Cutaneous candidiasis is an opportunistic infection that arises, in most cases, from endogenous, saprophytic candidal blastospores that selectively colonize oral, gastrointestinal, vaginal, and cutaneous epithelium.
Yeasts are unicellular fungi that typically reproduce by budding.
Candidosis is an infection caused by the yeast
Superficial infections of skin and mucous membranes are the most common types of candidal infections of the skin [
Cutaneous candidiasis is an opportunistic infection that arises, in most cases, from endogenous, saprophytic
Under various environmental conditions,
Initial and prerequisite events in cutaneous candidiasis should, hypothetically, include colonization of epithelial surfaces with pathogenic species of
It has been well demonstrated that specific
This selective adherence is thought to contribute in part to predominance of
Most candidal species are known to produce virulence factors including protease factors.
The ability of the various yeast forms to adhere to the underlying epithelium is an important step in the production of hyphae and tissue penetration [
In cases in which the epithelial barrier or host immunity is impaired,
Initial events of cutaneous candidiasis include adherence of blastoconidia to epithelial cell surface, fungal proliferation and colonization, and invasion of epithelial tissue [
In vitro studies show that adherence to corneocytes [
In rodent models, it was shown that the same species are capable of hyphal invasion of corneocytes and stratum corneum to produce infection [
Non pathogenic species adhere poorly to corneocytes or mucosal cells [
Some studies concerning the infectivity and pathogenicity of
As an alternative to these models, other researchers used noninvasive methods obtaining separate corneocyte cells and used them as skin surface for
In order to characterize and compare initial adherence of
In the present study, we are reporting observations on the way
Normal thigh skin was harvested from skin surgically excised from women that underwent abdominoplasty. All specimens were prepared by putting pieces of skin, approximately 1 cm2, with full epidermal thickness into small (60 mm) petri dishes. The skin pieces were immersed in cold sterilized skin graft fluid (SGF) that was proved as adequate storage medium, which prolongs ex vivo skin viability for 2-3 weeks. Whenever possible, the skin was used within 1 h of its removal.
Skin graft fluid (SGF) at pH 6.4 was prepared using concentrated balanced salt solution 8.0 mL which is composed of NaCl 8.0 g/l, KCl 0.4 g/l, dibasic sodium phosphate 7H2O 0.0875 g/l, nonbasic potassium phosphate 0.0625 g/l, magnesium sulphate 7H2O 0.2 g/l, and dextrose anhydrous 1.0 g/l, all dissolved in H2O and sterilized, normal human plasma AB or A 20.0 mL and 0.5% neomycin sulphate in 72.0 mL of distilled water.
The criteria for determining the viability of the skin were based on histological tests detailed by Peled et al. [
Fifty microliter of each fungal strain were spread equally over the skin surface (stratum corneum). The samples were incubated for 1 day to 5 days, at 30°C. The storage medium (SGF) was changed daily. Two different concentrations of blastoconidia,104 mL−1(low) and 106 mL−1 (high) in triplicates were used. The inoculum was prepared from a plate containing Sabouraud medium and incubated for 48 hours. Thereafter the proper concentrations were estimated by viable counting.
Controls: skin sections without
Scanning electron microscopy was used for examining the inoculated skin specimens.
specimens were fixed overnight in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer (pH 7.2) at 4°C, rinsed three times with PBS; and postfixed with 2% osmium tetraoxide for 2 h. Samples were then dehydrated in graded concentrations of ethanol (25–100%) and air-dried. The samples were viewed on an HR-SEM, ultraplus, Carl Zeiss SMT, Gemini.
Clinical isolates of
SEM of
1 day 104 mL−1
1 day 106 mL−1
5 days 104 mL−1
5 days 106 mL−1
5 days 106 mL−1
5 days 106 mL−1
The material had a strand-like appearance (in past studies “cohesion”) (Figures
Pseudohyphae elements are observed after 1 day and after 5 days (Figures
After 5 days, huge amounts of blastoconidia are shown, covering almost the entire skin model, and the blastoconidia are embedded in a layer that resembles biofilm (Figures
Low amounts of blastoconidia are observed with
SEM of
1 day 104 mL−1
1 day 106 mL−1
5 days 104 mL−1
5 days 106 mL−1
5 days 106 mL−1
5 days 106 mL−1
After 5 days at the higher concentrations the blastoconidia were coated with the material linking adjacent blastoconidia (Figures
Pseudohyphae are observed after 1 day at the higher concentration and also after 5 days (Figures
After 1 day at low and high concentrations, only few blastoconidia were observed (Figures
SEM of
1 day 104 mL−1
1 day 106 mL−1
5 days 104 mL−1
5 days 106 mL−1
After 5 days of incubation, more blastoconidia adhered in both concentrations, some kind of “threads” are shown, and the cells are embedded in the surface layer (Figures
After 1 day we were able to see characteristics that resemble minimal biofilm formation in all
After 1 day and after 5 days we observed normal epidermis (Figures
SEM of control skin. SEM of normal skin after 1 day and 5 days ((a), (b)). The skin without treatment served as control. The skin is well preserved.
1 day
5 days
In this study on the human skin ex vivo model, we demonstrated that
Adhesion is provided partially by mucopolysaccharide molecules and can be evaluated qualitatively by microscopic examination of interactions between the yeast and the epithelium or quantitatively by measuring the specific adhesion of
In experimental rodent cutaneous candidiasis using
In concordance with past studies, the present study ultrastructural visualization of adherence demonstrated amorphous material coating blastoconidia, mainly of
In those past studies this material was called cohesin. This cohesin was found as a film of loosely adherent strandlike material on the corneocyte surface of newborn mouse skin, in association with adherent blastoconidia, and was seen only with
In our study, all