Significance of modes of adherence in esophageal Candida albicans

A review of the ultrastructural features of superficial candidiasis

Commensal yeast Candida causes opportunistic infections ranging from superficial lesions to disseminated mycoses in compromised patients. Superficial candidiasis, the commonest form of candidal infections, primarily affects the mucosa and the skin where Candida lives as a commensal. Conversion of candidal commensalism into opportunism at the fungal-epithelial interface is still ill-defined. Nevertheless, fungal virulence mechanisms such as adhesion to epithelia, morphogenesis, production of secretory hydrolytic enzymes, and phenotypic switching are thought to contribute in the process of pathogenesis. On the other hand, host responses in terms of immunity and local epithelial responses are actively involved in resisting the fungal challenge at the advancing front of the infection. Ultrastructural investigations using electron microscopy along with immunohistochemistry, cytochemistry, etc. have helped better viewing of Candida-host interactions. Thus, studies on the ultrastructure of superficial candidiasis have revealed a number of fungal behaviors and associated host responses such as adhesion, morphogenesis (hyphae and appresoria formation), thigmotropism, production and distribution of extracellular enzymes, phagocytosis, and epithelial changes. The purpose of this review is to sum up most of the ultrastructural findings of Candida-host interactions and to delineate the important pathological processes underlying superficial candidiasis.

Experimental superficial candidiasis on tissue models

Candida species are common pathogens causing superficial mycoses primarily affecting the mucosa and the skin in humans. Crucial steps during pathogenesis of superficial candidiasis comprise fungal adhesion, colonisation and subsequent penetration of the respective tissues. Exploring these pathological events and perhaps fungal and tissue responses towards drug treatment is imperative in the management of this infection. Unfortunately, pathological biopsies of superficial candidiasis do not exhibit the early changes in the host-pathogen interaction as the tissues are already invaded by the fungi. In vivo experimental assessments of pathological processes of superficial candidiasis are also limited because of the difficulties in providing reproducible and comparable conditions in the host environment. Conversely, in vitro models have helped studying fungal-host interactions under more defined and controlled conditions. Some common in vitro models used to simulate superficial candidiasis are chick chorioallantoic membrane, mucosal explants and single layer or multiple layer cell cultures. Interestingly, these experimental approaches share advantages as well as disadvantages when compared with in vivo conditions. Hence, this review intends to discuss about the experimental superficial candidiasis produced in various tissue models and their advantages as well as disadvantages with a particular reference to further improvement of validity and reliability of such experiments.

A comparative study of candidal invasion in rabbit tongue mucosal explants and reconstituted human oral epithelium

The purpose of this study is to compare the light and scanning electron microscopic (SEM) features of tissue invasion by three Candida species (C. albicans, C. tropicalis, and C. dubliniensis) in two different tissue culture models: rabbit tongue mucosal explants (RTME) and reconstituted human oral epithelium (RHOE). Tongue mucosal biopsies of healthy New Zealand rabbits were maintained in explant culture using a transwell system. RHOE was obtained from Skinethic Laboratory (Nice, France). RTME and RHOE were inoculated with C. albicans, C. tropicalis, and C. dubliniensis separately and incubated at 37 degrees C, 5% CO(2), and 100% humidity up to 48 h. Light microscopic and SEM examinations of uninfected (controls) and infected tissues were performed at 24 and 48 h. C. albicans produced characteristic hallmarks of pathological tissue invasion in both tissue models over a period of 48 h. Hyphae penetrated through epithelial cells and intercellular gaps latter resembling thigmotropism. SEM showed cavitations on the epithelial cell surfaces particularly pronounced at sites of hyphal invasion. Some hyphae on RTME showed several clusters of blastospores attached in regular arrangements resembling "appareil sporifere". C. tropicalis and C. dubliniensis produced few hyphae mainly on RTME but they did not penetrate either model. Our findings indicate that multiple host-fungal interactions such as cavitations, thigmotropism, and morphogenesis take place during candidal tissue invasion. RTME described here appears to be useful in investigations of such pathogenic processes of Candida active at the epithelial front.

Alternative Candida albicans lifestyles: growth on surfaces

Candida albicans, an opportunistic fungal pathogen, causes a wide variety of human diseases such as oral thrush and disseminated candidiasis. Many aspects of C. albicans physiology have been studied during liquid growth, but in its natural environment, the gastrointestinal tract of a mammalian host, the organism associates with surfaces. Growth on a surface triggers several behaviors, such as biofilm formation, invasion, and thigmotropism, that are important for infection. Recent discoveries have identified factors that regulate these behaviors and revealed the importance of these behaviors for pathogenesis.

Prevalence of esophageal candidiasis among patients treated with inhaled fluticasone propionate

OBJECTIVES

Development of oropharyngeal candidiasis is a frequently reported adverse effect of inhaled corticosteroid use, but the prevalence of esophageal candidiasis is unknown. The aim of this study was to estimate the prevalence of esophageal candidiasis among patients treated with an inhaled corticosteroid, fluticasone propionate.

METHODS

Upper GI endoscopy was performed on 49 patients treated with inhaled fluticasone propionate to examine the prevalence of esophageal candidiasis. Of the patients, 36 had bronchial asthma and 13 had chronic obstructive pulmonary disease. To compare the prevalence with control patients, upper GI endoscopy was performed on 700 consecutive patients without malignancy or immunosuppression.

RESULTS

The prevalence of esophageal candidiasis was 37% among patients treated with inhaled fluticasone propionate, whereas only 0.3% of the control patients had the infection. The prevalence was especially high among patients with diabetes mellitus or those who were treated with a high dose of inhaled fluticasone propionate. Moreover, a reduction in the daily dose of inhaled fluticasone propionate eliminated the infection in four of five patients.

CONCLUSIONS

Esophageal candidiasis is a common complication of inhaled corticosteroid use.

An investigation of the association of the prothrombin G20210A gene mutation and inflammatory bowel disease: Factor II and IBD

BACKGROUND

A thrombotic etiology for inflammatory bowel disease (IBD) has been proposed as a result of its association with thromboembolic complications, smoking, the oral contraceptive pill, and the response of ulcerative colitis (UC) patients to heparin. We have previously demonstrated an increased prevalence of the Factor V Leiden mutation in UC and wished to investigate the frequency of the recently discovered prothrombin G20210A gene mutation in IBD. The aim of the study was to investigate the hypothesis that the prothrombic state associated with the prothrombin G20210A gene mutation is involved in the etiology of IBD.

PATIENTS AND METHODS

A prospective cohort study of patients attending the Bristol Royal Infirmary and Gloucestershire Royal Hospital's IBD clinics was performed. Thirty-nine patients with IBD (24 with Crohn's disease and 15 with UC) and 100 historical controls were screened for the presence of the prothrombin gene mutation using a heteroduplex-based polymerase chain reaction technique. None of the patients with IBD had a personal history of thromboembolism, while three of them had a family history.

RESULTS

No IBD patients had the prothrombin gene mutation compared with four (4%) controls (allelic frequency 2%).

CONCLUSION

There does not appear to be an association of the prothrombin gene mutation with IBD and therefore it is unlikely to be involved in the etiology of IBD.

[Orointestinal candidiasis with special emphasis on esophageal candidiasis]

Orointestinal mycoses are localized mainly in the oral cavity and in the oesophagus. Candida oesophagitis is not only found in AIDS-patients, also in patients of risk admitted to intensive care units. Upper intestinoscopies were made in 124 patients. Oesophageal candidosis was found in 6 patients, two of them had also Candida plaques in the stomach. The patients of the intensive care unit had an Apache-II-score of 26.7, those with Candida oesophagitis were 29.5. A significant increase in Candida antibodies was observed with 59 of 124 patients (47.6%), including all patients with oesophageal candidosis. Obviously also Candida infections of other localisations must be suspected. There was a correlation between the severity of endoscopic aspects and the invasiveness observed microscopically.

Esophageal Candida infection and adherence mechanisms in the nonimmunocompromised rabbit

Candida infection of the esophagus has been reported not only in immunocompromised hosts but also in healthy individuals. However, its mechanisms of action in healthy individuals have not been clarified. Our previous study suggested that physical contact was an important factor for the adherence of Candida albicans. The aim of the present study was to test our hypothesis and clarify the adherence mechanisms. Suspensions of Candida albicans cells were given to rabbits in drinking water without the use of immunosuppressive drugs and/or antibiotics, and the esophagus was examined. Candidial lesions were observed in 14 of 15 rabbits given the suspensions held in water with and without 30% sucrose for 13 days. The number of Candida albicans cells adhering to the esophagus per square millimeter by subepithelial cell insertion was significantly larger than that adhering by attachment. These results indicate that adherence of Candida albicans to the esophagus occurs by sustained physical contact alone under a nonimmunosuppressive state, and that subepithelial cell insertion results in greater attachment on adherence. Our findings provide a clue that may help clarify the mechanism of Candida infection in healthy individuals.