Origin, prevalence and diversity of foodborne and environmental strains of Bacillus cytotoxicus
(2021)
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- Abstract
- Bacillus cereus s.l. is soil dweller that gathers rode-shape Gram-positive, and spore forming bacteria. The group contains beneficial, non-pathogenic as well pathogenic species. From their natural environment, B. cereus contaminates food products and can cause two types of foodborne diseases: emetic and diarrhoeal syndromes. In 1998, a fatal diarrhoeal outbreak occurred in a nursing house in France. Bacillus cytotoxicus, a thermotolerant B. cereus, was isolated and shown to harbour cytK-1, a gene encoding the most cytotoxic variant of Cytotoxin K, one of the three prominent enterotoxins presumably responsible of the diarrhoeal syndrome. This thesis aimed at exploring the ecological niche of B. cytotoxicus, assessing its diversity and clarifying the role of CytK-1 toxin in B. cytotoxicus cytotoxicity. Our results support that B. cytotoxicus is rare in nature. Overall, 39 out of 339 (11,5%) food and environment samples were positive to B. cytotoxicus, with a high prevalence in potato flakes and potato derived products. From Malian foods though, B. cytotoxicus was also found in Millet flour for children and fish powder for the first time ever. A study case in a potato processing food-industry revealed that B. cytotoxicus and other thermotolerant B. cereus were positively selected by the industrial process. Band-based profiling (RAPD and plasmid profiling) of 57 strains showed six RAPD patterns and eleven plasmids profiles. SNPs computing revealed that strains with RAPD pattern A fitted in genomic clade C while those with pattern D clustered in clade D. Sole members of RAPD patterns E and F did not fit in any genomic clade. Inositol degradation and acetoin anabolism operons, and lactose uptake and utilisation coding genes were first ever reported in B. cytotoxicus. Prophages sequences and plasmid content played a role in genomic diversity the species. A mutant lacking in cytK-1 gene showed significantly decreased cytotoxicity. This indicates that CytK-1 is the main toxin responsible of B. cytotoxicus toxicity
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Citations
Kone, K. M. (2021). Origin, prevalence and diversity of foodborne and environmental strains of Bacillus cytotoxicus. https://hdl.handle.net/2078.5/107227