Pathogenesis and treatment of oral candidosis

Recent mouse and rat methods for the study of experimental oral candidiasis

The Candida genus expresses virulence factors that, when combined with immunosuppression and other risk factors, can cause different manifestations of oral candidiasis. The treatment of mucosal infections caused by Candida and the elucidation of the disease process have proven challenging. Therefore, the study of experimentally induced oral candidiasis in rats and mice is useful to clarify the etiopathology of this condition, improve diagnosis, and search for new therapeutic options because the disease process in these animals is similar to that of human candidiasis lesions. Here, we describe and discuss new studies involving rat and mouse models of oral candidiasis with respect to methods for inducing experimental infection, methods for evaluating the development of experimental candidiasis, and new treatment strategies for oral candidiasis.

Effects of eating disorders on oral fungal diversity

BACKGROUND

The eating disorders anorexia and bulimia nervosa can cause several systemic and oral alterations related to poor nutrition and induced vomiting; however, the oral microflora of these patients is poorly studied.

OBJECTIVE

The aim of this study was to evaluate fungal microflora in the oral cavity of these patients by culture-dependent and culture-independent methods.

STUDY DESIGN

Oral rinse samples were cultured to assess the prevalence of Candida species, and the isolates were identified by API system. Microorganism counts were compared by the Mann-Whitney test (5%). Ribotyping, a type of molecular analysis, was performed by sequencing the D1/D2 regions of 28S rRNA.

RESULTS

Our results demonstrated that the eating disorder group showed higher oral Candida spp. prevalence with culture-dependent methods and higher species diversity with culture-independent methods.

CONCLUSIONS

Eating disorders can lead to an increased oral Candida carriage. Culture-independent identification found greater fungal diversity than culture-dependent methods.

Cell surface changes in the Candida albicans mitochondrial mutant goa1Δ are associated with reduced recognition by innate immune cells

We have previously characterized several fungal-specific proteins from the human pathogen Candida albicans that either encode subunits of mitochondria Complex I (CI) of the electron transport chain (ETC) or regulate CI activity (Goa1p). Herein, the role of energy production and cell wall gene expression is investigated in the mitochondria mutant goa1Δ. We show that downregulation of cell wall-encoding genes in the goa1Δ results in sensitivity to cell wall inhibitors such as Congo red and Calcofluor white, reduced phagocytosis by a macrophage cell line, reduced recognition by macrophage receptors, and decreased expression of cytokines such as IL-6, IL-10 and IFN-γ. In spite of the reduced recognition by macrophages, the goa1Δ is still killed to the same extent as control strains. We also demonstrate that expression of the epithelial cell receptors E-cadherin and EGFR is also reduced in the presence of goa1Δ. Together, our data demonstrate the importance of mitochondria in the expression of cell wall biomolecules and the interaction of C. albicans with innate immune and epithelial cells. Our underlying premise is thatmitochondrial proteins such as Goa1p and other fungal-specific mitochondrial proteins regulate critical functions in cell growth and in virulence. As such, they remain as valid drug targets for antifungal drug discovery.

Triterpenoid saponins from the aerial parts of Solidago virgaurea alpestris with inhibiting activity of Candida albicans yeast-hyphal conversion

As part of research for treatments to combat oral dryness, our evaluation of the activity of an aqueous extract of Solidago virgaurea (L.) ssp. alpestris (Asteraceae) revealed activity against Candida albicans hyphae, the pathogenic form of this yeast. Systematic bioassay-guided fractionation of this extract gave an active saponin-containing fraction from which six oleanane-type triterpenoid saponins were isolated. Three of these were isolated for the first time, as 3-O-(β-D-glucopyranosyl-(1→3)-β-D-glucopyranosyl)-28-O-(β-D-fucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl)-polygalacic acid (virgaureasaponin 4), 3-O-(β-D-glucopyranosyl)-28-O-(β-D-fucopyranosyl-(1→2)-α-L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2)-β-D-xylopyranosyl)-polygalacic acid (virgaureasaponin 5) and 3-O-(β-D-glucopyranosyl)-28-O-(α-L-rhamnopyranosyl-(1→3)-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2)-[5-O-acetylapiofuranosyl-(1→3)-[4-O-(3-(3-hydroxy-1-oxobutoxy)-1-oxobutyl)]-β-D-fucopyranosyl]-polygalacic acid (virgaureasaponin 6). Their structures were established by carrying out 1D and 2D NMR experiments along with HRMS analyses. All of the six saponins were evaluated to ascertain their inhibition of C. albicans yeast-hyphal conversion, and four of them showed significant inhibition.

Use of denaturing gradient gel electrophoresis for the identification of mixed oral yeasts in human saliva

A PCR-denaturing gradient gel electrophoresis (DGGE) method was established for the simultaneous presumptive identification of multiple yeast species commonly present in the oral cavity. Published primer sets targeting different regions of the Saccharomyces cerevisiae 26-28S rRNA gene (denoted primer sets N and U) and the 18S rRNA gene (primer set E) were evaluated with ten Candida and four non-Candida yeast species, and twenty Candida albicans isolates. Optimized PCR-DGGE conditions using primer set N were applied to presumptively identify, by band matching, yeasts in the saliva of 25 individuals. Identities were confirmed by DNA sequencing and compared with those using CHROMagar Candida culture. All primer sets yielded detectable DGGE bands for all species tested. Primer set N yielded mainly single bands and could distinguish all species examined, including differentiating Candida dubliniensis from C. albicans. Primer set U was less discriminatory among species but yielded multiple bands that distinguished subspecies groups within C. albicans. Primer set E gave poor yeast discrimination. DGGE analysis identified yeasts in 17 of the 25 saliva samples. Six saliva samples contained two yeast species: three contained C. albicans and three C. dubliniensis. C. dubliniensis was present alone in one saliva sample (total prevalence 16 %). CHROMagar culture detected yeasts in 16 of the yeast-containing saliva samples and did not enable identification of 7 yeast species identified by DGGE. In conclusion, DGGE identification of oral yeast species with primer set N is a relatively fast and reliable method for the simultaneous presumptive identification of mixed yeasts in oral saliva samples.

Oral antimicrobial rinse to reduce mycobacterial culture contamination among tuberculosis suspects in Uganda: a prospective study

RATIONALE

Contamination by bacterial or fungal organisms reduces the effectiveness of mycobacterial culture for diagnosis of pulmonary tuberculosis (TB). We evaluated the effect of an anti-microbial and an anti-fungal oral rinse prior to expectoration on culture-contamination rates.

METHODS

We enrolled a consecutive random sample of adults with cough for ≥ 2 weeks and suspected TB admitted to Mulago Hospital (Kampala, Uganda) between October 2008 and June 2009. We randomly assigned patients to oral rinse (60 seconds with chlorhexidine followed by 60 seconds with nystatin) vs. no oral rinse prior to initial sputum collection. Uganda National Tuberculosis Reference Laboratory technicians blinded to the method of sputum collection (with or without oral rinse) processed all sputum specimens for smear microscopy (direct Ziehl-Neelsen) and mycobacterial culture (Lowenstein-Jensen media).

RESULTS

Of 220 patients enrolled, 177 (80%) were HIV-seropositive (median CD4-count 37 cells/uL, IQR 13-171 cells/uL). Baseline characteristics were similar between patients in the oral-rinse (N = 110) and no oral-rinse (N = 110) groups. The proportion of contaminated cultures was significantly lower in the oral-rinse group compared to the no oral-rinse group (4% vs. 15%, risk difference -11%, 95% CI -18 to -3%, p = 0.005). Oral rinse significantly reduced the proportion of contaminated cultures among HIV-infected patients (3% vs. 18%, risk difference -14%, 95% CI -23 to -6%, p = 0.002) but not HIV-uninfected (6% vs. 4%, risk difference 2%, 95% CI -12 to +15%, p = 0.81) patients. However, the proportion of smear-positive specimens (25% vs. 35%, p = 0.10) and culture-positive specimens (48% vs. 56%, p = 0.24) were lower in the oral-rinse compared to the no oral-rinse group, although the differences were not statistically significant.

CONCLUSIONS

Oral rinse prior to sputum expectoration is a promising strategy to reduce mycobacterial culture contamination in areas with high HIV prevalence, if strategies can be devised to reduce the adverse impact of oral rinse on smear- and culture-positivity.

Antifungal activities of different extracts of marine macroalgae against dermatophytes and Candida species

Algae are bioactive natural resources, and due to the medical importance of superficial mycoses, we focused the action of macroalgae extracts against dermatophytes and Candida species. Seaweed obtained from the Riacho Doce beach, Alagoas (Brazil), were screened for the antifungal activity, through crude extracts using dichloromethane, chloroform, methanol, ethanol, water and chloroform and hexane fractions of green, brown and red algae in assays with standard strains of the dermatophytes Trichophyton rubrum, T. tonsurans, T. mentagrophytes, Microsporum canis, M. gypseum and yeasts Candida albicans, C. krusei, C. guilliermondi and C. parapsilosis. The M44-A and M27-A2/M38A manuals by CLSI were followed, and the minimum inhibitory concentration (MIC) ranged from 0.03 to 16.00 μg ml(-1), and an inhibition halo of 10.00-25.00 mm was observed for dermatophytes, while for yeast, it was from 8.00 to 16.00 μg ml(-1) and 10.00-15.00 mm. M. canis showed MIC of 0.03 μg ml(-1) and the largest inhibition halo in T. rubrum (25.00 mm) through the use of the methanol extract. For C. albicans, dichloromethane, methanol and ethanol extracts formed the largest inhibition halo. The ethanol extract was shown to be the best inhibiting fungi growth, and chloroform and hexane fractions of H. musciformis inhibited the growth of all dermatophytes and C. albicans, yielding the conclusion that apolar extracts obtained from algae presented the best activity against important pathogenic fungi.

The novel Candida albicans transporter Dur31 Is a multi-stage pathogenicity factor

Candida albicans is the most frequent cause of oral fungal infections. However, the exact pathogenicity mechanisms that this fungus employs are largely unknown and many of the genes expressed during oral infection are uncharacterized. In this study we sought to functionally characterize 12 previously unknown function genes associated with oral candidiasis. We generated homozygous knockout mutants for all 12 genes and analyzed their interaction with human oral epithelium in vitro. Eleven mutants caused significantly less epithelial damage and, of these, deletion of orf19.6656 (DUR31) elicited the strongest reduction in pathogenicity. Interestingly, DUR31 was not only involved in oral epithelial damage, but in multiple stages of candidiasis, including surviving attack by human neutrophils, endothelial damage and virulence in vivo. In silico analysis indicated that DUR31 encodes a sodium/substrate symporter with 13 transmembrane domains and no human homologue. We provide evidence that Dur31 transports histatin 5. This is one of the very first examples of microbial driven import of this highly cytotoxic antimicrobial peptide. Also, in contrast to wild type C. albicans, dur31Δ/Δ was unable to actively increase local environmental pH, suggesting that Dur31 lies in the extracellular alkalinization hyphal auto-induction pathway; and, indeed, DUR31 was required for morphogenesis. In agreement with this observation, dur31Δ/Δ was unable to assimilate the polyamine spermidine.

Influence of artificial saliva in biofilm formation of Candida albicans in vitro

Due to the increase in life expectancy, new treatments have emerged which, although palliative, provide individuals with a better quality of life. Artificial saliva is a solution that contains substances that moisten a dry mouth, thus mimicking the role of saliva in lubricating the oral cavity and controlling the existing normal oral microbiota. This study aimed to assess the influence of commercially available artificial saliva on biofilm formation by Candida albicans. Artificial saliva I consists of carboxymethylcellulose, while artificial saliva II is composed of glucose oxidase, lactoferrin, lysozyme and lactoperoxidase. A control group used sterile distilled water. Microorganisms from the oral cavity were transferred to Sabouraud Dextrose Agar and incubated at 37 °C for 24 hours. Colonies of Candida albicans were suspended in a sterile solution of NaCl 0.9%, and standardisation of the suspension to 106 cells/mL was achieved. The acrylic discs, immersed in artificial saliva and sterile distilled water, were placed in a 24-well plate containing 2 mL of Sabouraud Dextrose Broth plus 5% sucrose and 0.1 mL aliquot of the Candida albicans suspension. The plates were incubated at 37 °C for 5 days, the discs were washed in 2 mL of 0.9% NaCl and placed into a tube containing 10 mL of 0.9% NaCl. After decimal dilutions, aliquots of 0.1 mL were seeded on Sabouraud Dextrose Agar and incubated at 37 °C for 48 hours. Counts were reported as CFU/mL (Log10). A statistically significant reduction of 29.89% (1.45 CFU/mL) of Candida albicans was observed in saliva I when compared to saliva II (p = 0.002, considering p≤0.05).

One-pot synthesis of a new antifungal polymerisable monomer and its characterisation by coordination-ion spray mass spectrometry

We have investigated the synthesis of a new antifungal agent with a polymerisable moiety for the prevention of denture stomatisis. Nystatin (antifungal polyene) is modified in one step by reaction with isocyanatoethylmethacrylate to afford a new polymerisable antifungal agent in good yield (90%). In order to prove the monografting of the acrylate derivative and to localise the new group in the skeleton of the molecule, a rapid and efficient analytical method involving electrospray ionisation mass spectrometry (ESI-MS) was developed for the study. In view of the structures of such antifungal agents, their complexation with metal cations was investigated by Coordination-Ion Spray Mass Spectrometry (CIS-MS). This mass spectrometry study covers two aspects: improving the MS signal to overcome the low ionisation efficiency in ESI-MS and exploring the complexation behaviour of the induced structure to optimise the antifungal properties.

Pathogenesis and treatment of oral candidosis

Oral infections caused by yeast of the genus Candida and particularly Candida albicans (oral candidoses) have been recognised throughout recorded history. However, since the 1980s a clear surge of interest and associated research into these infections have occurred. This has largely been due to an increased incidence of oral candidosis over this period, primarily because of the escalation in HIV-infection and the AIDS epidemic. In addition, changes in medical practice leading to a greater use of invasive clinical procedures and a more widespread use of immunosuppressive therapies have also contributed to the problem. Whilst oral candidosis has previously been considered to be a disease mainly of the elderly and very young, its occurrence throughout the general population is now recognised. Candida are true ‘opportunistic pathogens’ and only instigate oral infection when there is an underlying predisposing condition in the host. Treatment of these infections has continued (and in some regards continues) to be problematic because of the potential toxicity of traditional antifungal agents against host cells. The problem has been compounded by the emergence of Candida species other than C. albicans that have inherent resistance against traditional antifungals. The aim of this review is to give the reader a contemporary overview of oral candidosis, the organisms involved, and the management strategies that are currently employed or could be utilised in the future.