Proteome screening of Bacillus cereus derived extracellular vesicles

Extracellular vesicles (EVs) from Gram-positive bacteria have gained considerable importance as a novel transport system of virulence factors in host-pathogen interactions. Bacillus cereus is a Gram-positive human pathogen, causing gastrointestinal toxemia as well as local and systemic infections. The pathogenicity of the B. cereus has been linked to a collection of virulence factors and exotoxins. Nevertheless, the exact mechanism of virulence factor secretion and delivery to target cells is poorly understood. Here, we investigate the production and characterization of enterotoxin-associated EVs from the enteropathogenic B. cereus strain NVH0075-95 by using a proteomics approach and studied their interaction with human host cells in vitro. Proteomic analysis of B. cereus EVs revealed virulence-associated factors, such as sphingomyelinase, phospholipase C, and the three-component enterotoxin Nhe. The detection of Nhe subunits was confirmed by immunoblotting, showing that the low abundant subunit NheC was exclusively detected in EVs as compared to vesicle-free supernatant. Fusion of B. cereus EVs with the plasma membrane of intestinal epithelial Caco2 cells represent entry routes for delivery of Nhe components to host cells, which was assessed by confocal microscopy. B. cereus EVs also elicit an inflammatory response in human monocytes and contribute to erythrocyte lysis via a cooperative interaction of enterotoxin Nhe and sphingomyelinase. Our results provide insights into the interaction of EVs from B. cereus with human host cells and add a new layer of complexity to our understanding of multicomponent enterotoxin assembly, offering new opportunities to decipher molecular processes involved in disease development.