Increased adherence of fluconazole-resistant isolates of Candida species to explanted esophageal mucosa

The resistance to fluconazole in patients with esophageal candidiasis

CONTEXT

Esophageal candidiasis is often observed in patients with risk factors for its development and fluconazole is the therapeutic choice for the treatment of this disease.

OBJECTIVES

To determine its frequency, by performing upper digestive endoscopy; to determine Candida species involved in its pathogenesis and verify their distribution according with the predisposing factors and to determine susceptibility to fluconazole in the samples.

METHODS

From March 2006 to April 2007, all patients submitted to esophagogastroduodenoscopy at the Digestive Endoscopy Unit in the Oswaldo Cruz University Hospital, Recife, PE, Brazil, were eligible for the study. Samples were collected from patients who presented lesions consistent with esophageal candidiasis in order to identify Candida species and verify their susceptibility to fluconazole. The predisposing factors for the occurrence of esophageal candidiasis were described.

RESULTS

Of 2,672 patients referred to upper endoscopy at the Digestive Endoscopy Unit, 40 (1.5%) had endoscopic findings compatible with esophageal candidiasis. The average age was 49.1 years. Twenty one patients (52.5%) were less than 50 years old, of which 82.6% were infected with HIV. Most of them (52.5%) were males and 65.0% were inpatients. Diseases were identified in 90% of the patients and 21 (52.5%) were HIV positive. Concerning endoscopic findings, severe forms of esophagitis were found in 50% of the patients with CD4 count <200. Non-albicans Candida species were isolated in 22.7% of HIV positive and in 45% HIV negative patients. A total of 6 (14.28%) samples were resistant to fluconazole, while 2 (4.76%) samples had dose depending susceptibility to this drug.

CONCLUSIONS

Esophageal candidiasis prevalence was low, although within the results described by other authors. Male and inpatients were the most affected. The species isolated varied according to the characteristics of each group studied. Both, resistance and dose-depending susceptibility to fluconazole were considered high.

Oral candidiasis-adhesion of non-albicans Candida species

Oral candidiasis is an opportunistic infection caused primarily by Candida albicans. However, in recent years, species of non-albicans Candida have been implicated more frequently in mucosal infection. Candida species usually reside as commensal organisms and are part of normal oral microflora. Determining exactly how transformation from commensal to pathogen takes place and how it can be prevented is continuous challenge for clinical doctors. Candidal adherence to mucosal surfaces is considered as a critical initial step in the pathogenesis of oral candidiasis. Acrylic dentures, acting as reservoirs, play an important role in increasing the risk from Candida colonisation. Thus, this review discusses what is currently known about the adhesion of non-albicans Candida species of oral origin to buccal epithelial cells and denture acrylics.

Evaluation of adhesion to buccal epithelial cells in Candida species obtained from denture wearers after exposure to fluconazole

The aim of this study was to assess the adhesion ability by Candida spp. obtained from denture wearer patients with and without denture stomatitis and the possible reduction in adhesion after exposure to fluconazole. Nine C. tropicalis, five C. glabrata and two C. parapsilosis obtained from the oral cavity of patients with denture stomatitis and 11 C. tropicalis, nine C. glabrata and six C. parapsilosis obtained from the oral cavity of denture wearers with normal palatal mucosa were compared for adhesion ability to buccal epithelial cells (BEC) and reduction in adhesion after exposure to fluconazole. Candida spp. obtained from denture stomatitis patients were more adherent to BEC, and there was a reduction in adhesion after exposure to fluconazole in all the species tested. Our results demonstrated that exposure to fluconazole reduces Candida spp. adherence to BEC. These results also suggest that adhesion, even in non-albicans species, could be factors that, along with predisposing conditions related to the host, determine if an individual will develop disease or remain as a healthy carrier and confirm that fluconazole has an impact in the adherence ability in Candida spp.

Oral candidosis in patients with removable dentures

The prevalence of Candida species with and without denture-related stomatitis were evaluated in 167 Jordanian patients. The study revealed that 47 (28%) of the patients with denture-related stomatitis were colonized with Candida species (clinical group). Candida albicans was responsible for most cases of denture-related stomatitis (72%), and it was the only species capable of secreting aspartic proteinases. The study also indicated that candidal colonization was not influenced by predisposing haematological deficiencies, as both the clinical and control patient groups showed comparable haematological parameters and the differences were not significant (P > 0.05). All Candida species isolates were 100% susceptible to amphotericin B, while these isolates were less susceptible (25-75%) to fluconazole.

Antifungal drug resistance of pathogenic fungi

Pathogenic fungi have many complex mechanisms of resistance to antifungal drugs. Information about the clinical, cellular, and molecular factors contributing to antifungal-drug resistance continues to accumulate. We critically review the diagnosis, epidemiology, and mechanisms of antifungal drug resistance of pathogenic fungi. Better understanding of this resistance should assist in developing better detection strategies for preventing and treating refractory mycoses in the future.

Gene regulation and host adaptation mechanisms in Candida albicans

The yeast Candida albicans is a harmless member of the normal microflora on the mucosal surfaces of most healthy persons, but it can cause severe opportunistic infections in immunosuppressed patients. To become a successful human commensal and pathogen, C. albicans has evolved host adaptation mechanisms on different levels. The regulated expression of virulence and other genes in response to environmental signals allows an optimal adaptation to new host niches during the course of an infection. In addition, C. albicans is able to switch between different cell types in a reversible and apparently random fashion. Phenotypic switching involves the coordinated regulation of phase-specific genes, and the resulting generation of selected, pre-programmed cell types may represent an additional strategy to adapt to certain host environments. Finally, C. albicans produces genetically altered variants at a high rate. This microevolution ensures survival when the pathogen encounters new adverse conditions, as exemplified by the development of stable drug-resistant variants under the selection pressure caused by antimycotic therapy. Thus, rather than the possession of single dominant virulence factors, it is its remarkable versatility that makes C. albicans the most important fungal pathogen of humans.