The wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores produced in a two-step sporulation process depends on sporulation temperature but not on previous cell history (original) (raw)
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Food Microbiology, 2012
Although sporulation environmental factors are known to impact on Bacillus spore heat resistance, they are not integrated into predictive models used to calculate the efficiency of heating processes. This work reports the influence of temperature and pH encountered during sporulation on heat resistance of Bacillus weihenstephanensis KBAB4 and Bacillus licheniformis AD978 spores. A decrease in heat resistance (d) was observed for spores produced either at low temperature, at high temperature or at acidic pH. Sporulation temperature and pH maximizing the spore heat resistance were identified. Heat sensitivity (z) was not modified whatever the sporulation environmental factors were. A resistance secondary model inspired by the Rosso model was proposed. Sporulation temperatures and pHs minimizing or maximizing the spore heat resistance (T min(R) , T opt(R) , T max(R) , pH min(R) and pH opt(R) ) were estimated. The goodness of the model fit was assessed for both studied strains and literature data. The estimation of the sporulation temperature and pH maximizing the spore heat resistance is of great interest to produce spores assessing the spore inactivation in the heating processes applied by the food industry.
Effects of sporulation media and strain on thermal resistance of Bacillus cereus spores
International Journal of Food Science and Technology, 2007
Spores of Bacillus cereus strains ATCC 7004, ATCC 4342 and ATCC 9818 were produced in four sporulation media (Nutrient Agar supplemented with 1 ppm Mn2+, Fortified Nutrient Agar, Angelotti Medium and Milk Agar) and their percentages of sporulation and heat resistance parameters obtained in a wide temperature range were compared. In all conditions studied, high rates of sporulation were obtained. Clear differences among D-values for spores produced in the four media were observed. the medium which yielded the most resistant spores and the magnitude with which the sporulation medium affected D-values was different for each strain. z-Values of the three strains were not influenced by the medium used to obtain spores.
Comparative analysis of Bacillus weihenstephanensis KBAB4 spores obtained at different temperatures
International Journal of Food Microbiology, 2010
The impact of Bacillus weihenstephanensis KBAB4 sporulation temperature history was assessed on spore heat resistance, germination and outgrowth capacity at a temperature range from 7 to 30°C. Sporulation rate and efficiency decreased at low temperature, as cells sporulated at 12, 20 and 30°C with approximately 99% efficiency, whereas at 7°C and 10°C, a maximum 15% of sporulation was reached. Spores formed at 30°C showed the highest wet heat resistance at 95°C, with spores formed at 7 and 10°C displaying only survival of 15 min exposure at 70°C, indicating their low level heat resistance. RT-PCR analysis revealed expression of sporulation sigma factor sigG, and germinant receptor operons gerI, gerK, gerL, gerR, gerS, and (plasmidlocated) gerS2 to be activated in all sporulation conditions tested. Subsequent germination assays revealed a combination of inosine and L-Alanine to be very efficient, triggering over 99% of the spores to germinate, with spores obtained at 30°C showing the highest germination rates (99%). Notably, spores obtained at 12, 20 and 30°C, germinated at all tested temperatures, showing N 70% spore germination even at temperatures as low as 5°C. Less than 5% of spores obtained at 7 and 10°C showed a germination response. Furthermore, spores produced at 12, 20 and 30°C showed similar outgrowth effiency at these temperatures, indicating that low temperature sporulation history does not improve low temperature outgrowth performance. Insights obtained in sporulation and germination behaviour of B. weihenstephanensis KBAB4, in combination with the availability of its genome sequence, may contribute to our understanding of the behaviour of psychrotolerant spoilage and pathogenic Bacilli.
Heat activation and inactivation of bacterial spores. Is there an overlap?
2021
Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant ...
PLoS ONE, 2013
Spore-forming bacteria are a special problem for the food industry as some of them are able to survive preservation processes. Bacillus spp. spores can remain in a dormant, stress resistant state for a long period of time. Vegetative cells are formed by germination of spores followed by a more extended outgrowth phase. Spore germination and outgrowth progression are often very heterogeneous and therefore, predictions of microbial stability of food products are exceedingly difficult. Mechanistic details of the cause of this heterogeneity are necessary. In order to examine spore heterogeneity we made a novel closed air-containing chamber for live imaging. This chamber was used to analyze Bacillus subtilis spore germination, outgrowth, as well as subsequent vegetative growth. Typically, we examined around 90 starting spores/cells for $4 hours per experiment. Image analysis with the purposely built program ''SporeTracker'' allows for automated data processing from germination to outgrowth and vegetative doubling. In order to check the efficiency of the chamber, growth and division of B. subtilis vegetative cells were monitored. The observed generation times of vegetative cells were comparable to those obtained in well-aerated shake flask cultures. The influence of a heat stress of 85uC for 10 min on germination, outgrowth, and subsequent vegetative growth was investigated in detail. Compared to control samples fewer spores germinated (41.1% less) and fewer grew out (48.4% less) after the treatment. The heat treatment had a significant influence on the average time to the start of germination (increased) and the distribution and average of the duration of germination itself (increased). However, the distribution and the mean outgrowth time and the generation time of vegetative cells, emerging from untreated and thermally injured spores, were similar.
International Journal of Food Microbiology, 2010
The objective of this research was to study the rate of structural damage and survival of Bacillus sporothermodurans spores following treatment at high temperatures by determining the amount of Dipicolinic acid (DPA) and soluble protein leakage over time. A reference strain of B. sporothermodurans (DSM 10599) and a South African strain (UP20A) isolated from UHT milk were used. To determine the survival of spores at 130°C, spores were heated for 4, 8 and 12 min. To check the viability of spores plate counts were determined, while structural damage was determined using the Transmission Electron Microscopy. The filtrate of the heated spore suspension was analysed for the amount of DPA and soluble protein release due to heating. The amount of DPA released was quantified by HPLC analysis while the amount of soluble protein released from heated spores was quantified using the Bradford method. The log values of spore counts, released DPA and soluble proteins from triplicate experiments were analysed. The results of this study indicate that the inactivation of B. sporothermodurans spores during wet heat treatment is due to the penetration of hot moisture into the spore which then moistens the spore components, and inactivates enzymes, and because of the high water pressure, vital spore components such as proteins and DPA in solution leak out of the spore. Interestingly a vast majority of heated spores were inactivated before a significant amount of DPA was released. This research is the first to determine the effect of high temperature wet heat treatment on the structure of B. sporothermodurans spores and has given an insight regarding the mechanisms of destruction of B. sporothermodurans spores by wet heat.
Water Distribution in Bacterial Spores: A Key Factor in Heat Resistance
Food Biophysics, 2013
The role of water, its distribution and its implication in the heat resistance of dried spores was investigated using DSC (Differential Scanning Calorimetry). Bacillus subtilis spores equilibrated at different water activity levels were heat treated under strictly controlled conditions. The temperature was increased linearly in pans with different resistances to pressure. Data from the heat-related transitions occurring in the spores were recorded and spore viability was assessed at different stages during DSC. The thermodynamic transitions observed were related to the water status in the spores and spore survival. The results demonstrated that water still remained in the spore core when water activity was as low as 0.13. The first transition occurred at around 150°C and was assumed to be related to a mobile fraction of water from the outer layers of the spore. The second occurred at around 200°C, which could correspond to a fraction of water embedded in the spore core. Moreover, the results showed that spore destruction during heating was favored by the amount of water remaining in the spore. The changes in their structure were also evaluated by FTIR (Fourier Transform Infrared Spectroscopy). This work offers new understanding about the distribution of water in spores and presents new elements on the heat resistance of spores in relation to their water content.
Applied and Environmental Microbiology, 2001
Spores of Bacillus cereus were heated and recovered in order to investigate the effect of water activity of media on the estimated heat resistance (i.e., the D value) of spores. The water activity (ranging from 0.9 to 1) of the heating medium was first successively controlled with three solutes (glycerol, glucose, and sucrose), while the water activity of the recovery medium was kept near 1. Reciprocally, the water activity of the heating medium was then kept at 1, while the water activity of the recovery medium was controlled from 0.9 to 1 with the same depressors. Lastly, in a third set of experiments, the heating medium and the recovery medium were adjusted to the same activity. As expected, added depressors caused an increase of the heat resistance of spores with a greater efficiency of sucrose with respect to glycerol and glucose. In contrast, when solutes were added to the recovery medium, under an optimal water activity close to 0.98, a decrease of water activity caused a dec...