological feature of C. albicans, which impacts human health, resides in its ability to form biofilms. In particular, the extracellular matrix (ECM) of Candida biofilm plays a multifaceted role and therefore may be considered as a highly attractive target to combat biofilm‐related infectious diseases. In addition, extracellular DNA (eDNA) also plays a crucial role in Candida biofilm formation and its structural integrity and induces the morphological transition from yeast to the hyphal growth form during C. albicans biofilm development. This review focuses on pathogenic factors such as eDNA in Candida biofilm formation and its ECM production and provides meaningful information for future studies to develop a novel strategy to battle infectious diseases elicited by Candida‐formed biofilm.     

The effect of accelerated ageing on colour stability of visible light-cured (VLC) chairside denture liners

doi: 10.1111/j.1741‐2358.2011.00458.x
The effect of accelerated ageing on colour stability of visible light–cured (VLC) chairside denture liners Objective: The purpose of this study was to assess the colour stability of seven visible light–cured (VLC) hard and soft denture liners by an in vitro accelerated ageing test and compare them with two autopolymerised hard and soft liners. Materials and methods: Ten specimens of each material were fabricated. The initial colour was measured with a tri‐stimulus colorimeter. One set of five specimens was placed in distilled water at 37°C in the dark for 15 days, while the remaining were subjected to UV/visible light‐accelerated ageing initially for 24 h and then for 144 h. Colour change (ΔΕ) was calculated. Data were statistically analysed by anova , Tukey and t‐tests at α = 0.05. Results: All the liners showed clinically acceptable colour change (ΔΕ ≤ 6.8) in distilled water. The colour changes after ageing for Triad DuaLine, Lightdon U, Ufi Gel H and Light Liner Hard were clinically unacceptable (ΔΕ ≥ 6.8), whereas LightLiner Soft, Astron LC Soft, Triad Resiline and Flexacryl Soft presented slighter and clinically acceptable colour change (ΔΕ ≤ 6.8). Conclusion: Accelerated ageing affected significantly the colour stability of all denture liners tested except Astron LC Soft. Soft VLC denture liners were more colour‐stable than hard VLC liners.     

Effect of denture adhesive on the micro-organisms in vivo

doi: 10.1111/j.1741‐2358.2010.00381.x Effect of denture adhesive on the micro‐organisms in vivo Background: Denture adhesives increase the retention and stability of dentures in edentulous patients, especially in cases where salivary flow is impaired or in the management of traumatised oral mucosa. Objectives: The effect of a denture adhesive on the oral flora at different time intervals. Method: Thirty denture‐wearing patients were involved in this study. While half of the group received a denture adhesive, the other half did not. At baseline, 1 and 2 months after delivering the dentures, smear samples were obtained from the saliva, palate and the dentures. Candida albicans, Candida krusei, Candida glabrata, Candida spp., Staphylococcus aureus, Moraxella catarrhalis, α‐haemolytic streptococci, β‐haemolytic streptococci, Pneumococcus aureus, S. anginosus, S. intermedius, S. constellatus, S. sanguis, S. gordonii, S. mitis, S. mutans, S. salivarius, and yeasts were investigated. The data were statistically analysed using anova and repeated measures. Results: Most types of the micro‐organisms were not seen and could not be analysed statistically except α‐haemolytic streptococci and C. albicans. No statistically significant difference was found for α‐haemolytic streptococci and C. albicans in saliva, palate and the denture at all time intervals. Conclusions: Prolonged use of the denture adhesive tested up to 2 months did not yield to increase in micro‐organisms of the oral flora.     

Susceptibility of <Emphasis Type="Italic">Candida</Emphasis> biofilms to histatin 5 and fluconazole

Candida-associated denture stomatitis has a high rate of recurrence. Candida biofilms formed on denture acrylic are more resistant to antifungals than planktonic yeasts. Histatins, a family of basic peptides secreted by the major salivary glands in humans, especially histatin 5, possess significant antifungal properties. We examined antifungal activities of histatin 5 against planktonic or biofilm Candida albicans and Candida glabrata. Candida biofilms were developed on poly(methyl methacrylate) discs and treated with histatin 5 (0.01–100 μM) or fluconazole (1–200 μM). The metabolic activity of the biofilms was measured by the XTT reduction assay. The fungicidal activity of histatin 5 against planktonic Candida was tested by microdilution plate assay. Biofilm and planktonic C. albicans GDH18, UTR-14 and 6122/06 were highly susceptible to histatin 5, with 50% RMA (concentration of the agent causing 50% reduction in the metabolic activity; biofilm) of 4.6 ± 2.2, 6.9 ± 3.7 and 1.7 ± 1.5 μM, and IC₅₀ (planktonic cells) of 3.0 ± 0.5, 2.6 ± 0.1 and 4.8 ± 0.5, respectively. Biofilms of C. glabrata GDH1407 and 6115/06 were less susceptible to histatin 5, with 50% RMA of 31.2 ± 4.8 and 62.5 ± 0.7 μM, respectively. Planktonic C. glabrata was insensitive to histatin 5 (IC₅₀ > 100 μM). Biofilm-associated Candida was highly resistant to fluconazole in the range 1–200 μM; e.g. at 100 μM only ~20% inhibition was observed for C. albicans, and ~30% inhibition for C. glabrata. These results indicate that histatin 5 exhibits antifungal activity against biofilms of C. albicans and C. glabrata developed on denture acrylic. C. glabrata is significantly less sensitive to histatin 5 than C. albicans.     

In vivo assessment of the effect of an adhesive for complete dentures on colonisation of Candida species

doi: 10.1111/j.1741‐2358.2009.00345.x
In vivo assessment of the effect of an adhesive for complete dentures on colonisation of Candida species Objective: Denture adhesives have long been recognised by denture wearers as a useful adjunct to denture retention and stability. The objective of the present study was to evaluate, in vivo, the effect of a denture adhesive on oral quantities of Candida species by determination of absolute counts of colony‐forming units (CFU) per ml of saliva of individuals who use this denture adhesive for a period of 14 days. Materials and methods: Twenty‐four individuals were randomised in two equal groups of 12 (test and control), with the individuals of the test group using the adhesive for 14 days. Samples of saliva were collected from all individuals on days 0 (initial), 7 and 14. Aliquots of saliva were diluted and plated in duplicate on Sabouraud dextrose agar with chloramphenicol and incubated for 37°C for 48 h, the CFU/ml were counted in the individuals of each group and the data of each group were compared at the different time periods and analysed statistically by the non‐parametric Mann‐Whitney U‐test (α ≤ 5%). Results: There were no statistically significant differences between the test and control groups during the test periods. Conclusion: Within of the limitations of this study, the data suggested that the denture adhesive tested did not significantly alter the oral microbiota during the 14‐day trial period.     

Determining <Emphasis Type="Italic">Candida</Emphasis> spp. Incidence in Denture Wearers

The aim of this study was to determine Candida spp. incidence in the oral cavity of denture wearers and characterize predisposing factors in denture-related stomatitis (DRS). Three groups of denture wearers and a control group were evaluated for DRS according to Newton’s classification. The amount of yeast in saliva and the presence of yeast on mucosal surfaces were determined by phenotyping methods, and the impact of some risk factors on candidal carriage was evaluated. The development of DRS is most common in complete prosthesis users. When the count of yeast in saliva is ≥400 cfu/ml, the frequency of DRS is increased. In individuals who develop DRS, the most frequently encountered species that was identified as C. albicans. Prosthetic hygiene was related to the intensity of candidal growth and the development of DRS. C. albicans live as saprophyte in the oral cavity. But, it is capable of causing infection if there are predisposing conditions related to the host. Usage of removable prosthesis may cause these microorganisms to gain pathogenicity.     

Effervescent tablets and ultrasonic devices against Candida and mutans streptococci in denture biofilm

doi: 10.1111/j.1741‐2358.2010.00378.x Effervescent tablets and ultrasonic devices against Candida and mutans streptococci in denture biofilm Objective: To evaluate the antimicrobial action of effervescent tablets and ultrasound on Candida spp. and mutans streptococci from denture biofilm. Background: It is not uncommon for edentulous patients to be elderly and find it difficult to brush their dentures. Hence, auxiliary methods are required for cleansing dentures as well as treating oral infections. Materials and methods: Seventy‐seven complete denture wearers were randomly assigned into four groups: (A) Brushing with water (control); (B) Effervescent tablets; (C) Ultrasonic device (Ultrasonic Cleaner, model 2840 D); (D) Effervescent tablets and ultrasonic device. All groups brushed their dentures with a specific brush and water, three times a day, before applying their treatments. Denture biofilm was collected at baseline and after 21 days. The samples were collected by brushing the dentures with saline and the detached microbial cells were quantified by plating. Counts [log (CFU+1) ml^?1] of total aerobes, Candida spp. and mutans streptococci were compared by one‐way anova or Kruskal–Wallis test (α = 0.05). Results: No significant difference was found among the methods from C. albicans (p = 0.76), C. tropicalis (p = 0.94) and C. glabrata (p = 0.80). Lower counts were found for methods B and D when compared with the other methods against mutans streptococci (p < 0.001). Method B showed lower total aerobic counts than A, whereas C and D showed intermediate results (p = 0.011). Conclusion: The effervescent tablets significantly reduced mutans streptococci and total aerobes from denture biofilm. However, they was not as effective against C. albicans. Ultrasonic cleansing presented a discrete antimicrobial effect and was less effective than the tablets for complete denture disinfection.     

Biofilm formation of Candida albicans on the surface of a soft denture‐lining material

Background: Soft denture lining‐materials are more susceptible to microbial adhesion than hard denture base acrylic resin. Poor oral hygiene and Candida albicans infection are common among elderly denture wearers as these patients usually have difficulty in keeping them clean. Purpose: To evaluate the influence of the oral hygiene methods on the formation of a biofilm over a soft denture‐lining material. Material and methods: Twenty volunteers were randomly separated into two groups: G1 and G2. Ten volunteers performed daily hygiene of the prostheses with a soft toothbrush and toothpaste. The G2 performed a treatment identical to G1 but also immersed the prostheses in sodium hypochlorite 0.5% for 20 min, once a week. Quantification of the mean score values of biofilm formation at different times were statistically analysed using analysis of variance and Tukey’s test (α = 0.05). Results: G1 (0.65 ± 0.52) showed the lowest mean score values of biofilm formation. There was statistical difference between G1 and G2. The highest mean score values were found at 6 weeks (1.3 ± 1.08) and were statistically different from other times. Conclusion: The oral hygiene methods had a significant effect in the formation of the biofilm over a soft denture‐lining material.     

Towards non‐invasive monitoring of pathogen–host interactions during Candida albicans biofilm formation using in vivo bioluminescence

Candida albicans is a major human fungal pathogen causing mucosal and deep tissue infections of which the majority is associated with biofilm formation on medical implants. Biofilms have a huge impact on public health, as fungal biofilms are highly resistant against most antimycotics. Animal models of biofilm formation are indispensable for improving our understanding of biofilm development inside the host, their antifungal resistance and their interaction with the host immune defence system. In currently used models, evaluation of biofilm development or the efficacy of antifungal treatment is limited to ex vivo analyses, requiring host sacrifice, which excludes longitudinal monitoring of dynamic processes during biofilm formation in the live host. In this study, we have demonstrated for the first time that non‐invasive, dynamic imaging and quantification of in vitro and in vivo C. albicans biofilm formation including morphogenesis from the yeast to hyphae state is feasible by using growth‐phase dependent bioluminescent C. albicans strains in a subcutaneous catheter model in rodents. We have shown the defect in biofilm formation of a bioluminescent bcr1 mutant strain. This approach has immediate applications for the screening and validation ofantimycotics under in vivo conditions, for studying host–biofilm interactions in different transgenic mouse models and for testing the virulence of luminescent C. albicans mutants, hereby contributing to a better understanding of the pathogenesis of biofilm‐associated yeast infections.     

In vitro and clinical evaluation of specific dentifrices for complete denture hygiene

Objectives: To study the physical properties of two experimental dentifrices for complete denture hygiene, their effect on denture biofilm removal and antimicrobial properties by means of a clinical trial. Materials and methods: The experimental dentifrices comprised two compositions. One was based on the addition of 1% chloramine T (D1) and the other on the presence of 0.01% fluorosurfactant (D2). Measurements of density, pH, consistency, rheological features and abrasiveness were conducted. Sixty complete denture wearers were randomly assigned to three groups and were instructed to brush their dentures with a specific toothbrush: (1) Water (control); (2) D1; or (3) D2. Each method was used for 21 days. Denture biofilm was disclosed by a 1% neutral red solution and quantified by means of digital photos taken from the internal surface. Microbiological assessment was conducted to quantify Candida sp. and mutans streptococci. Data were evaluated by one‐way anova and Tukey HSD, or Kruskal–Wallis (α = 0.05). Results: Both dentifrices decreased biofilm coverage when compared with the control group. D1 was the most efficacious treatment to reduce mutans streptococci, whereas D2 showed an intermediate outcome (anova , p < 0.040). No treatment influenced Candida albicans or non‐albicans species (Kruskal–Wallis, p = 0.163 and 0.746, respectively). Conclusion: It can be concluded that brushing complete dentures with the experimental dentifrices tested could be effective for the removal of denture biofilm.     

The synergy of honokiol and fluconazole against clinical isolates of azole‐resistant Candida albicans

Aims: To evaluate the interaction of fluconazole (FLC) and honokiol (HNK) in vitro and vivo against azole‐resistant (azole‐R) clinical isolates of Candida albicans. Methods and Results: A checkerboard microdilution method was used to study the in vitro interaction of FLC and HNK in 24 azole‐R clinical isolates of C. albicans. In vivo antifungal activity was performed to further analyse the interaction between FLC and HNK. In the in vitro study, synergism was observed in all 24 FLC‐resistant strains tested as determined by fractional inhibitory concentration index (FICI), and in 22 strains by ΔE models. No antagonistic activity was observed in any of the strains tested. These positive interactions were also confirmed by using the time‐killing test for the selected strain C. albicans YL371, which shows strong susceptible to the combination of HNK and FLC. In the in vivo study, the mice with candidiasis were treated successfully by a combination therapy of HNK with FLC, the results showed a decrease of the colony forming unit in infected and treated animals compared to the controls, at the conditions of the treatment used in this study. Conclusions: Synergistic activity of HNK and FLC against clinical isolates of FLC‐resistant C. albicans was observed in vitro and in vivo. Significance and Impact of the Study: This report might provide a potential therapeutic method to overcome the problem of drug‐resistance in C. albicans.     

Virulence and pathogenicity of Candida albicans is enhanced in biofilms containing oral bacteria

This study examined the influence of bacteria on the virulence and pathogenicity of candidal biofilms. Mature biofilms (Candida albicans-only, bacteria-only, C. albicans with bacteria) were generated on acrylic and either analysed directly, or used to infect a reconstituted human oral epithelium (RHOE). Analyses included Candida hyphae enumeration and assessment of Candida virulence gene expression. Lactate dehydrogenase (LDH) activity and Candida tissue invasion following biofilm infection of the RHOE were also measured. Candida hyphae were more prevalent (p < 0.05) in acrylic biofilms also containing bacteria, with genes encoding secreted aspartyl-proteinases (SAP4/SAP6) and hyphal-wall protein (HWP1) up-regulated (p < 0.05). Candida adhesin genes (ALS3/EPA1), SAP6 and HWP1 were up-regulated in mixed-species biofilm infections of RHOE. Multi-species infections exhibited higher hyphal proportions (p < 0.05), up-regulation of IL-18, higher LDH activity and tissue invasion. As the presence of bacteria in acrylic biofilms promoted Candida virulence, consideration should be given to the bacterial component when managing denture biofilm associated candidoses.     

Biofilm formation by Candida albicans on various prosthetic materials and its fluconazole sensitivity: a kinetic study

Candida albicans has the ability to colonize various materials used in prostheses. In this report, we have studied the kinetics of biofilm formation on prosthetic materials and their susceptibility to fluconazole at various stages of development. Results indicated that C. albicans efficiently adheres to and colonizes polystyrene, polyvinylchloride, silicon, and polycarbonate surfaces. Candida albicans biofilm formation was observed to be both strain- and substrate dependent. Adhesion of cells to solid substrates was found sufficient to induce fluconazole resistance. Drug susceptibility at different stages of biofilm growth showed that Candida biofilms on these substrates are highly resistant to fluconazole. The study focuses on the limitations of fluconazole to combat biofilm-related infections and emphasizes the need for better therapeutic strategies against prosthesis-associated C. albicans infections.