Food epidemiology of emetic Strains of Bacillus cereus and Bacillus weihenstephanensis
(2012) American Society of Micorbiology — Location: San Francisco (14.June.2012)
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120457_ASM_SanFranscico.pdf
Closed Access - Adobe PDF
- 1.38 MB
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- et. al.
- Abstract
- Cereulide, the emetic toxin of Bacillus cereus, is an important foodborne toxin implicated in lethal poisoning. It is structurally related to valinomycin, an antibiotic produced by Streptomyces spp. Both compounds are cyclododecadepsipeptides produced via nonribosomal peptide synthesis. The aim of this study was to gather more insights into the ecology and epidemiology of the emetic strains of B. cereus, including their prevalence and diversity in food and environmental niches. A collection of more than 1,500 strains of B. cereus sensu lato have been tested for the presence of the genetic determinants of the cereulide using primer pairs targeting the ces (cereulide synthetase) cluster. The potential candidates were confirmed for the production of cereulide by the boar sperm assay. These strains were then characterized phenotypically and genotypically using biochemical tests (API), and molecular techniques (PFGE and MLST). Bacterial cereulide extracts were used to test their activities on various species of bacteria and fungi. The prevalence of cereulide was also tested in rice dishes collected from various restaurants using LC-MS² method for the direct quantification of the toxin in food. Emetic strains of B. cereus and Bacillus weihenstephanensis are rare in both environmental niches and food matrices were they represent ca. 1-2 % of the tested strains. The detailed study on their diversity revealed that existence of two distinct clusters: a mesophilic group of B. cereus strains and a cluster of psychrotrophic strains displaying features of B. weihenstephanensis. Interestingly, the same emetic clones have been isolated in distinct (time and location) food intoxication cases, but different clones have also been associated with a single incident. These important observations are currently under scrutiny to identify the common source(s) of the primary B. cereus contamination. Finally, preliminary data of the prevalence of cereulide in ready to eat rice dishes was found to be ca. 7 % when samples were analyzed at the day of sampling but reached about 13 % when exposed to temperature abuse conditions. However, the cereulide concentrations present in the cooked rice dishes (ng/g of food) do not represent an acute risk for the public health but deserve further attention for potential chronic toxicity. Financial supports by the Belgian Federal Science Policy, FNRS, FRIA and UCL are gratefully acknowledged.
Citations
Castiaux, V., Delbrassinne, L., Dierick, K., Mahillon, J., & et al. (2012). Food epidemiology of emetic Strains of Bacillus cereus and Bacillus weihenstephanensis. American Society of Micorbiology, San Francisco. https://hdl.handle.net/2078.5/46962