Characterization of the interaction of undomesticated Bacillus subtilis spores with Caco-2 cell line

Abstract

In spite of increasing tendency toward Bacillus probiotics, specially Bacillus subtilis, proposed for prophylactic and therapeutic use against several gastrointestinal diseases, interaction of their spores with host cells has been poorly understood. In this study, 11 isolates out of 33 B. subtilis isolates prepared from the faeces of patients with colorectal cancer and their healthy spouses were selected according to their ability for sporulation under strict anaerobic conditions. To address what happened to their spores in contact with intestinal-like epithelial cells, adhesion and invasion assays were done on a differentiated Caco-2 cell line. The results showed that most of the clinical isolates of B. subtilis spores, in contrast to the domesticated strains; PY79 and PTCC 1365, could adhere (0.5 to 4.5%) and internalize (0.3 to 2%) to this cell line and respond to this nich by producing atypical colony morphology, probably as an adaptive marker. There were no evident differences between the spores derived from the patients and their healthy spouses in these traits. The SEM images proposed that the interaction of these spores, at least in Caco-2 cells, is probably mediated through their initial attachment to the extra cellular matrix and also due to the local changes in the cell cytoskeleton thereafter, a mechanism reminiscent of zipper-like entry in other bacteria.