Further Insights into the Toxicity of Bacillus cytotoxicus Based on Toxin Gene Profiling and Vero Cell Cytotoxicity Assays.

Johanna Burtscher,Danai Etter,Janine Schlaepfer,Sophia Johler,Michael Biggel

doi:10.3390/toxins13040234

Johanna Burtscher, Danai Etter + Show 3 more

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https://doi.org/10.3390/toxins13040234

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Abstract

Bacillus cytotoxicus belongs to the Bacillus cereus group that also comprises the foodborne pathogen Bacillus cereus sensu stricto, Bacillus anthracis causing anthrax, as well as the biopesticide Bacillus thuringiensis. The first B. cytotoxicus was isolated in the context of a severe food poisoning outbreak leading to fatal cases of diarrheal disease. Subsequent characterization of the outbreak strain led to the conclusion that this Bacillus strain was highly cytotoxic and eventually resulted in the description of a novel species, whose name reflects the observed toxicity: B. cytotoxicus. However, only a few isolates of this species have been characterized with regard to their cytotoxic potential and the role of B. cytotoxicus as a causative agent of food poisoning remains largely unclear. Hence, the aim of this study was to gain further insights into the toxicity of B. cytotoxicus. To this end, 19 isolates were obtained from mashed potato powders and characterized by toxin gene profiling and Vero cell cytotoxicity assays. All isolates harbored the cytK1 (cytotoxin K1) gene and species-specific variants of the nhe (non-hemolytic enterotoxin) gene. The isolates exhibited low or no toxicity towards Vero cells. Thus, this study indicates that the cytotoxic potential of B. cytotoxicus may be potentially lower than initially assumed.

Highlights

B. cytotoxicus belongs to the B. cereus group
Heat-labile toxins, in contrast, such as non-hemolytic enterotoxins (Nhe), hemolysin BL (Hbl), and cytotoxin K (CytK), lead to diarrheal toxico-infections, as toxin production occurs in the small intestine [2,3]
We detected at least one isolate of B. cereus sensu lato in each tested brand of mashed potato powder and found B. cytotoxicus in out of the (95%) purchased samples

Summary

Introduction

B. cytotoxicus belongs to the B. cereus group. This group of endospore-forming bacteria comprises several closely related species that differ significantly in toxicity and pathogenicity potential including probiotic strains, plant growth promoters and biopesticides as well as highly toxic strains, occasionally causing fatalities [1,2]. B. cytotoxicus is known to cause diarrheal symptoms and has not been linked to emetic illness It represents a relatively homogenous species, which is clearly distinguishable from other members of the B. cereus group [4,5]. Et al [10] observed higher toxicity towards human intestinal CaCo-2 cells and Vero cells for CytK1 than for CytK2, which is produced by other members of the B. cereus group As a consequence, they concluded that the high cytotoxic activity of CytK1 may have caused the high virulence of the B. cytotoxicus outbreak strain from France. Within this study, we aimed to sharpen our understanding of the cytotoxic potential of this species To this end, we isolated B. cytotoxicus strains from mashed potato powders in order to characterize their toxin genes and their cytotoxic potential

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