The spore formation and toxin production in biofilms of Bacillus cereus : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand

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dc.confidentialEmbargo : Noen_US
dc.contributor.advisorPalmer, Jon
dc.contributor.authorHuang, Yiying
dc.date.accessioned2022-02-10T23:46:19Z
dc.date.accessioned2022-05-11T02:24:09Z
dc.date.available2022-02-10T23:46:19Z
dc.date.available2022-05-11T02:24:09Z
dc.date.issued2021
dc.descriptionListed in 2022 Dean's List of Exceptional Thesesen
dc.description.abstractBacillus cereus (B. cereus) is a foodborne pathogen causing diarrhoea and emesis which are the consequences of enterotoxin and emetic toxin production, respectively. Sporulation and biofilm formation are used as survival strategies by B. cereus protecting cells from harsh environments. However, these survival strategies also make B. cereus more difficult to control in the food industry. The aim of this study is to investigate the spore formation and toxin production in the biofilm of B. cereus. In this study, higher sporulation and higher spore heat resistance were demonstrated in biofilms grown on stainless-steel (SS) compared to planktonic populations. The structure of coat in spores isolated from biofilms, the upregulated germination genes in planktonic cells and upregulated sigma factor B in biofilm cells are possible explanations for these observations. The levels of dipicolinic acid (DPA) did not affect the heat resistance of spores harvested from biofilms in this study. Haemolytic toxin (Hbl) was mainly secreted by cells into surrounding media while emetic toxin (cereulide) was associated with cells. Higher Hbl toxin was observed in the presence of biofilms grown on SS compared to either planktonic culture or biofilm grown on glass wool (GW) using the Bacillus cereus Enterotoxin Reverses Passive Latex Agglutination test (BCET-RPLA). This was supported by the significant (P < 0.05) increase in HblACD expression in biofilm cells on SS, using both real-time quantitative PCR (RT-qPCR) and RNA sequencing. The transcriptomic analysis also revealed that biofilms grown on SS had an upregulated secretion pathway, suggesting biofilms of B. cereus grown on SS are more pathogenic than planktonic cells. Unlike the Hbl toxin, cereulide was associated with biofilm cells/structures and attached to the biofilm-forming substrates including SS and GW used in this study. The expression of cerA and cerB was similar between biofilms and planktonic cells using RT-qPCR. This project highlights the importance of biofilms by B. cereus in food safety through the enhanced heat resistance of spores, the higher Hbl toxin production and attached cereulide toxin.en_US
dc.identifier.urihttp://hdl.handle.net/10179/17096
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectBacillus cereusen
dc.subjectBiofilmsen
dc.subjectAnalysisen
dc.subjectBacterial sporesen
dc.subjectEnterotoxinsen
dc.subjectDean's List of Exceptional Thesesen
dc.subject.anzsrc310701 Bacteriologyen
dc.titleThe spore formation and toxin production in biofilms of Bacillus cereus : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealanden_US
dc.typeThesisen_US
massey.contributor.authorHuang, Yiyingen_US
thesis.degree.disciplineFood Microbiologyen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (PhD)en_US
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