The expression of the secreted aspartyl proteinases Sap4 to Sap6 from Candida albicans in murine macrophages

Medically important yeasts of the genus Candida secrete aspartyl proteinases (Sap), which are of particular interest as virulence factors. Six closely related gene sequences, SAP1 to SAP6, for secreted proteinases are present in Candida albicans. The methylotrophic yeast Pichia pastoris was chosen as an expression system for preparing substantial amounts of each Sap isoenzyme. Interestingly, Sap4, Sap5 and Sap6, which have not yet been detected in C. albicans cultures in vitro, were produced as active recombinant enzymes. Different Sap polyclonal antibodies were raised in rabbits and tested before further application by enzyme-linked immunosorbent assay (ELISA) against each recombinant Sap. Two antisera recognized only Sap4 to Sap6. Using these antisera, together with sap null mutants obtained by targeted mutagenesis, we could demonstrate a high production of Sap4, Sap5 and Sap6 by C. albicans cells after phagocytosis by murine peritoneal macrophages. Furthermore, a delta sap4,5,6 null mutant was killed 53% more effectively after contact with macrophages than the wild-type strain. These results support a role for Sap4 to Sap6 in pathogenicity.     

HIV protease inhibitors influence the prevalence of oral candidosis in HIV-infected patients: a 2-year study

The introduction of HIV protease inhibitors was accompanied by reduction in HIV-associated opportunistic infections. Therefore, we performed a retrospective study of HIV-infected patients to evaluate the effects of therapy with an HIV protease inhibitor (PI) on oral candidosis. This was of special interest, because an important virulence factor of Candida albicans is the secreted aspartic protease (SAP), which is assigned to the same class of aspartic proteases as HIV protease. Sixty-two patients were examined five times over a period of 2 years. There was a hint at a difference in the frequencies of C. albicans carrier state and manifest oral candidosis in favour of treatment with a PI. In addition, loss of Candida colonization and manifest oral candidosis was observed only in patients with elevation of CD4 cells upon PI. This might explain the effect, which also might go back to a direct inhibition of yeast SAP.     

The possible influence of the menstrual cycle on the adherence of Candida albicans to human buccal epithelial cells in vitro

Although the influence of the menstrual cycle on both vaginal candidosis and Candida albicans adherence to vaginal epithelial cells in vitro has been shown to be significant, similar studies have not been made on oral candidosis and adherence to buccal epithelial cells. The aim of this study was therefore to use an in vitro adherence assay to investigate the possible influence of the menstrual cycle on the adherence of C. albicans to buccal epithelial cells. Epithelial cells were collected from a single, healthy, female volunteer on days 5, 15, 22 and 28 of six menstrual cycles. Adherence of C. albicans was significantly higher to buccal epithelial cells collected on day 5 of the menstrual cycle when compared with days 15, 22 and 28, both in terms of the percentage of buccal epithelial cells with adherent C. albicans and the number of C. albicans adhering per 200 buccal epithelial cells in four out of six menstrual cycles (p < 0.001). This result indicates that hormonal influences should be considered when buccal epithelial cells are used in vitro to assess candidal adherence and may implicate hormonal factors in the aetiology of oral candidosis.     

Candida albicans morphotypes and in vitro adhesivity to cells of the human oral mucosa in HIV-positive and AIDS patients after exposure of blastospores to fluconazole. II

BACKGROUND: Oro-pharyngeal candidosis is a frequently initial clinical manifestation of HIV infection and the adhesive properties of Candida spp. represent a very important pathogenicity factor. METHODS: In this study the adhesivity rate of Candida albicans to the oral epithelial cells of 33 HIV-positive patients and 12 healthy volunteers, have been assessed before and after the exposure of blastospores to inhibitory concentrations of fluconazole, in relation to 11 morphotypes obtained from 13 C. albicans strains. RESULTS: Results can be summarized as follows: 1) the number of blastospores adhering to the HIV-positive donor' cells is higher than that of blastospores adhering to the healthy donors' cells (rate is 2.7:1); 2) blastospores from strains producing rough or very coarse fringes show adhesive properties higher than those of strains with different morphology; 3) in the group of HIV-positive patients the adhesivity inhibition of blastospores from strains producing rough or very coarse fringes was higher (38.3%) than that of strains with different morphology (33.8%); 4) overall, adhesivity inhibition due to exposure to fluconazole is higher for epithelial cells from healthy donors. CONCLUSIONS: These results can suggest the validity of an antimycotic pretreatment of persons at risk of oro-pharyngeal candidiasis.     

Candida albicans secreted aspartyl proteinases

Evidence suggests that infections with the opportunistic yeast Candida albicans are caused by several factors. Among these virulence attributes, secreted aspartyl proteinases (Saps) are widely believed to play a role during pathogenesis. Sap isoenzymes are encoded by at least eight closely related SAP genes. Antigen-antibody studies provided evidence that Sap isoenzymes are expressed in vivo and experimental infections with proteinase deficient mutants suggested a role for Saps in the virulence of C. albicans. However, only one gene product, Sap2, has been characterized in detail. In vitro studies with purified Sap(2) suggested several possible host targets but the role of each Sap isoenzyme remains unclear. The expression pattern of SAP genes proposed that Sap isoenzymes are secreted simultaneously with morphological changes such as the yeast to hyphal transition or during phenotypic switching. In addition, extracellular proteolytic activity may affect adhesion to host cells and thus may help the fungus to persist on host surfaces and to penetrate into deeper tissue. This review will deal with secretory proteinases from C. albicans as putative virulence factors and will focus on the more recent molecular aspects of the proteinases and their genes. Insights into the genetic organization and regulation of the secreted proteinases suggest not only that these enzymes may act as virulence factors of C. albicans, but that the pathogenesis of this fungus is indeed complex and multifactorial.     

Nystatin pastilles and suspension in the treatment of oral candidosis

Clinical audit revealed that the treatment of oral candidosis was more successful with nystatin pastilles than with nystatin suspension. The purpose of this investigation was to determine the reasons for this observation. The concentration of nystatin needed to kill 49 consecutive clinical isolates of Candida albicans was measured. The isolates varied in cidal concentrations from 1.875 to 30 U/ml. The time taken to kill these isolates at their cidal concentrations was found to vary from 120 to 300 min. Volunteer studies showed that antifungal activity in the oral cavity was eliminated rapidly after the use of nystatin suspension. In contrast, the polyene could be detected for at least 5 hours after use of the nystatin pastille. The nystatin pastille can be expected to be more effective at killing Candida albicans than the suspension due to its persistent effects.     

Secreted aspartyl proteinases and interactions of Candida albicans with human endothelial cells

The endothelial cell interactions of homozygous null mutants of Candida albicans that were deficient in secreted aspartyl proteinase 1 (Sap1), Sap2, or Sap3 were investigated. Only Sap2 was found to contribute to the ability of C. albicans to damage endothelial cells and stimulate them to express E-selectin. None of the Saps studied appears to play a role in C. albicans adherence to endothelial cells.     

Adhesion of oral Candida albicans isolates to denture acrylic following limited exposure to antifungal agents

Candidal adherence to denture acrylic surfaces is implicated as the first step in the pathogenesis of Candida-associated denture stomatitis, the most prevalent form of oral candidosis in the West. This condition is treated by topically administered antifungal agents, mainly belonging to the polyenes and azoles. As the intraoral concentrations of antifungals fluctuate considerably due to the dynamics of the oral environment, the effect of short exposure to sublethal concentrations of antifungals on the adhesion of Candida albicans to denture acrylic surfaces was investigated. Seven oral C. albicans isolates were exposed to four-eight times minimum inhibitory concentrations (MIC) of five antifungal drugs, nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole, for 1 h. After removing the drug (by repeated washing) the adhesion of these isolates to acrylic strips was assessed by an in vitro adhesion assay. Exposure to antifungal agents significantly reduced the adherence of all seven C. albicans isolates to denture acrylic. The mean percentage reductions of adhesion after limited exposure to nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole were 86.48, 90.85, 66.72, 65.88 and 47.42%, respectively. These findings indicate that subtherapeutic doses of antifungals may modulate oral candidal colonization. Further, these results may have an important bearing on dosage regimens currently employed in treating oral candidosis.     

Prophylaxis of Candida and Aspergillus infections with oral administration of itraconazole

The broad-spectrum oral triazole antifungal, itraconazole, has been shown to be effective in the treatment of superficial and systemic infections with fungi including Candida albicans, C. krusei and C. glabrata, Cryptococcus, Aspergillus, Histoplasma, Blastomyces and others. Its broad spectrum of activity, high and persistent tissue levels and favourable safety profile suggest that it may be appropriate for the prevention of opportunistic fungal infections in at-risk patients. In this study, itraconazole's prophylactic efficacy was tested against experimental models of Candida and Aspergillus infection. A single dose of 1.25 mg kg-1 or 2.5 mg kg-1, given 1 h before vaginal infection with C. albicans, protected 50% of treated rats. In systemic and disseminated candidosis, prophylaxis with itraconazole reduced both folliculitis and organ Candida content in guinea pigs. Amphotericin B was also used in this study and was found to be less efficacious than itraconazole. Itraconazole prolonged survival when administered to guinea pigs before experimental induction of systemic and invasive aspergillosis. In all cases, increasing the itraconazole dosage increased its prophylactic efficacy. Therefore, as the clinical efficacy of itraconazole is accurately reflected by the results of animal models, this study shows itraconazole to be a potential prophylactic therapy for patients at risk of opportunistic fungal infection.     

Comparison of four methods of automated recording of physiologic data at one minute intervals

OBJECTIVES: To provide the clinical profile and assess the significance of various risk factors contributing to the occurrence of oral candidosis in newborns. DESIGN: Case-control study. SETTING: Neonatal Intensive Care Unit (NICU). SUBJECTS: Twenty newborns with oral candidosis and an equal number of age and weight matched controls. INTERVENTIONS: All cases of oral candidosis were treated with local application of 1% Clotrimazole. RESULTS: Oral candidosis was documented in 3.2% (20/650) cases in the NICU. Acute pseudomembranous candidosis was the most common presentation. The mean age of onset was 10.5 days. Candida albicans was isolated in 50% cases in addition to C. tropicalis, C. paratropicalis, C. krusei, C. glabrata and C. parapsilosis. On univariate analysis, male sex, birth asphyxia and prolonged antibiotic therapy had a significant correlation with occurence of oral candidosis in neonates. Out of these, birth asphyxia was the only factor significantly associated with oral candidosis (OR 8.09, 95% CI 1.34-48.8, p = 0.0226) on multivariate analysis. CONCLUSIONS: C. albicans was the predominant isolate in this series of oral candidosis. Clinical manifestations were evident in the second week of life and birth asphyxia was the most important associated perinatal event.     

Clinically significant azole cross-resistance in Candida isolates from HIV-positive patients with oral candidosis

OBJECTIVES: To determine the proportion of fluconazole-resistant Candida albicans isolates that have clinically significant cross-resistance to itraconazole or ketoconazole, that is sufficient to result in failure of these agents at their standard doses (200 and 400 mg daily for 7 days, respectively). METHODS: Seven hundred C. albicans isolates from HIV-positive patients with oral candidosis underwent susceptibility testing using a relative growth method, for which cut-off values corresponding to clinical drug failure have been established. RESULTS: A total of 431 isolates were fully azole-susceptible and three main resistance patterns were detected: isolates resistant to fluconazole alone (n = 100); isolates resistant to fluconazole and ketoconazole but susceptible to itraconazole (n = 94); and isolates resistant to all three drugs (n = 50). No isolates were consistently resistant to ketoconazole without being fluconazole-resistant, and no itraconazole resistance was detected without ketoconazole resistance. Resistance to fluconazole alone was more common in specimens obtained soon after first clinical fluconazole failure, whereas specimens from patients with a longer history of fluconazole-unresponsive candidosis were more likely to be infected with cross-resistant isolates. Median days of prior azole exposure and cumulative fluconazole dose were significantly less for those with isolates resistant to fluconazole alone than for those with ketoconazole cross-resistant isolates, who had received less azole therapy and smaller cumulative fluconazole doses than those with isolates cross-resistant to all three drugs (although not statistically significant). After the diagnosis of fluconazole-unresponsive candidosis, increasing cumulative doses of itraconazole solution were associated with increasing likelihood of cross-resistance. CONCLUSIONS: Clinically significant cross-resistance to other azoles may occur in fluconazole-resistant isolates of C. albicans, although initially most isolates are not cross-resistant and the detection of cross-resistant isolates is associated with a history of greater prior azole exposure. Patients who have been treated for fluconazole-resistant candidosis for longer and with greater cumulative doses of itraconazole solution tend to become infected with increasingly cross-resistant isolates of C. albicans.     

Autoimmune hepatitis and autoimmune manifestations in patients with chronic viral hepatitis

Mucosal adherence and germ tube formation have been considered as important virulence factors of Candida albicans. We investigated 11 clinical isolates (among them six isolates from oesophageal thrush) for quantification of adherence to buccal epithelial cells and germ tube formation in the continuous flow culture in vitro, and correlated the results with the clinical data of the patients. Adherence varied considerably between the different C. albicans strains. Strains recovered from clinically, culturally and serologically confirmed oesophageal thrush adhered stronger to buccal epithelial cells. Isolates from cases with heavy colonisation but clinically without candidosis were less adherent. Only after 30 min germ tube formation was observed in the continuous flow culture. Strains with stronger adherence also showed significantly faster and increased germ tube formation. The patients with oesophageal thrush did not suffer any particular immunosuppression such as HIV infection, although in most cases chronic alcoholism was apparent. We conclude, that in cases with minor immunosuppression the expression of the virulence factors adherence and germ tube formation plays an important role in the pathogenesis of candidosis, whereas it may be of less importance in cases with severe immunosuppression. In the latter they may, however, influence outcome.     

Collagenase-3 (matrix metalloproteinase-13) expression is induced in oral mucosal epithelium during chronic inflammation

Increased proliferation of mucosal epithelium during inflammation is associated with degradation of subepithelial connective tissue matrix and local invasion of the epithelial cells. Here we have studied, whether collagenase-3 (MMP-13), a collagenolytic matrix metalloproteinase with an exceptionally wide substrate specificity, is expressed in the epithelium of chronically inflamed mucosa. Examination of human gingival tissue sections from subjects with chronic adult periodontitis with in situ hybridization revealed marked expression of MMP-13 in basal cells of some epithelial rete ridges expanding into connective tissue. Immunohistochemical staining demonstrated that these cells also expressed strongly laminin-5, suggesting that they are actively migrating cells. A strong signal for MMP-13 mRNA was occasionally also noted in the suprabasal epithelial cells facing the gingival pocket, whereas no collagenase-1 (MMP-1) mRNA was detected in any areas of the epithelium. MMP-13 expression was also detected in fibroblast-like cells associated with collagen fibers of the inflamed subepithelial connective tissue. In organ culture of human oral mucosa, MMP-13 mRNA expression was observed in epithelial cells growing into connective tissue of the specimens. Regulation of MMP-13 expression was examined in cultured normal nonkeratinizing epithelial cells isolated from porcine periodontal ligament. In these cells, MMP-13 expression at the mRNA and protein level was potently enhanced (up to sixfold) by tumor necrosis factor-alpha, transforming growth factor-beta(1), and transforming growth factor-alpha and by keratinocyte growth factor in the presence of heparin. In addition, plating periodontal ligament epithelial cells on type I collagen stimulated MMP-13 expression (sevenfold) as compared with cells grown on tissue culture plastic. The results of this study show, that expression of MMP-13 is specifically induced in undifferentiated epithelial cells during chronic inflammation due to exposure to cytokines and collagen. Thus, it is likely that MMP-13 expression is instrumental in the subepithelial collagenolysis and local invasion of the activated mucosal epithelium into the connective tissue.     

Phenotypic and genotypic characterization of oral yeasts from Finland and the United States

A total of 4-22 isolates of oral yeasts per subjects from 48 yeast-positive Finnish and American subjects (25 females and 23 males) were phenotyped and genotyped to determine the frequency of simultaneous oral carriage of multiple yeast taxa. An oral sample from either periodontal pockets, oral mucosa or saliva was obtained. All subjects yielded Candida albicans and 3 subjects an additional yeast species (Candida krusei, Candida glabrata or Saccharomyces cerevisiae). The API 20C Aux kit distinguished 9 different carbohydrate assimilation profiles among the C. albicans isolates. Thirty-eight of 46 C. albicans biotype I isolates were categorized in a single numerical profile. PCR analysis, using a random primer OPA-03 and a repetitive primer (GACA)4, detected 2 major genotypic groups among the C. albicans isolates; 44 subjects showing isolates with a "typical" PCR-profile and 4 subjects isolates with an "atypical" PCR-profile. The "atypical" PCR-profile was similar to that of Candida dubliniensis. All C. albicans isolates assimilated xylose, except 5, including the 4 with an "atypical" PCR-profile. No difference was found in distribution of oral yeast species, and of C. albicans phenotypes and genotypes between Finnish and American subjects. The present PCR method may offer a rapid and easy means of distinguishing oral Candida species.     

Induced candidosis in mice with artificially established oral flora

The aim of this study was to gauge the effect of an artificially established flora, unnatural for mice, on the induction of oral candidosis in mice. Four groups of BALB/c mice were compared; conventional Candida albicans-free mice, "germ-free" mice which had been inoculated with Candida-free human saliva, germ-free mice which had been exposed to a cocktail of Streptococcus mitis, S. sobrinus and S. sanguis, and uncontaminated germ-free mice. After exposure to C. albicans via drinking water, the four groups of mice were killed and their oral cavities examined for candidal growth and oral lesions. Conventional mice yielded significantly less candidal growth and exhibited significantly fewer oral lesions than the other three groups. Candidal lesions in the two groups of contaminated germ-free mice were significantly fewer than in the uncontaminated germ-free mice. The latter exhibited extensive candidal lesions with little inflammatory infiltrate. It is concluded that mice with human oral micro-organisms have some resistance against candidal infection albeit at a reduced level, that mice with natural oral flora are highly resistant, and that germ-free mice are extremely susceptible to C. albicans infection.     

Clinical use of oral nystatin in the prevention of systemic candidosis in patients at particular risk

Systemic candidosis is currently a major concern among certain groups of patients at particular risk because of recent treatment modalities. To prevent spread of Candida albicans, in particular, from the orogastrointestinal tract antimycotic treatment would appear beneficial. So far, however, suitable drugs are rare. Polyenes, and in particular oral nystatin, are the main ones considered so far. More recently, the oral azoles have provided therapeutic alternatives. In this review the current role of nystatin and, in particular nystatin tablets, which are better accepted than suspensions at higher dose levels, is described, focusing on efficacy and safety as determined in controlled trials. Recent evidence suggests that oral application of nystatin tablets can be considered both efficacious and safe in the appropriate context. The relative potency of oral nystatin and systemic azoles, particularly ketoconazole and fluconazole, awaits final determination.     

The effect of limited exposure to antimycotics on the relative cell-surface hydrophobicity and the adhesion of oral Candida albicans to buccal epithelial cells

Candida albicans is the major aetiological agent of oral candidosis. Adhesion to oral mucosal surfaces is considered a prerequisite for its successful colonization and subsequent infection, and its relative cell-surface hydrophobicity (CSH) is a contributory physical force. Thus, the main aim here was to determine the CSH of 10 isolates of oral C. albicans after a short exposure to sublethal concentrations of four antifungal agents and to correlate these findings with their adhesion to human buccal epithelial cells (BEC). The yeasts were exposed to sublethal concentrations of nystatin [x 6 minimal inhibitory concentration (MIC)], 5-fluorocytosine (x 8 MIC), ketoconazole (x 4 MIC) and fluconazole (x 4 MIC) for 1 h. The drug was then removed, and the CSH and BEC adhesion assessed by a biphasic aqueous-hydrocarbon assay and a microscopic method, respectively. The mean percentage reductions of CSH after exposure to nystatin, 5-fluorocytosine, ketoconazole and fluconazole were 27.14% (p = 0.01), 9.46% (p = 0.43), 19.47% (p = 0.04) and 6.16% (p = 0.59). Similarly, exposure to all the drugs except 5-fluorocytosine resulted in a significant inhibition of yeast adhesion to BEC, with nystatin eliciting the highest and fluconazole the least inhibition. Further, on regression analysis a strong positive correlation was observed between CSH and adhesion to BEC after limited exposure to 5-fluorocytosine (r = 0.48, p < 0.0001), ketoconazole (r = 0.48, p < 0.0001), fluconazole (r = 0.55, p < 0.0001) as well as in the unexposed controls (r = 0.41, p = 0.001), although nystatin was an exception (r = 0.09, p = 0.44). Taken together, these data elucidate further mechanisms by which antimycotics may operate in vivo to suppress candidal pathogenicity.     

Extensive skin candidosis in an adult: effective treatment with itraconazole

A 34-year-old man with 6 years' untreated erythematous scaling of the skin was diagnosed as having extensive skin candidosis. Oral itraconazole was administered for 4 weeks (400 mg day-1 for the first 3 weeks and 200 mg day-1 for the last week). At the end of the 4-week treatment period, the rash was completely cleared from all skin sites, and Candida albicans was absent in culture tests on tissue samples. No adverse events were reported by the patient, and laboratory analysis revealed no abnormalities in the liver, kidney and haematological systems. Oral itraconazole is therefore an effective treatment for extensive skin candidosis.