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Bacteria are constantly faced to stress situations in their ecological niches, the food and the host gastrointestinal tract. The capacity to detect and respond to surrounding changes is crucial for bacterial pathogens to survive or grow in changing environments. To this purpose, cells have evolved various sophisticated networks designed to protect against stressors or repair damage caused by them. Challenges can occur during production of foods when subjected to processing, and after food ingestion when confronted with host defensive barriers. Some pathogenic bacteria have shown the capacity to develop stable resistance against extreme conditions within a defined genomic context and a limited number of generations. On the other hand, bacteria can also respond to adverse conditions in a transient manner, through the so-called stress tolerance responses. Bacterial stress tolerance responses include both structural and physiological modifications in the cell and are mediated by complex genetic regulatory machinery. Major aspects in the adaptive response are the sensing mechanisms, the characterization of cell defensive systems, such as the operation of regulatory proteins (e.g. RpoS), the induction of homeostatic and repair systems, the synthesis of shock response proteins, and the modifications of cell membranes, particularly in their fatty acid composition and physical properties. This article reviews certain strategies used by food-borne bacteria to respond to particular stresses (acid, cold stress, extreme pressure) in a permanent or transient manner and discusses the implications that such adaptive responses pose for food safety. [ABSTRACT FROM AUTHOR]

Food raw materials used in refrigerated processed foods of extended durability (REPFEDs) manufactured in France were surveyed for Clostridium botulinum types A, B and E using PCR–Enzyme-linked Immunosorbent assay (PCR–ELISA) and mouse bioassay for detection respectively of cells and toxins in enrichment broth. Portions of 25 to 50 g of food were analysed. A total of 8 out of the 102 samples of fish and shellfish, 12 out of the 143 samples of meat and poultry, 1 out of the 62 samples of aroma, sauce and gravy, 4 out of the 25 samples of thickening agents, 3 out of the 26 samples of dehydrated dairy ingredients, and none of the 65 samples of spices, herbs and dehydrated mushroom were positive for C. botulinum in PCR–ELISA, i.e., 6.6% of all the samples tested. The 28 positive samples comprised 10 type A, 10 type B, 4 with both types A and B, and 4 undetermined by PCR typing. No sample positive for type E was detected. Of the 28 samples positive in PCR–ELISA, 15 were also positive in the mouse bioassay. The MPN count was between 1 and 3 C. botulinum/kg of food, which is similar to or in the lower range of values reported in the literature. [Copyright &y& Elsevier]

The growth of proteolytic Clostridium botulinum from spore inocula and changes in spore counts in mushroom, broccoli, and potato purées were monitored. Four strains of proteolytic C. botulinum types A and B were inoculated separately at approximately 10[sup 4] spores per ml in nutrient broth and vegetable purées incubated at 15, 20, and 30°C for up to 52 days. The times for the cell populations to increase 1,000-fold (T[sub 1,000]) in the tested vegetables (1 to 5 days at 30°C, 3 to 16 days at 20°C, 7 to >52 days at 15°C) were similar to those for meat or fish. Only temperature significantly influenced growth rate. In contrast, the lag phase depended on the strains and media tested, in addition to temperature. Lag times and T[sub 1,000]s for proteolytic C. botulinum were longer for potato and broccoli purées than for mushroom purée. These differences were not related to different phs or redox potentials. The germination level, evaluated as the decrease in the spore count, was low. The addition of a germinant mixture (L-cysteine, L-alanine, and sodium lactate) to some strains inoculated in vegetable purées resulted in an increase in germination, suggesting a lack of germination-triggering agents in the vegetable purées. [ABSTRACT FROM AUTHOR]

Abstract: Consequences of climate change on the ecology of pathogens are difficult to forecast. However changes affecting microorganisms will likely involve already known evolution or adaptation mechanisms. Bacillus cereus is a frequent cause of foodborne poisonings and is known as a soil borne bacterium. B. cereus may represent an interesting model to study the impact of climate change on foodborne pathogens. The B. cereus group (or B. cereus sensu lato) displays a wide diversity of strains recently distributed in seven major phylogenetic groups. B. cereus growth domains range from psychrotrophic to nearly thermophilic. Current climate selects B. cereus distribution: psychrotrophes are more common in cold areas, while mesophiles prevail in tropical soils. In response to external signals, B. cereus may adapt to changing environments by varied mechanisms. Some illustrations of the signal transduction systems (two-component systems, alternative σ factors) and of the mechanisms of B. cereus adaptation to major environmental factors (temperature, carbon source, redox potential and pH) are proposed. The environment of sporulation has an impact on spore properties; heat resistance is positively correlated with sporulation temperature. Surveillance needed to detect changes in the epidemiology of B. cereus foodborne poisonings as a consequence of climate change is discussed. [Copyright &y& Elsevier]

Spore-forming bacteria are able to grow under a wide range of environmental conditions, to form biofilms and to differentiate into resistant forms: spores. This resistant form allows their dissemination in the environment; consequently, they may contaminate raw materials. Sporulation can occur all along the food chain, in raw materials, but also in food processes, leading to an increase in food contamination. However, the problem of sporulation during food processing is poorly addressed and sporulation niches are difficult to identify from the farm to the fork. Sporulation is a survival strategy. Some environmental factors are required to trigger this differentiation process and others act by modulating it. The efficiency of sporulation is the result of the combined effects of these two types of factors on vegetative cell metabolism. This paper aims to explain and help identify sporulation niches in the food chain, based on features of spore-former physiology. [ABSTRACT FROM AUTHOR]

Fresh produce has been a growing cause of food borne outbreaks world-wide prompting the need for safer production practices. Yet fresh produce agrifood systems are diverse and under constraints for more sustainability. We analyze how measures taken to guarantee safety interact with other objectives for sustainability, in light of the diversity of fresh produce agrifood systems. The review is based on the publications at the interface between fresh produce safety and sustainability, with sustainability defined by low environmental impacts, food and nutrition security and healthy life. The paths for more sustainable fresh produce are diverse. They include an increased use of ecosystem services to e.g. favor predators of pests, or to reduce impact of floods, to reduce soil erosion, or to purify run-off waters. In contrast, they also include production systems isolated from the environment. From a socio-economical view, sustainability may imply maintaining small tenures with a higher risk of pathogen contamination. We analyzed the consequences for produce safety by focusing on risks of contamination by water, soil, environment and live stocks. Climate change may increase the constraints and recent knowledge on interactions between produce and human pathogens may bring new solutions. Existing technologies may suffice to resolve some conflicts between ensuring safety of fresh produce and moving towards more sustainability. However, socio-economic constraints of some agri-food systems may prevent their implementation. In addition, current strategies to preserve produce safety are not adapted to systems relying on ecological principles and knowledge is lacking to develop the new risk management approaches that would be needed. [ABSTRACT FROM AUTHOR]

Bacillus cereus sensu lato is composed of a set of ubiquitous strains including human pathogens that can survive a range of food processing conditions, grow in refrigerated food, and sometimes cause food poisoning. We previously identified the two-component system CasK/R that plays a key role in cold adaptation. To better understand the CasK/R-controlled mechanisms that support low-temperature adaptation, we performed a transcriptomic analysis on the ATCC 14579 strain and its isogenic ∆ casK/R mutant grown at 12 °C. Several genes involved in fatty acid (FA) metabolism were downregulated in the mutant, including desA and desB encoding FA acyl-lipid desaturases that catalyze the formation of a double-bond on the FA chain in positions ∆5 and ∆10, respectively. A lower proportion of FAs presumably unsaturated by DesA was observed in the ΔcasK/R strain compared to the parental strain while no difference was found for FAs presumably unsaturated by DesB. Addition of phospholipids from egg yolk lecithin rich in unsaturated FAs, to growth medium, abolished the cold-growth impairment of ΔcasK/R suggesting that exogenous unsaturated FAs can support membrane-level modifications and thus compensate for the decreased production of these FAs in the B. cereus ∆ casK/R mutant during growth at low temperature. Our findings indicate that CasK/R is involved in the regulation of FA metabolism, and is necessary for cold adaptation of B. cereus unless an exogenous source of unsaturated FAs is available. [ABSTRACT FROM AUTHOR]

The commercial potential of high pressure and thermal processing (HPTP) was investigated against Alicyclobacillus acidoterrestris spores in commercial acidic apple juice beverage and in acidified and neutral potassium buffers. With starting spore counts prior to treatments being 6.5 and 7.2 log 10 respectively for strains AJA 66 (D 90°C 15.4 min) and ATCC 49025 (D 90°C 8.5 min), HPTP at 600 MPa at 80 °C for 3 min provided an optimal treatment with spore viability reduced below the detection limit for both strains. HPTP at 80 °C for 1 min and HPTP at 70 °C for 3 min achieved 4.1–4.5 log 10 CFU/mL reduction. HPTP at 70 °C for 1 min reduced the number of viable spores by 2.0–2.5-log 10 CFU/mL. Flow cytometry revealed the presence of membrane-compromised spores among culturable spores following HPTP and heat alone treatments at different temperatures. Electron microscopy clearly showed the efficiency of HPTP with crushed or hollow spores predominating after treatments. No correlation between HPTP susceptibility and genetic diversity was observed for two genotypes of A. acidoterrestris spores. The treatment combination provides a promising option for industrial utility since it requires lower heat and processing time. • High pressure thermal processing (HPTP) effectively killed A.acidoterrestris spores • HPTP effectiveness was time and temperature dependent • HPTP effectively inactivated spores from two diverse A. acidoterrestris genotypes • HPTP killed >4 and 6.2 log 10 of the spores at 70 °C and 80 °C in 3 min, respectively • Membrane damages of HPTP-treated spores observed with flow cytometry, SEM and TEM [ABSTRACT FROM AUTHOR]