Physical Treatments to Control Clostridium botulinum Hazards in Food.

Clostridium botulinum produces Botulinum neurotoxins (BoNTs), causing a rare but potentially deadly type of food poisoning called foodborne botulism. This review aims to provide information on the bacterium, spores, toxins, and botulisms, and describe the use of physical treatments (e.g., heating, pressure, irradiation, and other emerging technologies) to control this biological hazard in food. As the spores of this bacterium can resist various harsh environmental conditions, such as high temperatures, the thermal inactivation of 12-log of C. botulinum type A spores remains the standard for the commercial sterilization of food products. However, recent advancements in non-thermal physical treatments present an alternative to thermal sterilization with some limitations. Low- (<2 kGy) and medium (3-5 kGy)-dose ionizing irradiations are effective for a log reduction of vegetative cells and spores, respectively; however, very high doses (>10 kGy) are required to inactivate BoNTs. High-pressure processing (HPP), even at 1.5 GPa, does not inactivate the spores and requires heat combination to achieve its goal. Other emerging technologies have also shown some promise against vegetative cells and spores; however, their application to C. botulinum is very limited. Various factors related to bacteria (e.g., vegetative stage, growth conditions, injury status, type of bacteria, etc.) food matrix (e.g., compositions, state, pH, temperature, aw, etc.), and the method (e.g., power, energy, frequency, distance from the source to target, etc.) influence the efficacy of these treatments against C. botulinum. Moreover, the mode of action of different physical technologies is different, which provides an opportunity to combine different physical treatment methods in order to achieve additive and/or synergistic effects. This review is intended to guide the decision-makers, researchers, and educators in using physical treatments to control C. botulinum hazards.

Walking dead: Permeabilization of heat-treated Geobacillus stearothermophilus ATCC 12980 spores under growth-preventing conditions.

Although heat treatment is probably the oldest and the most common method used to inactivate spores in food processes, the specific mechanism of heat killing of spores is still not fully understood. The purpose of this study is to investigate the evolution of the permeabilization and the viability of heat-treated spores during storage under growth-preventing conditions. Geobacillus stearothermophilus spores were heat-treated under various conditions of temperature and pH, and then stored under conditions of temperature and pH that prevent growth. Spore survival was evaluated by count plating immediately after heat treatment, and then during storage over a period of months. Flow cytometry analyses were performed to investigate the Syto 9 permeability of heat-treated spores. Sub-lethally heat-treated spores of G. stearothermophilus were physically committed to permeabilization after heat treatment. However, prolonged heat treatment may abolish the spore permeabilization and block heat-treated spores in the refractive state. However, viability loss and permeabilization during heat treatment seem to be two different mechanisms that occur independently, and the loss of permeabilization properties takes place at a much slower rate than spore killing. Under growth-preventing conditions, viable heat-treated spores presumably lose their viability due to the permeabilization phenomena, which makes them more susceptible to the action of adverse conditions precluding growth.

Elionurus tristis Essential Oil: GC-MS Analysis and Antioxidant and Antituberculosis Activities.

Essential oil was obtained in a yield 1.1%, w/w, by steam distillation of Elionurus tristis leaves from Madagascar. The chemical composition was analyzed qualitatively and quantitatively by GC-MS and GC-FID, respectively. To the best of our knowledge, this is the first chemical analysis of this essential oil. Seventy-three compounds were identified, corresponding to 94.9% of the total essential oil. The principal compounds were sesquiterpenes and the more represented were ß-gudjunene (18.4%), neoclovene (15.8%) and nootkatone (10.4%). Through a comparative study, we observed a large variability between the components of E. tristis essential oil and those from others species of the same genus. Evaluation of the antioxidant (ABTS and DPPH assays) and anti- tuberculosis activities of the essential oil showed weak antioxidant potency but an interesting anti-tuberculosis activity with a MIC of 32 mg/L. This activity prompted us to evaluate individually the major components for the treatment of tuberculosis.

Die another day: Fate of heat-treated Geobacillus stearothermophilus ATCC 12980 spores during storage under growth-preventing conditions.

Geobacillus stearothermophilus spores are recognized as one of the most wet-heat resistant among aerobic spore-forming bacteria and are responsible for 35% of canned food spoilage after incubation at 55 °C. The purpose of this study was to investigate and model the fate of heat-treated survivor spores of G. stearothermophilus ATCC 12980 in growth-preventing environment. G. stearothermophilus spores were heat-treated at four different conditions to reach one or two decimal reductions. Heat-treated spores were stored in nutrient broth at different temperatures and pH under growth-preventing conditions. Spore survival during storage was evaluated by count plating over a period of months. Results reveal that G. stearothermophilus spores surviving heat treatment lose their viability during storage under growth-preventing conditions. Two different subpopulations were observed during non-thermal inactivation. They differed according to the level of their resistance to storage stress, and the proportion of each subpopulation can be modulated by heat treatment conditions. Finally, tolerance to storage stress under growth-preventing conditions increases at refrigerated temperature and neutral pH regardless of heat treatment conditions. Such results suggest that spore inactivation due to heat treatment could be completed by storage under growth-preventing conditions.

Effect of pH on Thermoanaerobacterium thermosaccharolyticum DSM 571 growth, spore heat resistance and recovery.

Thermophilic spore-forming bacteria are potential contaminants in several industrial sectors involving high temperatures (40-65 °C) in the manufacturing process. Among those thermophilic spore-forming bacteria, Thermoanaerobacterium thermosaccharolyticum, called "the swelling canned food spoiler", has generated interest over the last decade in the food sector. The aim of this study was to investigate and to model pH effect on growth, heat resistance and recovery abilities after a heat-treatment of T. thermosaccharolyticum DSM 571. Growth and sporulation were conducted on reinforced clostridium media and liver broth respectively. The highest spore heat resistances and the greatest recovery ability after a heat-treatment were obtained at pH condition allowing maximal growth rate. Growth and sporulation boundaries were estimated, then models using growth limits as main parameters were extended to describe and quantify the effect of pH on recovery of injured spores after a heat-treatment. So, cardinal values were used as a single set of parameters to describe growth, sporulation and recovery abilities. Besides, this work suggests that T. thermosaccharolyticum preserve its ability for germination and outgrowth after a heat-treatment at a low pH where other high resistant spore-forming bacteria like Geobacillus stearothermophilus are unable to grow.

Modeling the behavior of Geobacillus stearothermophilus ATCC 12980 throughout its life cycle as vegetative cells or spores using growth boundaries.

Geobacillus stearothermophilus is recognized as one of the most prevalent micro-organism responsible for flat sour in the canned food industry. To control these highly resistant spore-forming bacteria, the heat treatment intensity could be associated with detrimental conditions for germination and outgrowth. The purpose of this work was to study successively the impact of temperature and pH on the growth rate of G. stearothermophilus ATCC 12980, its sporulation ability, its heat resistance in response to various sporulation conditions, and its recovery ability after a heat treatment. The phenotypic investigation was carried out at different temperatures and pHs on nutrient agar and the heat resistance was estimated at 115 °C. The greatest spore production and the highest heat resistances were obtained at conditions of temperature and pH allowing maximal growth rate. The current observations also revealed that growth, sporulation and recovery boundaries are close. Models using growth boundaries as main parameters were extended to describe and quantify the effect of temperature and pH throughout the life cycle of G. stearothermophilus as vegetative cells or as spore after a heat treatment and during recovery.

Metabolic phenotypes of Saccharomyces cerevisiae mutants with altered trehalose 6-phosphate dynamics.

In Saccharomyces cerevisiae, synthesis of T6P (trehalose 6-phosphate) is essential for growth on most fermentable carbon sources. In the present study, the metabolic response to glucose was analysed in mutants with different capacities to accumulate T6P. A mutant carrying a deletion in the T6P synthase encoding gene, TPS1, which had no measurable T6P, exhibited impaired ethanol production, showed diminished plasma membrane H⁺-ATPase activation, and became rapidly depleted of nearly all adenine nucleotides which were irreversibly converted into inosine. Deletion of the AMP deaminase encoding gene, AMD1, in the tps1 strain prevented inosine formation, but did not rescue energy balance or growth on glucose. Neither the 90%-reduced T6P content observed in a tps1 mutant expressing the Tps1 protein from Yarrowia lipolytica, nor the hyperaccumulation of T6P in the tps2 mutant had significant effects on fermentation rates, growth on fermentable carbon sources or plasma membrane H⁺-ATPase activation. However, intracellular metabolite dynamics and pH homoeostasis were strongly affected by changes in T6P concentrations. Hyperaccumulation of T6P in the tps2 mutant caused an increase in cytosolic pH and strongly reduced growth rates on non-fermentable carbon sources, emphasizing the crucial role of the trehalose pathway in the regulation of respiratory and fermentative metabolism.