Potato crop as a source of emetic bacillus cereus and cereulide-induced mammalian cell toxicity

Abstract

Bacillus cereus, aseptically isolated from potato tubers, were screened for cereulide production and for toxicity on human and other mammalian cells. The cereulide-producing isolates grew slowly, the colonies remained small (~1 mm), tested negative for starch hydrolysis, and varied in productivity from 1 to 100 ng of cereulide mg (wet weight)-1 (~0.01 to 1 ng per 105 CFU). By DNA-fingerprint analysis, the isolates matched B. cereus F5881/94, connected to human food-borne illness, but were distinct from cereulide-producing endophytes of spruce tree (Picea abies). Exposure to cell extracts (1 to 10 μg of bacterial biomass ml-1) and to purified cereulide (0.4 to 7 ngml-1) from the potato isolates caused mitochondrial depolarization (loss of ΔΨm) in human peripheral blood mononuclear cells (PBMC) and keratinocytes (HaCaT), porcine spermatozoa and kidney tubular epithelial cells (PK-15), murine fibroblasts (L-929), and pancreatic insulin-producing cells (MIN-6). Cereulide (10 to 20 ng ml-1) exposed pancreatic islets (MIN-6) disintegrated into small pyknotic cells, followed by necrotic death. Necrotic death in other test cells was observed only after a 2-log-higher exposure. Exposure to 30 to 60 ng of cereulide ml-1 induced K+ translocation in intact, live PBMC, keratinocytes, and sperm cells within seconds of exposure, depleting 2 to 10% of the cellular K+ stores within 10 min. The ability of cereulide to transfer K+ ions across biological membranes may benefit the producer bacterium in K+-deficient environments such as extracellular spaces inside plant tissue but is a pathogenic trait when in contact with mammalian cells. © 2013, American Society for Microbiology. All Rights Reserved.