[Investigations on the regulation of secreted aspartyl proteases in a model of oral candidiasis in vivo]

[Opportunistic mycoses of ENT organs. Part 1]

The present literature review summarizes information about the diseases of the upper respiratory tract and the ears caused by opportunistic fungi. The factors responsible for the increased frequency of opportunistic infections, among which mycosis is the leading one, are given. The exogenous and endogenous risk factors are described. The main pathogens of opportunistic mycotic infections of the ENT-organs are listed. Special attention is given to the mechanism underlying the development of anti-colonial immunity of the upper respiratory tract and the ears and the formation of the antifungal immunity of the macroorganism as a whole. The data on the pathogenetic factors of mycelial and yeast-like micromycetes are presented. The main variants of the pathogenetic mechanisms, such as adhesion, invasive growth, and penetration, behind the formation of the mycotic lesions are considered. These biological properties of the fungi contribute to their ability to cause a wide range of pathological changes - from the superficial lesions of the skin and mucous membranes of the ENT organs to the deep invasive processes. The protective cellular and humoral immune reactions of a macroorganism that develop in response to the introduction of a pathogenic fungus are described. The review lists the main nosological forms of mycosis known to affect the ENT-organs with special reference to the leading role of the yeast-like fungi belonging to the genus Candida in the development of mycotic lesions of these biotopes (64.65%). The most pathogenic species, Candida albicans, prevails in the structure of the yeast-like fungi biome whereas the leading role in the development of mycosis of the ENT organs by micromycetes of mold belongs to the species Aspergillus niger.

Extracellular proteinases of Candida species pathogenic yeasts

The increased incidence of severe disseminated infections caused by the opportunistic yeast-like fungi Candida spp. highlights the urgent need for research into the major virulence factors of these pathogens-extracellular aspartic proteinases of the candidapepsin and yapsin families. Classically, these enzymes were considered to be generally destructive factors that damage host tissues and provide nutrients for pathogen propagation. However, in recent decades, novel and more specific functions have been suggested for extracellular candidal proteinases. These include contributions to cell wall maintenance and remodeling, the formation of polymicrobial biofilms, adhesion to external protective barriers of the host, the deregulation of host proteolytic cascades (such as the complement system, blood coagulation and the kallikrein-kinin system), a dysregulated host proteinase-inhibitor balance, the inactivation of host antimicrobial peptides, evasion of immune responses and the induction of inflammatory mediator release from host cells. Only a few of these activities recognized in Candida albicans candidapepsins have been also confirmed in other Candida species, and characterization of Candida glabrata yapsins remains limited.

Lower filamentation rates of Candida dubliniensis contribute to its lower virulence in comparison with Candida albicans

Candida albicans and C. dubliniensis are very closely related yeast species. In this study, we have conducted a thorough comparison of the ability of the two species to produce hyphae and their virulence in two infection models. Under all induction conditions tested C. albicans consistently produced hyphae more efficiently than C. dubliniensis. In the oral reconstituted human epithelial model, C. dubliniensis isolates grew exclusively in the yeast form, while the C. albicans strains produced abundant hyphae that invaded and caused significant damage to the epithelial tissue. In the oral-intragastric infant mouse infection model, C. dubliniensis strains were more rapidly cleared from the gastrointestinal tract than C. albicans. Immunosuppression of Candida-infected mice caused dissemination to internal organs by both species, but C. albicans was found to be far more effective at dissemination than C. dubliniensis. These data suggest that a major reason for the comparatively low virulence of C. dubliniensis is its lower capacity to produce hyphae.

Temporal expression of the Candida albicans genes CHK1 and CSSK1, adherence, and morphogenesis in a model of reconstituted human esophageal epithelial candidiasis

We previously demonstrated that genes encoding a putative two-component histidine kinase (CHK1) or a response regulator (CSSK1) are each required for virulence in a murine model of hematogenously disseminated candidiasis and that strains with each gene deleted are also defective in morphogenesis under certain growth conditions. In the present study, the role of these two genes in the adherence to and colonization of reconstituted human esophageal tissue (RHE) is described. We compared strains of Candida albicans with deletions of chk1 (strain CHK21) and cssk1 (strain CSSK21) to wild-type cells (CAF2), as well as strains with CHK1 and CSSK1 reconstituted (strains CHK23 and CSSK23, respectively). Adherence and colonization of RHE were evaluated in periodic acid-Schiff-stained sections, as well as by SEM. We observed that both deletion-containing strains colonized the RHE to a lesser extent than did CAF2 and that the percent germination by both strains was reduced in comparison to that of control strains at 1 h postinfection. Expression of CHK1 or CSSK1 was quantitated by reverse transcription (RT)-PCR from RHE tissues infected with wild-type C. albicans yeast cells. Expression of both CHK1 and CSSK1 increased over the 48-h period following infection of the tissue, although expression of CHK1 was greater than that of CSSK1. By RT-PCR, we have also shown that expression of CHK1 and CSSK1 in the strains with cssk1 and chk1 deleted, respectively, was similar to that of CAF2, indicating that CHK1 and CSSK1 do not regulate each other but probably encode signal proteins of different pathways. Our observations indicate that CHK1 and CSSK1 are each partially required for colonization and conversion to filamentous growth on RHE tissue.