Adherence to polystyrene of clinically relevant isolates of Candida species

Virulence properties and sensitivity profile of Candida parapsilosis complex species and Kodamaea ohmeri isolates from onychomycosis of HIV/AIDS patients

Cutaneous fungal infections include onychomycosis, an infection of the nail that affects both healthy and immunocompromised patients. This study investigated the in vitro hydrolytic enzymes production, adhesion and biofilm formation capacity of Candida parapsilosis complex species and Kodamaea ohmeri isolates from onychomycoses of HIV/AIDS patients and also established the antifungal sensitivity profiles of these isolates. Onychomycosis in HIV/AIDS patients showed a high prevalence of emerging yeasts, among which C. parapsilosis complex species and K. ohmeri were the most frequent. Three C. parapsilosis sensu stricto and two C. orthopsilosis isolates were resistant to amphotericin B and 83% of isolates were resistant to terbinafine. All three different species evaluated were proteinase and hemolysin producers. All isolates adhered to stainless steel and siliconized latex surfaces, and carbohydrates intensified adhesion of all isolates. Isolates adhered to keratinous nail and 50% formed biofilms with strong intensity. In multispecies or polymicrobial biofilms, C. albicans and Staphylococcus aureus regulated the biofilm formation of the analyzed species, decreasing the number of their cells in biofilms. The isolation of emerging yeast species from onychomycosis which are great producers of hydrolytic enzymes and with high adhesion and biofilm formation capacity is a result that should be considered relevant in clinical practice. In addition, half of the isolates was resistant to at least one of the tested antifungals. Taken together these data corroborate the infectious capacity and viability of these isolates under favorable conditions.

Interspecies variation in Candida biofilm formation studied using the Calgary biofilm device

An in vitro assay to study multiple Candida biofilms, in parallel, has been carried out using the Calgary biofilm device (CBD). We here report: i) standardization of the CBD for Candida albicans biofilm formation, ii) kinetics of C. albicans biofilm formation, iii) biofilm formation by five Candida species, and iv) effect of dietary carbohydrates on biofilm formation. The biofilm metabolic activity on all CBD pegs was similar (p=0.6693) and C. albicans biofilm formation revealed slow growth up to 36 h and significantly higher growth up to 48 h (p<0.001). Significant differences in total biofilm metabolic activity were seen for glucose, fructose and lactose grown C. albicans compared with sucrose and maltose grown yeasts. Candida krusei developed the largest biofilm mass (p<0.05) relative to C. albicans, C. glabrata, C. dubliniensis and C. tropicalis. Scanning electron microscopy revealed that C. krusei produced a thick multilayered biofilm of pseudohyphal forms embedded within the polymer matrix, whereas C. albicans, C. dubliniensis and C. tropicalis biofilms consisted of clusters or chains of cells with sparse extracellular matrix material. We conclude that CBD is a useful, simple, low cost miniature device for parallel study of Candida biofilms and factors modulating this phenomenon.

Comparison of adherence of Candida albicans and Candida parapsilosis to silicone catheters in vitro and in vivo

OBJECTIVE

Although Candida parapsilosis has been associated with device-related infections in the clinical settings, factors that contribute to this association have not been previously examined. The objectives of this study were to compare in vitro and in vivo the adherence to silicone catheters of: (1) Candida albicans vs. C. parapsilosis, and (2) invasive vs. colonizing isolates of C. albicans and C. parapsilosis.

METHODS

The records of 840 patients who had had Candida species isolated at three teaching hospitals during a three-month period were reviewed. A total of 20 clinical isolates of each of C. parapsilosis and C. albicans were examined for their adherence to silicone catheters in vitro and in a rabbit model of percutaneously placed catheters. For each Candida species, ten invasive isolates that had caused clinical device-related infection and 10 colonizing isolates that had caused only device colonization were studied.

RESULTS

Candida parapsilosis accounted for <5% of yeast isolates from all sites, while three-quarters were C. albicans. Candida parapsilosis was isolated proportionately more often from blood and/or devices than C. albicans (34.3% vs. 8.5%, respectively, P < 0.0001). There were no significant differences in the degrees of adherence in vitro and in vivo between C. albicans and C. parapsilosis or between invasive and colonizing Candida.

CONCLUSION

Although C. parapsilosis was isolated proportionately more often from blood and/or devices than C. albicans in our studied population, there was no significant difference in the adherence of the two Candida species to silicone, nor between invasive and colonizing Candida in our in vitro and in vivo models. Factors other than microbial adherence may help explain the observed association of C. parapsilosis with device-related infections.

Candida biofilms

In response to attachment to a surface, fungal cells produce biofilms, three-dimensional structures composed of cells surrounded by exopolymeric matrices. Surface attachment causes Candida albicans cells to enter a special physiological state in which they are highly resistant to antifungal drugs and express the drug efflux determinants CDR1, CDR2 and MDR1. C. albicans biofilms produced under different conditions differ in their cellular morphology and matrix content, which suggests that biofilms formed within a host, for example on indwelling medical devices, would also differ depending on the nature of the device and its location. The mechanisms by which surface attachment leads to biofilm formation are presently not understood.