Comparison of Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosis adhesive properties and pathogenicity

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Abstract

Retrospective studies indicate that Candida metapsilosis and Candida orthopsilosis each represents 1–10% of the infections/colonisations attributed to C. parapsilosis by conventional biochemical tests. Little is known on the virulence properties of these fungi and on their role in the establishment/progression of the infection. In this study, the adhesive properties of clinical isolates belonging to the ‘psilosis’ species were assessed in an in vitro model of co-incubation with human buccal epithelial cells (HBECs). Ectophosphatase activity was also measured for all isolates, since the activity of this enzyme has previously been linked to adhesion properties in C. parapsilosis. The results indicate that whilst C. parapsilosis and C. orthopsilosis strains showed similar adhesion abilities, C. metapsilosis isolates displayed a significantly lower ability to adhere to HBECs (P < 0.05). No evidence of a correlation between ectophosphatase activity and adhesion was observed, and this finding was also confirmed by phosphatase inhibition experiments. Experimental vaginal candidiasis induced in oestrogen-treated mice with representative isolates of the 3 species indicated that mice infected with C. metapsilosis displayed a reduced vaginal fungal burden, especially in the early stages of the infection. The overall findings confirm that C. orthopsilosis has a comparable behaviour to C. parapsilosis, whilst C. metapsilosis seems to possess a reduced virulence potential.

Introduction

Candida parapsilosis, C. metapsilosis, and C. orthopsilosis have been the subject of a growing number of epidemiological investigations, aimed at better defining their prevalence and drug susceptibility to commonly used antifungals. Retrospective analysis based on DNA analysis indicates that C. metapsilosis and C. orthopsilosis each represents 1–10% of the infections/colonisations attributed to C. parapsilosis by conventional biochemical tests (Lockhart et al., 2008, Tavanti et al., 2007, Hensgens et al., 2009, Bonfietti et al., 2012, Romeo et al., 2012). Routine identification of the 3 species would significantly speed up prevalence studies and improve our understanding of the epidemiology of the psilosis complex. In this respect, high throughput approaches such as Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) have emerged as powerful and rapid tools for the discrimination of members of the C. parapsilosis species complex (Carbonnelle et al., 2011, Pinto et al., 2012). However, their role in replacing conventional identification of yeast is not yet fully established.

To date, C. parapsilosis is the only species of the complex for which a commensal status has been demonstrated in humans (Lupetti et al., 2002, Bonassoli et al., 2005), although a metagenomic approach showed the presence of C. metapsilosis in the oral cavity of healthy human subjects (Ghannoum et al., 2010).

Few studies are available on virulence traits for C. orthopsilosis and C. metapsilosis, among these, a pioneer study performed by Gácser et al. (2007) evaluated the invasive properties of the C. parapsilosis complex in a reconstituted human oral epithelium. C. metapsilosis was the least invasive species, while C. orthopsilosis and C. parapsilosis were able to colonize and invade the epithelial tissue to a similar extent. C. parapsilosis infections have often been associated with the use of indwelling catheters and its ability to produce biofilm on prosthetic materials (Trofa et al., 2008). The biofilm-forming ability on silicone elastomer discs by the psilosis group species has been thoroughly investigated by the Ghannoum group, indicating that C. parapsilosis, C. orthopsilosis, and C. metapsilosis isolates are able to form biofilm with similar biomass and structure (Lattif et al., 2010) even though in our hands, C. parapsilosis clinical isolates resulted the more prolific biofilm producers (Tavanti et al., 2005, Tavanti et al., 2007, Tavanti et al., 2010, Hensgens et al., 2009). While data on proteolytic and lypolytic activities of C. parapsilosis are available (Tavanti et al., 2010, Trofa et al., 2011, Horváth et al., 2012), little or no evidence is provided for the 2 other species (Hensgens et al., 2009). In addition, the pathogenic potential of isolates belonging to the 3 species has been evaluated in an in vitro infection model of microglial cells with C. metapsilosis behaving as the least virulent member of the group. Indeed, C. metapsilosis caused little or no damage to microglial cells as opposed to what was observed for C. parapsilosis and C. orthopsilosis-infected cells (Orsi et al., 2010).

In this study, the adhesive properties of reference and clinical isolates belonging to the 3 species were assessed in an in vitro model of adhesion to human buccal epithelial cells. Since phosphatase activity has previously been linked to adhesion in C. parapsilosis (Fernanado et al., 1999, Kiffer-Moreira et al., 2007), we evaluated the role that this enzyme plays in the adhesion process by irreversibly inhibiting the enzymatic activity prior to the adhesion assay. The pathogenic potential of C. parapsilosis, C. metapsilosis, and C. orthopsilosis was also compared in an in vivo model of murine vaginal candidiasis.

Section snippets

Isolates

The isolates used in this study are part of a strain collection deposited at the Department of Biology, University of Pisa. Isolates were originally identified as C. parapsilosis according to their biochemical profile on API32 ID and a Vitek 2-advanced colorimetric semi-automated system (bioMérieux, Marcy l’Etoile, France). Molecular identification of C. metapsilosis and C. orthopsilosis was performed as previously described (Tavanti et al., 2005, Tavanti et al., 2007). Briefly, BanI digestion

Adhesion of C. parapsilosis, C. orthopsilosis, C. metapsilosis to human buccal epithelial cells

The adhesive properties of 3 reference strains and a total of 30 clinical isolates of C. parapsilosis, C. orthopsilosis, and C. metapsilosis to HBECs were assessed following a 45 min co-incubation at 37 °C. As shown in Table 1, the adherence ability varied within each species with values ranging from 314 ± 57 to 3577 ± 108 yeast/100 HBECs for C. parapsilosis, from 64 ± 14 to 2645 ± 645 yeast/100 HBECs for C. orthopsilosis, and from 39 ± 22 to 970 ± 378 yeast/100 HBECs for C. metapsilosis isolates. The mean

Discussion

A growing number of studies points to the fact that Candida orthopsilosis and C. metapsilosis circulate in clinical settings, although to a minor extent, and are able to cause superficial as well as systemic infections (Lockhart et al., 2008, Romeo et al., 2012, Feng et al., 2012). C. parapsilosis is the most frequent and better studied species of the complex; it is recognised to be a human skin commensal (Bonassoli et al., 2005, Trofa et al., 2008), and its clinical relevance is on the rise as

Conflict of interest statement

The authors declare that there are no conflicts of interest.

Acknowledgements

This work was supported by the Italian “Ministero dell’Istruzione, dell’Università e della Ricerca”, FIRB research grant number RBFR100FLV.

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