Carlos Alves

Interactions of Candida albicans with host epithelial surfaces

Candida albicans is an opportunistic, fungal pathogen of humans that frequently causes superficial infections of oral and vaginal mucosal surfaces of debilitated and susceptible individuals. The organism is however, commonly encountered as a commensal in healthy individuals where it is a component of the normal microflora. The key determinant in the type of relationship that Candida has with its host is how it interacts with the epithelial surface it colonises. A delicate balance clearly exists between the potentially damaging effects of Candida virulence factors and the nature of the immune response elicited by the host. Frequently, it is changes in host factors that lead to Candida seemingly changing from a commensal to pathogenic existence. However, given the often reported heterogeneity in morphological and biochemical factors that exist between Candida species and indeed strains of C. albicans, it may also be the fact that colonising strains differ in the way they exploit resources to allow persistence at mucosal surfaces and as a consequence this too may affect the way Candida interacts with epithelial cells. The aim of this review is to provide an overview of some of the possible interactions that may occur between C. albicans and host epithelial surfaces that may in turn dictate whether Candida removal, its commensal persistence or infection follows.

Vulvovaginal candidiasis: Epidemiology, microbiology and risk factors

Abstract Vulvovaginal candidiasis (VVC) is an infection caused by Candida species that affects millions of women every year. Although Candida albicans is the main cause of VVC, the identification of non-Candida albicans Candida (NCAC) species, especially Candida glabrata, as the cause of this infection, appears to be increasing. The development of VVC is usually attributed to the disturbance of the balance between Candida vaginal colonization and host environment by physiological or nonphysiological changes. Several host-related and behavioral risk factors have been proposed as predisposing factors for VVC. Host-related factors include pregnancy, hormone replacement, uncontrolled diabetes, immunosuppression, antibiotics, glucocorticoids use and genetic predispositions. Behavioral risk factors include use of oral contraceptives, intrauterine device, spermicides and condoms and some habits of hygiene, clothing and sexual practices. Despite a growing list of recognized risk factors, much remains to be elucidated as the role of host versus microorganisms, in inducing VVC and its recurrence. Thus, this review provides information about the current state of knowledge on the risk factors that predispose to VVC, also including a revision of the epidemiology and microbiology of VVC, as well as of Candida virulence factors associated with vaginal pathogenicity.

Candida albicans promotes invasion and colonisation of Candida glabrata in a reconstituted human vaginal epithelium

OBJECTIVEnThe principal aim of this study was to investigate the inxa0vitro co-infection of a reconstituted human vaginal epithelium (RHVE) by Candida albicans and Candida glabrata.nnnMETHODSnThe ability of both species to invade and colonise the RHVE was examined using species-specific peptide nucleic acid (PNA) probe hybridisation, confocal laser scanning microscopy (CLSM) and a novel qRT-PCR protocol for Candida quantification in the tissues. RHVE damage was evaluated by measuring lactate dehydrogenase (LDH) activity. Candida virulence gene expression (HWP1, ALS, EPA, PLB, PLD and SAP) was evaluated by quantitative RT-PCR.nnnRESULTSnThe results showed that whilst both species induced damage to the RHVE, this was notably less with C. glabrata. Interestingly, there was a significant increase in C. glabrata RHVE colonisation and invasiveness when it was added to the tissue with C. albicans. The extent of RHVE damage caused by the two species appeared to be primarily dependent on the process of invasion. Of the virulence genes assayed, HWP1, PLD1 and ALS3 were deemed to be most associated with pathogenicity in the model.nnnCONCLUSIONSnFor the first time, we have demonstrated that the RHVE model coupled with specific tools of analysis, allows assessment of Candida colonisation and invasion in single and co-infection. Using this model we have demonstrated that C. albicans enhanced C. glabrata colonisation, invasion and tissue damage, which was also evidenced by the expression of virulence genes.

Antifungal activity of phenolic compounds identified in flowers from North Eastern Portugal against Candida species

AIMnTo evaluate the antifungal effect of gallic acid, catechin, luteolin and quercetin, phenolic compounds identified from flowers of North Eastern Portugal, against Candida planktonic and biofilm cells.nnnMATERIALS & METHODSnThe MICs were determined in Candida planktonic cells and the effect of phenolic compounds on Candida biofilms was assessed through quantification of colony-forming units.nnnRESULTSnMIC values demonstrated that gallic acid presented the highest effect against all Candida species. Catechin showed a similar effect against Candida albicans American Type Culture Collection (ATCC) 90028 cells. In addition, gallic acid and quercetin had demonstrated only a minimal effect against Candida species biofilms.nnnCONCLUSIONnGallic acid affected the growth of the different planktonic Candida species in all concentrations used; still, catechin showed a similar effect against C. albicans ATCC 90028 and Candida glabrata ATCC 2001 cells. In addition, only gallic acid and quercetin demonstrated a slight effect against all Candida species biofilms.

Effects of fluconazole on Candida glabrata biofilms and its relationship with ABC transporter gene expression.

Candida glabrata has emerged as the second most prevalent fungal pathogen and its ability to form biofilms has been considered one of the most important virulence factors, since biofilms present a high tolerance to antifungal agents used in fungal infection treatment. The mechanisms of biofilm tolerance to antifungal agents remain poorly understood. Thus, the aim of this study was to evaluate the effects of fluconazole (FLU) on the formation and control of C. glabrata biofilms and its relation with the expression of genes encoding for ABC transporters, CDR1, SNQ2, and PDR1. For that, minimal inhibitory concentration values for seven C. glabrata strains were determined and the effect of FLU against C. glabrata biofilms was evaluated by total biomass quantification and viable cell enumeration. Matrices from biofilms were analyzed in terms of protein, carbohydrate and DNA content. ABC transporter gene expression was analyzed for quantitative real-time PCR. In addition to the high amounts of proteins and carbohydrates detected in the extracellular matrices in the presence of FLU, this work showed that the overexpression of efflux pumps is a possible mechanism of biofilm tolerance to FLU and this phenomenon alters the structure of C. glabrata biofilms by creating cell clusters.

Effect of progesterone on candida albicans vaginal pathogenicity

Candida albicans is responsible for the majority of cases of vulvovaginal candidiasis (VVC), an infection which occurs mainly during the luteal phase of the menstrual cycle or during the pregnancy, when levels of progesterone are elevated. One of the most important candidal virulence factors is the ability to adhere to host surfaces and form biofilms. The aim of this study was to determine the influence of progesterone on C. albicans virulence, namely biofilm formation and colonisation/invasion of a reconstituted human vaginal epithelium (RHVE). Biofilm formation on the RHVE was evaluated by enumeration of culturable cells, total mass quantification and scanning electron microscopy. The capacity of C. albicans strains to invade and colonise the tissue was examined by fluorescence microscopy using species-specific peptide nucleic acid (PNA) probe hybridisation, and quantitatively evaluated by RT-PCR Candida quantification methodology. Furthermore, gene (BCR1 and HWP1) expression of biofilm and RHVE-colonising cells was evaluated by quantitative RT-PCR. Results confirmed that progesterone reduced the capacity of C. albicans strains to form biofilms and to colonise and invade RHVE. Additionally, it was demonstrated that progesterone decreased expression of BCR1 and HWP1, which are important virulence determinants of C. albicans. In conclusion, it was evident that progesterone can have a major influence on C. albicans pathogenicity on vaginal epithelial cells and may partly explain susceptibility of women to VVC at different stages of the menstrual cycle.

Decay effects of pollutants on stony materials in the built environment

This review discuss the effects that pollutants have on stony materials applied on the built environment, illustrating different macroscopical products (pathologies) that can affect historical and modern architectural works. The impact of the decay processes is related to the susceptibility of the materials, environmental conditions and the kind of pollutants that degrade building materials. Here are reviewed the main decay processes resulting from the actions of gases, particulate matter and solutions (from wet deposition to capillary rising and including circulating waters such as run-off), showing that besides atmospheric pollution, also pollutants rising from the ground can cause important deterioration on building materials. Following, the use of tracers is considered for the study of pollutant sources and migration, including neoformation minerals (that might also constitute markers of environmental conditions) and chemical tracers, giving special attention to isotopic tracers, namely to proposals regarding the use of some stable and radioactive isotopes for the study of pollutants that have strong potential but have not been tested yet are also presented. At the end of this chapter, some final considerations are made on the problem of durability assessment of materials in the built environment and also on the use of tracers to assess the origin of damaging compounds in the built environment.

Application of benzo[a]phenoxazinium chlorides in antimicrobial photodynamic therapy of Candida albicans biofilms

The use of Antimicrobial Photodynamic Therapy (APDT) as a new approach to treat localized Candida infections is an emerging and promising field nowadays. The aim of this study was to verify the efficacy of photodynamic therapy using two new benzo[a]phenoxazinium photosensitizers against Candida albicans biofilms: N-(5-(3-hydroxypropylamino)-10-methyl-9H-benzo[a]phenoxazin-9-ylidene)ethanaminium chloride (FSc) and N-(5-(11-hydroxyundecylamino)-10-methyl-9H-benzo[a]phenoxazin-9-ylidene)ethanaminium chloride (FSd). The photodynamic activity of dyes against C. albicans biofilms was evaluated by incubating biofilms with dyes in the range of 100-300 μM for 3 or 18 h followed by illumination at 12 or 36 J cm(-2), using a xenon arc lamp (600 ± 2 nm). A total photoinactivation of C. albicans biofilm cells was achieved using 300 μM of FSc with 18 h of incubation, followed by illumination at 36 J cm(-2). Contrarily, FSd had insignificant effect on biofilms inactivation by APDT. The higher uptake of FSc than FSd dye by biofilms during the dark incubation may explain the greater photodynamic effectiveness achieved with FSc. The results obtained stresses out the FSc-mediated APDT potential use to treat C. albicans infections.

Pore structure and durability of Portuguese limestones: a case study

Abstract Exposed stone surfaces containing complex systems of pores, fractures and grain boundaries provide the surfaces where chemical, physical and biological deterioration processes take place. The pore space represents the preferred area for physical, chemical and biological weathering processes. It plays a significant role in the behaviour of porous materials. A full understanding of pore-channel network morphology, size and connectivity is important in stone decay assessment and conservation works. A contribution to the understanding of the role played by the pore system in controlling fluid-related properties and resistance to salt crystallization of limestones is presented. Optical microscopy, scanning electron microscopy (SEM) and mercury injection porosimetry (MIP) were used to characterize the pore structure of two Portuguese dimension stones (‘Semi-rijo’ and ‘Moca-Creme’) widely used for pavements and the cladding of buildings. Fluid migration physical tests (open and free porosity, capillary imbibition, and Hirschwald coefficient) were also performed, according to European (EN 1925:1999; EN 1936:1999) and French (N FB 10-504:1973) Standards. The resistance to salt crystallization was determined using European Standard EN 12370:1999. An integrated analysis facilitated comparison between durability results with stone pore network characteristics, fluid transport properties and petrographical features, suggesting the influence of available porosity and bedding.

White Crusts on Recent Buildings

Materials applied in buildings, sculptures and other civil engineering, architectural or artistic works can be affected by coatings of neoformation products, namely salts. Carbonate rich (typically calcite) coatings are common in recent constructions. They generally have a visual impact (frequently present a vertical streaking pattern and it could be argued that the aesthetic effect of white crusts on dark-coloured stones is similar to that of black crusts on light-coloured stones). The thickness and extension that can be achieved in some cases can be considered an important defacement process that develops in relatively small periods of time. There are evidences that in some situations the process might be recurrent with time. Its chromatic evolution with time could also contribute to increasing heterogeneity with aesthetic consequences. An interesting question regarding these crusts is the possible contribution of certain building materials to its formation, materials that will be, in this way, potential pollution sources that might affect other building materials.