Unveiling the Morphostructural Plasticity of Zoonotic Sporotrichosis Fungal Strains: Possible Implications for Sporothrix brasiliensis Virulence and Pathogenicity

Abstract

Sporotrichosis is a fungal infection caused by Sporothrix species, with Sporothrix brasiliensis as a prevalent pathogen in Latin America. Despite its clinical importance, the virulence factors of S. brasiliensis and their impact on the pathogenesis of sporotrichosis are still poorly understood. This study evaluated the morphostructural plasticity of S. brasiliensis, a fungus that causes sporotrichosis. Three cell surface characteristics, namely cell surface hydrophobicity, Zeta potential, and conductance, were assessed. Biofilm formation was also analyzed, with measurements taken for biomass, extracellular matrix, and metabolic activity. In addition, other potential and poorly studied characteristics correlated with virulence such as lipid bodies, chitin, and cell size were evaluated. The results revealed that the major phenotsypic features associated with fungal virulence in the studied S. brasiliensis strains were chitin, lipid bodies, and conductance. The dendrogram clustered the strains based on their overall similarity in the production of these factors. Correlation analyses showed that hydrophobicity was strongly linked to the production of biomass and extracellular matrix, while there was a weaker association between Zeta potential and size, and lipid bodies and chitin. This study provides valuable insights into the virulence factors of S. brasiliensis and their potential role in the pathogenesis of sporotrichosis.

Keywords: biofilm; biophysics; chitin; lipid bodies; one health; virulence factors.

Figure 1

Cell surface properties of cat- and human-derived cases of S. brasiliensis. The CSH was evaluated by the two-phase partition (water-octane) method. Zeta potential and conductance was evaluated using a Zeta potential analyzer. CSH (A), Zeta potential (B), and conductance (C). Each dot represents the mean value of three independent experiments performed in technical triplicates. Dot colors and numbers after dots represent the different familial outbreaks. Black lines represent the median value of each group of strains.

Figure 2

Biofilm formation by S. brasiliensis on a polystyrene surface. Yeasts (10⁶ cells in 100 µL) were placed to interact with polystyrene for 7 days at 35 °C. Fungal biomass via incorporation of crystal violet at 590 nm (A), extracellular matrix via staining the non-fixed biofilms with safranin at 530 nm (B), and viability (C) via the reduction of assay. The results are expressed as median (A,B) and SD (C).

Figure 3

Relative detection of lipid bodies (A) and chitin (B) produced by S. brasiliensis. For lipid bodies detection, fungal cells were labeled with the fluorochromes, Nile red (A) and Uvitex 2B, and evaluated via flow cytometry. The results were expressed as median of fluorescence intensity (MFI) of S. brasiliensis fluorescent cells of three independent experiments.

Figure 4

Scanning electron microscopy (SEM) image of S. brasiliensis yeasts; 6H (A) and 6C (B). Scale bar: 20 µm.

Figure 5

Object area analysis in (pixel/µm²) of S. brasiliensis yeasts. Results are expressed as the median of the measurements.

Figure 6

Global expression of putative virulence-associated factors of S. brasiliensis strains from 12 familial outbreaks of sporotrichosis. The gray scale in the heatmap ranges from low (white) to high virulence (black). Different strains are represented in the lines of the heatmap, and the different virulence factors herein studied in the columns of the heat map. Strains were grouped in a dendrogram reflecting the similarity between the virulence-related phenotypes of each strain. Colors of the strain identification numbers represent the different familial outbreaks.

Figure 7

Correlation analyses of the virulence-associated factors produced by the S. brasiliensis strains from 12 familial outbreaks of sporotrichosis. The heat map represents the Spearman’s correlation coefficients of the associations. Red color represents negative monotonic correlations, whereas the blue color represents positive monotonic correlations. Probability values of statistically significant correlations (p-value < 0.05) are displayed within the respective squares of the heat map.