In-vitro and in-vivo regulation of Candida albicans morphogenesis and pathogenesis by probiotic bacterium – Pediococcus acidilactici.  
Zare, Zomorodian, Rezaei,  Mehrabani 
Basic Sciences in Infectious Diseases Research Center, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran
Objectives: Candida species is known as opportunistic yeast that could cause candidiasis in susceptible indivituals. Oral candidiasis is one of most frequent form of this infection that caused by Candida species in particular, Candida albicans which normally reside on human mucosal surfaces. The transition of Candida albicans, from budding yeast to filamentous hyphae allows for covalent attachment to oral epithelial cells, followed by biofilm formation, invasion and tissue damage. It has been suggested that biofilm formation by Candida albicans play important role in its pathogenesis. Hence, the effect of Pediococcus acidilactici on the growth, biofilm formation and expression of genes related to morphogenesis and pathogenesis of Candid albicans were investigated in vitro as well as in animal model. 
Methods: Inhibitory activity of Pediococcus acidilactici on Candida species was evaluated by broth microdilution method based on CLSI protocol. Moreover, inhibition of Candida albicans biofilm formation by Pediococcus acidilactici was measured using XTT reduction assay. Also, expression of adhesion-related gene (ALS1), hyphal cell wall protein gene critical to biofilm formation (HWP1), secreted aspartyl proteinase(SAP6), morphogenesis pathway regulatory gene (EFG1) were analyzed by RT-PCR in the treated yeast cells with different concentrations of Pediococcus acidilactici. The experimental activity of the probiotic bacterium in the prevention or treatment of oral candidiasis was also assessed in an animal model by both culture and histopathological methods. 
Results: Pediococcus acidilactici inhibited the growth of different species of candida at concentration ranging from 8 µg/mL to 256 µg/mL. Furthermore, this probiotic bacterium inhibited the formation of Candida albicans biofilm in a dose dependent manner. RT-PCR analysis of Candida albicans yeast treated with different concentration of probiotic bacterium showed reduction of ALS1, SAP6 EFG1 and HWP1 genes.  The Pediococcus acidilactici significantly decreased the CFUs in mice receiving this probiotic treatment compared to those of control group. Similarly, histopathological analyses showed that Candida colonization declined in the mice following administration of probiotic in a therapeutic trial.
Conclusion:  Obtained data provided new insight into the effect of probiotic bacteria on growth, transition, biofilm formation and pathogenicity of Candida and uncover novel probiotic functions. Moreover, the results suggest that probiotics may have the potential to reduce or even inhibit yeast colonization on mucosal surfaces. 
Key word: Candida, Pediococcus acidilactici, ALS1, SAP6, EFG1 and HWP1 and quantitative real-time PCR