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Subject: search.filters.subject.Bacillus cereus

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    Characterization, antibacterial activity, and stability of supercritical fluid extracted lemongrass nanoemulsion on Bacillus cereus
    (Elsevier Ltd, 2025-06) Mohd Daud IS; Mahmud Ab Rashid NK; Palmer J; Flint S
    Natural food preservation is a sustainable approach to extend shelf life, combat foodborne pathogens and enhance food safety. Bacillus cereus, a resilient contaminant, poses challenges due to its spore-forming ability and association with foodborne illnesses. This study investigates the characterization, antimicrobial activity, and stability of lemongrass (Cymbopogon citratus) nanoemulsions, extracted using supercritical fluid extraction (SFE), and their efficacy against B. cereus isolates (ATCC 14579, P4, and M2). Lemongrass oil was extracted at 85, 100, 200, and 300 bar, with the highest yield (0.815 %) obtained at 300 bar. Nanoemulsions were formulated with lemongrass extract and commercial citral, characterized for droplet size, polydispersity index (PDI), conductivity, and zeta potential, and assessed for antimicrobial activity. Lemongrass nanoemulsions initially had droplet sizes of 86.32 ± 0.66 nm, but increased over six months due to coalescence, with PDI values rising from 0.50 ± 0.00 to 0.81 ± 0.27, indicating reduced stability. Although zeta potential declined from −44.01 ± 1.69 mV to −33.63 ± 1.45 mV, it remained within the stable range (>±30 mV), maintaining sufficient electrostatic repulsion to prevent rapid aggregation. At 2.0 % concentration, nanoemulsions effectively suppressed B. cereus isolates (<1.00 CFU/mL), though efficacy declined after four months with increasing droplet size. Lemongrass nanoemulsions exhibited comparable antibacterial activity and stability trends to citral, suggesting that whole lemongrass extract retains its bioactivity as effectively as its major compound. Improved stabilization strategies, such as polymer encapsulation, could enhance shelf life, expanding applications in food preservation.
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    Phenotypic properties and genotyping analysis of Bacillus cereus group isolates from dairy and potato products
    (Elsevier Ltd, 2021-04) Huang Y; Flint SH; Yu S; Ding Y; Palmer JS
    Bacillus cereus group (B. cereus sensu lato) are ubiquitously distributed in diverse environments. In this study, eight isolates including B. cereus, B. paranthracis and B. toyonensis species, from dairy and potato products, were assessed for biofilm formation, sporulation and genetic information including biofilm-related genes and toxin genes. The isolates varied in their ability to form biofilm (either at the stainless steel-liquid-air interface or floating pellicles). The amounts of biofilms of B. cereus s.l., were increased when incubated in agitation condition varied between isolates. Sporulation within the planktonic and biofilm modes of growth was compared, suggesting that biofilm is a favourable environment for B. cereus s.l. to form spores. Whole genome sequencing (WGS) was used to compare these B. cereus s.l. isolates. New sequence types (STs) of B. cereus were found in this study. Isolates that shared similar genomes had different biofilm-forming and sporulation abilities. Most of isolates tested, possessed biofilm-related genes. Different combinations of toxin-producing genes were identified in different isolates, with all isolates containing nhe while only some contained hbl and cytK. None of the food isolates contained the emetic ces gene. This study highlights the diversity of B. cereus s.l. in biofilm formation, sporulation and their genetic variables.
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    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
    (Massey University, 2021) Huang, Yiying
    Bacillus 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.
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    Survey of naturally fermented raw milk in Bhutan for the prevalence of Bacillus cereus, Escherichia coli and Staphylococcus aureus : a thesis presented in partial fulfilment of the requirements for the degree of Master in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2019) Zangmo, Tashi
    In Bhutan, naturally fermented raw milk (NFRM) is an ethnic dairy product consumed as a nutritional and refreshing beverage. It is produced by spontaneously fermenting raw milk at ambient temperatures. Across the globe, raw milk and raw milk products are considered as high-risk foods that may contain human pathogens. However, no survey has been conducted to study the presence of pathogens in NFRM in Bhutan. Therefore, in the present survey, 114 NFRM samples from 19 milk outlets and stalls in Thimphu, Phuntsholing and along the Thimphu-Phuntsholing NH (NH) in Bhutan were screened for the presence of Escherichia coli, Bacillus cereus and Staphylococcus aureus using culture-independent (high throughput sequencing (HTS)) and culture-dependent methods (most probable number (MPN) and selective plating). The culture isolates were confirmed by the PCR using species-specific primers. HTS identified the Escherichia and Staphylococcus genera. The culturing methods found more than 90 % and 100 % of NFRM samples contaminated with E. coli and S. aureus respectively. 45 % of NFRM samples contained more than 3.04 log10 cfu/ml E. coli based on MPN estimates. 61 % of NFRM samples contained more than 4 log10 cfu/ml S. aureus and is an immediate food safety concern. B. cereus was suspected since HTS detected Bacillus anthracis which is closely related to B. cereus. Shigella and Vibrio genera, and Streptococcus agalactiae and Streptococcus parauberis were also identified by HTS. Ideally, fermented milk products including NFRM should be prepared from pasteurised milk and fermented using commercial starter cultures since pasteurisation is the most effective method to inactivate the vegetative pathogens and ensure the safety of the product. Hygienic practices and control measures during NFRM production should also be adopted to minimise bacterial contamination in NFRM in Bhutan.
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    Microbiological and chemical risk assessments of the addition of selected cereal grains as non-dairy ingredients to dairy products : a thesis presented in partial fulfilment of the requirements for the degree of Master in Food Technology at Massey University, Manawatū, New Zealand
    (Massey University, 2019) Fatima, Fitry
    Food poisoning cases involving non-dairy ingredients such as cereal grains have been reported. The addition of cereal grains to dairy products in the dairy industry has increased in recent years. This has the potential to contaminate final products with pathogenic, spoilage and toxic chemical contaminants. In this study, the microbial and chemical risks involved in the addition of cereal grains to dairy products were assessed using semi- quantitative risk assessment method. The results showed that the most critical microbiological hazard in the selected cereal grains is Bacillus cereus due to its ability to form spores and persist in cereal grains. The addition of cereal grains to dairy products with high water activity/moisture content such as liquid breakfast products were found to pose the highest risk. Cyanogenic glycosides (hydrocyanic acid) were found to be the most critical chemical hazard among natural plant toxins in selected cereal grains due to their adverse health effects and abundance in most cereal grains. The addition of cereal grains to dairy products with high solid content was found to pose a very low risk. The results have identified some knowledge gaps in conducting risk assessments and have also provided background information about the microbial and chemical risks involved in the addition of cereal grains to dairy products. The results highlight the importance of effective implementation of Hazard Analysis and Critical Control Point (HACCP), Good Manufacturing Practices (GMP) and Good Hygienic Practices (GHP) in the dairy industry.