The rice culture filtrate of Bacillus cereus isolated from emetic-type food poisoning causes mitochondrial swelling in a HEp-2 cell

Abstract

Rice culture filtrates of Bacillus cereus SA-50, an emetic-type strain, produced a toxin which caused cytoplasmic vacuole formation in HEp-2 and HeLa cells. Electron microscopic observation revealed that the apparent vacuoles in HEp-2 seen under a light microscope were actually swollen mitochondria. The oxygen consumption of HEp-2 cells was accelerated by the addition of the rice culture filtrate as was measured with a polarographic oxymeter; a respiratory control ratio was 1.0 for control cells, while 1.4 for ones with the filtrates. The culture filtrates showed a similar effect on the isolated mouse liver mitochondria; respiratory control ratios for the mitochondria with and without the filtrates were 3.6 and 1.0, respectively. The affecting manner of the culture filtrates on the oxygen consumption of mitochondria was similar to that of 2,4-dinitrophenol, suggesting that the culture filtrate contains a toxin acting as an uncoupler of oxidative phosphorylation in mitochondria. It is likely that the culture filtrates containing the emetic toxin of B. cereus causes mitochondrial swelling with a close relationship to the uncoupling of the oxidative phosphorylation of mitochondria.