Differential Resistance to Oxidants and Production of Hydrolytic Enzymes in Candida albicans

Candida biome of severe early childhood caries (S-ECC) and its cariogenic virulence traits

The protected niche of deep-caries lesions is a distinctive ecosystem. We assessed the Candida biome and its cariogenic traits from dentin samples of 50 children with severe-early childhood caries (S-ECC). Asymptomatic, primary molars belonging to International Caries Detection and Assessment-ICDAS caries-code 5 and 6 were analyzed, and C. albicans (10-isolates), C. tropicalis (10), C. krusei (10), and C. glabrata (5) isolated from the lesions were then evaluated for their biofilm formation, acidogenicity, and the production of secreted hydrolases: hemolysins, phospholipase, proteinase and DNase. Candida were isolated from 14/43 ICDAS-5 lesions (32.5%) and 44/57 ICDAS-6 lesions (77.2%). Compared to, ICDAS-5, a significantly higher frequency of multi-species infestation was observed in ICDAS-6 lesions (p=0.001). All four candidal species (above) showed prolific biofilm growth, and an equal potency for tooth demineralization. A significant interspecies difference in the mean phospholipase, as well as proteinase activity was noted (p < 0.05), with C. albicans being the predominant hydrolase producer. Further, a positive correlation between phospholipase and proteinase activity of Candida-isolates was noted (r = 0.818, p < 0.001). Our data suggest that candidal mycobiota with their potent cariogenic traits may significantly contribute to the development and progression of S-ECC.

ERG11 couples oxidative stress adaptation, hyphal elongation and virulence in Candida albicans

Candida albicans is a major fungal opportunistic pathogen for humans. In the treatment of C. albicans, azole drugs target the sterol 14α-demethylase (CYP51) encoded by ERG11 gene. Most studies have focused on the fact that the ERG11 mutant results in drug resistance, but its mechanism of action as a drug target has not been described yet. Our results showed that deletion of ERG11 reduced filamentous and invasive growth, and impaired hyphal elongation in sensing serum. Lack of ERG11 increased susceptibility to H2O2 and was defective in clearing reactive oxygen species. ERG11 may affect oxidative stress adaptation by specifically downregulating CAT1 expression. In addition, C. albicans cells lacking ERG11 were more efficiently killed by macrophages and became avirulent in vivo. This study is the first to indicate that ERG11 plays an essential role in hyphal elongation, oxidative stress adaptation and virulence in C. albicans. We speculated that azole drugs not only inhibit the growth of C. albicans, but also assist the host immune system in clearing the fungal organism. The new understanding of mechanisms of action of antifungal drugs should facilitate the development of treatment strategies for resistant fungal infections.

Genetic variability of Candida albicans Sap8 propeptide in isolates from different types of infection

The secreted aspartic proteases (Saps) are among the most studied virulence determinants in Candida albicans. These proteins are translated as pre-pro-enzymes consisting of a signal sequence followed by a propeptide and the mature enzyme. The propeptides of secreted proteinases are important for the correct processing, folding/secretion of the mature enzyme. In this study, the DNA sequences of C. albicans Saps were screened and a microsatellite was identified in SAP8 propeptide region. The genetic variability of the repetitive region of Sap8 propeptide was determined in 108 C. albicans independent strains isolated from different types of infection: oral infection (OI), oral commensal (OC), vulvovaginal candidiasis (VVC), and bloodstream infections (BSI). Nine different propeptides for Sap8 processing were identified whose frequencies varied with the type of infection. OC strains presented the highest gene diversity while OI isolated the lowest. The contribution of the Saps to mucosal and systemic infections has been demonstrated and recently Sap8 has been implicated in the cleavage of a signalling glycoprotein that leads to Cek1-MAPK pathway activation. This work is the first to identify a variable microsatellite in the propeptide of a secreted aspartic protease and brings new insights into the variability of Sap8.

The immunomodulatory effect of propolis on receptors expression, cytokine production and fungicidal activity of human monocytes

OBJECTIVES

Propolis is a beehive product and its immunomodulatory action has been documented; however, little is known concerning its mechanisms of action on human cells. Propolis influence on the initial events of the immune response was assessed, evaluating cell markers, cytokine production and the fungicidal activity of human monocytes.

METHODS

Toll-like receptor (TLR)-2, TLR-4, human leukocyte antigen-DR and cluster of differentiation (CD)80 expression by human monocytes was assessed using a FACSCalibur flow cytometer, cytokine production (tumour necrosis factor (TNF)-α and interleukin (IL)-10) was determined by ELISA and the candidacidal activity was investigated after monocytes incubation with propolis and challenged with Candida albicans. The role of TLR-2 and TLR-4 on propolis action was assessed as well.

KEY FINDINGS

Propolis upregulated TLR-4 and CD80 expression and affected TNF-α and IL-10 production, depending on concentration. Propolis also increased the fungicidal activity of monocytes. Cytokine production was decreased by blocking TLR-4, whereas the fungicidal activity was affected by blocking TLR-2.

CONCLUSIONS

Propolis exerted an immunomodulatory action on cell receptors, cytokine production and fungicidal activity of human monocytes without affecting cell viability and depending on concentration. TLR-2 and TLR-4 may be involved in its mechanism of action.