Project description:Pathogenic species belonging to Bacillus cereus sensu lato group possess a high evolutionary advantage in the environment and in food matrices thanks to their capacity to survive as silent spores to harsh environmental insults and grow at relatively low temperatures. Ready to re-heat products are at severe risk for contamination by members of Bacillus cereus s.l. group if not stored at proper conditions. In this work, the goal was to assess, by means of a genome-wide transcriptional assay, the isolated strain Bacillus cereus UC10070 gene expression behind the process of spore germination and consequent outgrowth in an artificially contaminated vegetable-based food model. A vegetable food model subjected to a heat treatment was determined to present favourable conditions for spores germination. Microscopic analyses together with OD measurements were applied to select the key steps of B. cereus cell cycle to be used for the microarray analysis. Using this approach we found a total of 1,646 probe sets differentially expressed and modulated during the entire B. cereus life cycle in the vegetable foodstuff.
Project description:The aim of the study was to carry out a CGH study utilizing a set of 39 diverse Bacillus isolates. Thirty four B. cereus and five B. anthracis strains and isolates were chosen so as to represent different lineages based on previous characterizations, including MLEE and MLST (Helgason, Okstad et al. 2000; Helgason, Tourasse et al. 2004). They represent the spectrum of B. cereus phenotypic diversity by including soil, dairy and periodontal isolates in addition to virulent B. anthracis strains.
Project description:Pathogenic species belonging to Bacillus cereus sensu lato group possess a high evolutionary advantage in the environment and in food matrices thanks to their capacity to survive as silent spores to harsh environmental insults and grow at relatively low temperatures. Ready to re-heat products are at severe risk for contamination by members of Bacillus cereus s.l. group if not stored at proper conditions. In this work, the goal was to assess, by means of a genome-wide transcriptional assay, the isolated strain Bacillus cereus UC10070 gene expression behind the process of spore germination and consequent outgrowth in an artificially contaminated vegetable-based food model. A vegetable food model subjected to a heat treatment was determined to present favourable conditions for spores germination. Microscopic analyses together with OD measurements were applied to select the key steps of B. cereus cell cycle to be used for the microarray analysis. Using this approach we found a total of 1,646 probe sets differentially expressed and modulated during the entire B. cereus life cycle in the vegetable foodstuff. RNA was isolated from the dormant spores (DS), germinating spores at 40 minutes (GSP), early-log phase at 2h (C2h) and late log phase cells at 12 hours (C12h) after thermal treatment of B. cereus UC10070 previously isolated froma biofilm on a spoiled vegetable-based puree. There were 3 biological replicates (independent cultures) for each condition. Complete genome sequence of B. thuringiensis sv konkukian str. 97-27 (NCBI Reference Sequence: NC_005957.1) was chosen for its high homology with B. cereus s.l. UC10070, to design probes corresponding to 5,197 genes spotted in duplicates onto ElectraSenseH 12K microarrays chip.
Project description:A comparative transcriptome approach was used to assess genes involved in metabolism and pathogenesis that are specifically activated during anaerobic growth of the spore-forming food-borne human pathogen Bacillus cereus ATCC 14579. Growth under anaerobic conditions in Brain Heart Infusion broth revealed a reduced growth rate and a lower yield as compared to that under aerobic conditions. Comparative transcriptome analysis of cells harvested at early- and mid-exponential growth phase, transition phase and stationary phase, subsequently showed hundreds of genes to be induced under anaerobic condition. These included novel genes identified for anaerobic growth of B. cereus, encoding metabolic pathways, such as the arginine deiminase pathway (ArcABDC), a formate dehydrogenase (FdhF) and a pyruvate fomate lyase (Pfl), and alternative respiratory proteins, such as arsenate reductases. Furthermore, the nitrosative stress response was induced in the anaerobic transition phase of growth, conceivably due to the production of nitric oxide as a by-product of nitrite and nitrate respiration. Notably, both hemolytic enzyme and enterotoxin encoding genes were activated in different oxygen limiting conditions, i.e. hemolytic enzyme encoding genes were induced during anaerobic growth, whereas enterotoxin encoding genes were induced in the transition and stationary phase of aerobic cultures reaching a high cell density. These data point to metabolic rearrangements, stress adaptation and activation of the virulent status of B. cereus under anaerobic conditions, such as encountered in the human GI-tract. Keywords: time course, anaerobic growth