Why is bacillus cereus more heat resistant

Further evaluation with qPCR Warda et al. This selection included the eight genes previously shown to be specifically upregulated during germination and outgrowth of heat damaged B. A mutant strain in one of those candidate genes cdnL1 BC , a putative transcriptional regulator, was slightly but significantly affected in repair and outgrowth of heat treated B. Attempts to construct mutants in BC and BC were unsuccessful.

Therefore, these mutants were excluded from further analysis. Spores of B. The fractions of mildly and severely damaged spores were comparable to the wild type Supplementary Figure S2. The high fraction of damaged spores allows for the assessment of the roles of candidate genes in recovery of heat treated B. The recovery of those mutant spores improved also in rice broth and on BHI agar plates when compared to relative recovery of the wild type.

This suggests that conditions supporting slower growth favor recovery of spores possibly by providing additional time for damage repair. Values are given in percentage relative to the recovery of wild type in given media.

Error bars represent the lower and upper limits of the MPN values expressed in percentage relative to the recovery of wild type in given media. The capacity of spores to repair damage and grow out is not only affected by the processing conditions, but also by spore history and recovery conditions.

Although, several studies report on impact of food components on spore survival and cell growth Carlin et al. Moreover, the standard plate counting methods are generally not sensitive enough to show changes within the fold range.

In practice, product spoilage may result from a single surviving spore and knowledge on behavior of individual spores can assist in risk evaluation. Here we applied a FCM supported single spore sorting approach in combination with MPN methodology, allowing for evaluation of behavior of individually sorted spores with high resolution for both untreated as well as heat treated spores.

Limited information is available on the effect of the recovery media on outgrowth of single damaged spores. In the present study, we focused on the effect of media composition, either liquid or solid state, on the combined process of germination, outgrowth and vegetative growth of individually sorted untreated and heat treated B.

Firstly, we showed for wild type spores that rice broth was least supporting the growth and recovery of heat treated spores while rice agar plates provided comparable recovery as BHI broth, indicating that not only the composition but also the liquid or solid state of media effects the recovery of heat treated spores. Both heat treated and untreated B. More specifically, rice media increased heterogeneity and delayed outgrowth of untreated spores compared to BHI, and also a heat treatment had a limited additional effect on the behavior of surviving spores Warda et al.

Now we show that outgrowth from untreated single spores was slower in rice based media compared to BHI, but final counts for untreated single sorted spores on rice plates were In line with our previous observations, the time required for colony formation from untreated B. Comparative analysis of wild type and selected mutants lacking genes with putative roles in damage repair, showed different capacity to recover from heat stress compared to wild type.

The most pronounced effect was observed for a deletion mutant, lacking a membrane protein with C2C2 zinc finger BC This mutation resulted in reduction in recovery down to 3. The function of BC is unknown, but orthologs of its gene product can be found in many B. In eukaryotes, zinc finger containing proteins function in gene transcription, translation, mRNA trafficking, cytoskeleton organization, epithelial development, cell adhesion, protein folding, chromatin remodeling, and zinc sensing Laity et al.

In prokaryotes, zinc finger motifs C4 superfamily are found in proteins involved in DNA damage recognition, i. Notably, BC was not upregulated in vegetative cells of B. BC was found to be highly upregulated during germination and outgrowth of heat damaged B. Analysis of the B. The B. Furthermore, in B. In strains belonging to the B. It remains to be determined whether the observed increase in recovery of the individual cdnL mutants could be explained by cross regulation of the counterpart.

Both cdnL1 and cdnL2 genes are induced in vegetative cells in response to various environmental stresses, including salt and cold stress, whereas acid and oxidative stress specifically induced expression of cdnL1 and not cdnL2 Abee et al.

Our findings suggest partly overlapping functionalities of cdnL1 and cdnL2 in recovery and possibly repair of heat damage. Orthologs of BC are commonly found among B. Deletion of BC and BC, both encoding putative quaternary ammonium compound resistance proteins annotated as sugE , resulted in reduction in recovery of spores to 9.

Still, not all PSMR members have demonstrated drug resistance, e. However, application of rice media and BHI agar plates compared to BHI broth for sorted spores also revealed differences in recovery between media suggesting different requirements for recovery.

Particularly deletion of BC or BC resulted in reduced recovery on rice plates while spores of remaining seven deletion mutants showed improved recovery on rice plates compared to BHI broth Supplementary Figure S4. Apparently, high numbers of damaged spores were present in the surviving wild type and mutant spore population, but nevertheless, subtle effects of mutations in putative repair genes were noted, resulting in a shift from the fraction of mildly damaged to the fraction of severely damaged spores Warda et al.

Still, recovery of heat treated spores is a complex process conceivably involving many different systems, and more studies are required to elucidate the full repertoire of repair systems and the impact of matrix composition and its solid or liquid state on this process.

We have shown that recovery of heat treated B. The comparative analysis of the wild type and newly constructed deletion mutants provided new insights in the putative role of the deleted genes in the recovery of heat treated B. Performed the experiments: AW, MT. Analyzed the data: AW, MT. TIFN provided support in the form of salaries for authors [AW, MT, MNG, TA], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

FBR has no financial interest in any specific outcome of the study. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The project is funded by TI Food and Nutrition, a public—private partnership on precompetitive research in food and nutrition. The public partners are responsible for the study design, data collection and analysis, decision to publish, and preparation of the manuscript.

The private partners have contributed to the project through regular discussion. We would like to thank Clint van Melis and Yao Lu for their contribution in preliminary experiments. Abee, T. From transcriptional landscapes to the identification of biomarkers for robustness. Cell Fact. Adams, D. Google Scholar. Aguirre, J. A comparison of the effects of E-beam irradiation and heat treatment on the variability of Bacillus cereus inactivation and lag phase duration of surviving cells.

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Initial B. The vegetative form of B. In dry or acidic foods B. The heat resistance of the spores varies between strains and is strongly dependent on the food matrix. Common heat treatments, such as cooking or pasteurization, inactivate vegetative cells but are not sufficient to completely inactivate spores. The reduction of the competitive microbiota by heat treatment supports both the germination of the spores and the growth of vegetative cells. This site only uses cookies to offer you a better browsing experience.

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Schnellsuche Search advanced search. Bacillus cereus Bacillus B. Characteristics Initial B. Two types of foodborne disease are caused by B.

Cereulide is extremely resistant to heat, pH and proteolysis. Ingestion of the toxin intoxication causes nausea and vomiting within a few hours 0. The symptoms are mostly self-limiting within few days. Very rarely severe clinical cases are reported due to liver failure and brain edema.

Cereulide intoxication is frequently associated with the consumption of starchy, cooked food such as rice or pasta dishes.