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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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Record number 356790
Title Germination of Bacillus cereus spores : the role of germination receptors
Author(s) Hornstra, L.M.
Source Wageningen University. Promotor(en): Tjakko Abee; Willem de Vos. - [S.l.] : S.n. - ISBN 9789085046721 - 154
Department(s) Food Microbiology
Microbiology
VLAG
Publication type Dissertation, internally prepared
Publication year 2007
Keyword(s) bacillus cereus - bacteriële sporen - sporenkieming - voedselveiligheid - bacillus cereus - bacterial spores - spore germination - food safety
Categories Food Microbiology
Abstract The Bacillus cereus sensu lato group forms a highly homogeneous subdivision of the genus Bacillus and comprises several species that are relevant for humans. Notorious is Bacillus anthracis, the cause of the often-lethal disease anthrax, while the insect pathogen Bacillus thuringiensis is of economical importance, being used worldwide as an insecticide. B. cereus is a food pathogen, and can cause two types of foodborne diseases leading to an emetic- or diarrheal syndrome. The capacity of these bacteria to form highly resistant dormant particles, called spores, enables them to survive extreme conditions. Under favorable conditions, spores may germinate, herewith instantaneously loosing their resistance capacities, and grow out to vegetative cells. The research in this thesis describes the germination of spores of B. cereus. Precise timing of germination is crucial for survival. Therefore, the spore contains specific sensors, called germination receptors, which monitor the environment continuously for components necessary for growth. By systematically disrupting the complete set of B. cereus ger operons, coding for germination receptors, we revealed new germination-initiating molecules for the receptors. The GerR receptor was found to have a prominent role in germination, and appeared to be involved in initiation of germination by most of the amino acid- and purine ribosides. GerG showed participation in L-glutamine-initiated germination, while GerI played a role in purine riboside-initiated germination and the combined amino acid/purine riboside responses. Exposure of B. cereus spores to Caco-2 cells, that mimic the epithelial layer of the human small intestine, induced a strong germination response. The involvement of the germination receptors in this response was shown and found to be mainly mediated by GerI. It was furthermore shown that the nutrient content during sporulation defined the transcription levels of the ger operons and affected spore germination properties, suggesting that sporulation conditions influence the number of Ger receptors in the spore. The obtained knowledge was used to develop an improved cleaning-in-place method for inactivation of attached B. cereus spores. These spores are a frequent problem in processing equipment used in the food industry and the cause of a continuous source of contamination. The results presented are expected to contribute to a better understanding of Bacillus spore germination, and to facilitate the development of new food preservation strategies that will contribute to a better control of spores in our food products.
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