Candida albicans Adaptation on Simulated Human Body Fluids under Different pH

Abstract

Candida albicans remains the most problematic of all Candida species, causing severe infections. Adaptation to different human body niches, such oral and urinary tracts, has been shown to be essential for survival and critical for virulence of C. albicans. Thus, the present work aimed to study the behaviour of C. albicans on simulated human body fluids (artificial saliva and urine) at different values of pH (pH 5.8 and 7) by determining its ability to develop two of the most important virulence factors: biofilms and filamentous forms. Under this study, it was demonstrated that C. albicans was able to grow as free cells and to develop biofilm communities composed of multiple cell types (yeast and elongated hyphal cells) on both simulated human body fluids and under different pH. It was interesting to note that the pH had little impact on C. albicans planktonic and biofilm growth, despite influencing the development of filamentous shapes in artificial saliva and urine. So, it was possible to infer that C. albicans presents a high plasticity and adaptability to different human body fluids, namely saliva and urine. These can be the justification for the high number of oral and urinary candidiasis in the whole world.

Keywords: candidiasis; environmental cues; pathogenicity; virulence factor.

Figure 1

Candida albicans planktonic growth on simulated human body fluids. (a) Growth curves and specific growth rates over 30 h (b) Number of cultivate cells (log₁₀ colony forming units (CFUs) and (c) Metabolic activity determination by XTT reduction (Abs 490 nm/log₁₀ CFUs) obtained for planktonic growth of C. albicans SC5314 in Roswell Park Memorial Institute (RPMI) pH 7, artificial saliva (AS) (pH 5.8 and pH 7) and artificial urine (AU) (pH 5.8 and pH 7), at 24 h. Error bars represent standard deviation. * Significant difference between RPMI and simulated fluid (p-value < 0.05).

Figure 2

Candida albicans biofilm formation on simulated human body fluids. (a) Cultivate cells enumeration (log₁₀ CFUs cm⁻²); (b) Metabolic activity determination by XTT reduction (Abs 490 nm/ log¹⁰ CFUs) and (c) Total biomass quantification (Absorbance CV cm⁻²) of C. albicans SC5314 of formation in RPMI (pH 7), AS (pH 5.8 and 7) and AU (pH 5.8 and 7) developed over 24 h. Error bars represent standard deviation. * Significant differences between RPMI and simulated fluid (p-value < 0.05); ** Significant differences between pH at the same body fluid (p-value < 0.05); *** Significant differences between AS and AU for the same pH (p-value < 0.05).

Figure 3

Candida albicans planktonic and biofilms cells filamentation on simulated human body fluids. Filamentous forms percentage of C. albicans SC5314 cells grown in (a) planktonic and (b) biofilm lifestyle in RPMI (pH 7), AS (pH 5.8 and 7) and AU (pH 5.8 and 7) over 24 h. * Significant differences between RPMI and simulated fluids at the same time point (p-value < 0.05); ** Significant differences between pH at the same body fluid (p-value < 0.05); ⁺ Significant differences for the same simulated fluid at different time points (p-value < 0.05).

Figure 4

Candida albicans planktonic and biofilms cells filamentation on simulated human body fluids. Fluorescence microscopy images of C. albicans SC5314 grown in planktonic and biofilm lifestyle in RPMI (pH 7), AS (pH 5.8 and 7) and AU (pH 5.8 and 7) at 24 h. Original magnification was 10× for RPMI and 40× for simulated fluid. Arrows highlight filamentous forms.