Effect of water activities of heating and recovery media on apparent heat resistance of Bacillus cereus spores

Effects of spore purity on the wet heat resistance of Clostridium perfringens, Bacillus cereus and Bacillus subtilis spores

Heat resistance of spores of Clostridium perfringens 8238 (Hobbs Serotype 2), Bacillus cereus NCTC 11143 (4810/72), and Bacillus subtilis PS533, an isogenic derivative of strain PS832 (a 168 strain) was determined in ground beef at 95 °C. Spore purification was by centrifugation and washing with sterile distilled water (dH2O), followed by sonication and then Histodenz centrifugation for B. subtilis and C. perfringens, and centrifugation and washing with sterile dH2O followed by Histodenz centrifugation for B. cereus. Bags containing inoculated beef samples were submerged in a temperature-controlled water bath and held at 95 °C for predetermined lengths of time. Surviving spore populations were enumerated by plating on mannitol egg yolk polymyxin agar (MYP) agar plates for B. cereus and B. subtilis, and on tryptose-sulfite-cycloserine agar (TSC) agar plates for C. perfringens. Survivor curves were fitted to linear, linear with tail, and Weibull models using the USDA Integrated Pathogen Modeling Program (IPMP) 2013 software. The Weibull model provided a relatively better fit to the data since the root mean square error (RMSE), mean square error (MSE), sum of squared errors (SSE), and Akaike information criterion (AIC) values were lower than the values obtained using the linear or the linear with tail models. Additionally, the Weibull model accurately predicted the observed D-values at 95 °C for the three spore-formers since the accuracy factor (Af) values ranged from 1.03 to 1.08 and the bias factor (Bf) values were either 1.00 or 1.01. Times at 95 °C to achieve a 3-log reduction decreased from 206 min for C. perfringens spores purified with water washes alone to 191 min with water washes followed by sonication and Histodenz centrifugation, from 7.9 min for B. cereus spores purified with water washes alone to 1.4 min with water washes followed by Histodenz centrifugation, and from 20.6 min for B. subtilis spores purified with water washes alone to 6.7 min for water washes followed by sonication and Histodenz centrifugation. Thermal-death-time values reported in this study will assist food processors to design thermal processes to guard against bacterial spores in cooked foods. In addition, clearly spore purity is an additional factor in spore wet heat resistance, although the cause of this effect is not clear.

Joint effect of heat, pH and grape extract on Bacillus cereus spores survival in a rice solution

Rice due to its high carbohydrate content, is an ideal medium for Bacillus cereus growth, a spore-producing microorganism. The objective of this study was to determine the antimicrobial activity of a grape extract in combination with heat treatments and different pH against B. cereus spores in a rice solution. The survivor data obtained were fitted to the Weibull survival function, and the values of parameters a and b (scale and shape indexes, respectively) were determined. Results showed that the grape extract affected the survival of B. cereus spores at 90 °C and 95 °C, reaching greater logarithmic reductions in acidic pH values. This behaviour was reflected in a parameter of the Weibull survival function which decreased as the temperature increased and at acidic pH values. In addition, a secondary model was developed by relating the logarithm of a to the independent variables (temperature and pH). A global model relating B. cereus inactivation with temperature and pH was developed, and validated by calculating the accuracy factor. The results demonstrate the usefulness of grape extract as a by-product, which can be used as an additional control measure for rice, especially when combined with mild heat treatments and acidic pH values.

Persistence of surrogates for high consequence viral and bacterial pathogens in a pilot-scale activated sludge treatment system

The persistence of high consequence public health pathogens in a wastewater treatment system can significantly impact worker safety, as well as the public and downstream water bodies, particularly if the system is forced to shut down the treatment processes. This study utilizes organism viability to compare the persistence of three pathogen surrogates in wastewater using a pilot-scale activated sludge treatment (AST) system, operated to mimic treatment processes of large-scale plants. Bacillus globigii spores, surrogate for Bacillus anthracis, persisted in the AST system for at least a 50-day observation period leading to a possible steady condition far beyond the solid retention time for sludge particles. MS2 bacteriophage, surrogate for Poliovirus and other non-enveloped enteric viruses, was observed for up to 35 days after introduction, which largely and expectedly correlated to the measured solid retention time. Phi-6 bacteriophage, a surrogate for Ebola virus and other enveloped viruses, was detected for no more than 4 days after introduction, even though the AST system was operated to provide three times slower solids removal than for the other surrogates. This suggests Phi-6 is subject to inactivation under AST conditions rather than physical removal. These results may suggest similar persistence for the surrogated pathogens, leading to appropriate consequence management actions.

Development of a predictive model of the microbial inactivation of L. monocytogenes during low thermal treatment of fruit juices in combination with carvacrol as aroma compound

Mild heat treatment of fruit juices in combination with natural aroma compounds has been reported as an alternative to conventional pasteurization to better preserve their nutritional value. However, its antimicrobial efficiency varies from one juice to another. This study aims at developing a secondary predictive model of microbial inactivation scale during such combined process. Carvacrol was used as aroma compound and acid-adapted L. monocytogenes as target microorganism. The inactivation kinetics of this bacteria were followed in simulated fruit juices using a Central Composite Design with pH (2-6), °Brix (0–24), temperature (55–65 °C), and carvacrol concentration (0–60 μL/L) as independent variables. Curves were fitted to the Weibull inactivation model, and data collected used to generate two predictive models of the inactivation scale parameter through multiple regression analysis following an empirical and a mechanistic (based on Gamma concept) approach. The best of the two models was then validated using real fruit (orange, pineapple, and watermelon) juices. The empirical model where only the four variables tested were considered showed a lower statistical performance compared to the mechanistic model where octanol-water partition coefficient (Ko/w) and vapour pressure (Vp) of carvacrol at the treatment temperature were integrated (R² 0.6 and 0.9; Accuracy factor 1.5 and 1.3; Sum of Squared Error 3.6 and 1.1, respectively). No significant difference was observed between inactivation scale values obtained with real juices and the predicted values calculated using this mechanistic model. The Ko/w and Vp of the aroma compound used are key parameters that determine the efficiency of the above-described combined treatment.

pH and Brix of fruit juices determine L. monocytogenes mild heat inactivation

Carvacrol supplementation enhances mild heat tolerance of Listeria monocytogenes

This carvacrol effect is determined by its partition coefficient and vapour pressure

Consideration of these two physicochemical parameters increases model prediction.

Modeling the combined effect of temperature, pH, acetic and lactic acid concentrations on the growth/no growth interface of acid-tolerant Bacillus spores

The application of minimal processing technologies has led to increased spoilage incidents in low-acid pasteurized sauces due to the outgrowth of acid-tolerant spore-forming spoilage bacteria (ATSSB). Controlling the germination and subsequent growth of ATSSB spores is vital to enhance the ambient storage stability of pasteurized sauces. This study developed and validated a set of growth/no growth (G/NG) models for spores of two ATSSB strains (Bacillus velezensis and Bacillus subtilis subsp. subtilis) isolated from pasteurized sauces. The G/NG data at two levels of temperature (22 and 30 °C) were collected in Nutrient Broth (a_w = 0.98 adjusted with NaCl) by a full factorial design with five equidistant levels of pH (4.4-5.6), four concentrations of total acetic acid (0.0-0.3% (w/w)), and four concentrations of total lactic acid (0.00-1.00% (w/w)). The growth, starting from heat-treated (10 min 80 °C) spores, of each strain was assessed under 160 combinations by regular optical density measurements during three months. Twelve replicates were made for each combination. The developed models demonstrate that without organic acids even the lowest pH (4.4) allows a high growth possibility of the ATSSB spores, while acetic and lactic acids exhibit a significant antibacterial activity, which can be enhanced at decreased pH. The growth starting from B. subtilis spores can be inhibited for at least three months with 1.0% (w/w) total lactic acid in the water phase at both temperatures, which was not the case for B. velezensis, while 0.3% acetic acid achieves a full inhibition on both strains at 22 °C. With a combination of 0.3% acetic acid and 0.7% lactic acid, no growth should occur in the investigated range. This research is one of the first studies exploring the feasibility of ambient storage for low-acid pasteurized sauces eliminating preservatives such as benzoic and sorbic acids, and proves the synergistic effect of decreased pH and the presence of acetic and lactic acids on inhibiting bacterial growth from ATSSB spores.

Use of Pelleted Diets in Commercially Farmed Decapods during Juvenile Stages: A Review

The increasing market demand for decapods has led to a considerable interest in cultivating decapod species at a larger scale. Following the development of hatchery technologies, most research has focused on the development of formulated feeds for commercially farmed decapods once they enter the juvenile stages. The use of formulated feed for decapods at a commercial scale is still in the early stages. This is probably because of the unique feeding behavior that decapods possess: being robust, slow feeders and bottom dwellers, their feeding preferences change during the transition from pelagic larvae to benthic juveniles as their digestive systems develop and become more complex. The current practice of decapod aquaculture involves the provision of juveniles with food such as natural diet, live feed, and formulated feed. Knowledge of nutrient requirements enables diets to be better formulated. By manipulating the levels of proteins and lipids, a formulated feed can be expected to lead to optimal growth in decapods. At the same time, the pellet's physical characteristics are important factors to be considered upon formulating commercially farmed decapod feeds, considering the unique feeding behavior of the decapod. However, most published studies on decapod nutrition lack data on the physical characteristics of the feed types. Thus, it is difficult to establish a standard feed formulation that focuses on the physical pellet properties. Moreover, careful consideration must be given to the feeding behavior of species, as decapods are known as bottom feeders and are robust in terms of handling feed. Information on the pellet forms, diet composition, and unique feeding behaviors in commercially farmed decapods is gathered to suggest potential better formulated diets that can optimize growth and reproduction. Thus, the purpose of this review is to summarize the information that has been published to date and to come up with suggestions on ways to improve the feed formulation in decapods that comply with their feeding behavior and nutrient requirements. Further research is needed to explore the potential of the pelleted feed at the adult stage so the decapod can take full advantage of the nutrients present in the pellets.

Effect of temperature and soluble solid on Bacillus subtilis and Bacillus licheniformis spore inactivation and quality degradation of pineapple juice

Bacillus subtilis and Bacillus licheniformis spores can survive processing temperatures used in the thermal processes of high-acid foods. Therefore, this study investigated the thermal inactivation of B. subtilis and B. licheniformis spores in pineapple juice at different temperatures (85-100°C) and soluble solids (SS, 11-30°Brix). The quality of juices and microbial loads after the thermal treatments during storage at 4 °C for 35 days was then checked. A linear decrease in D-value was observed with increasing temperature of treatment. Furthermore, the D-values determined in pineapple juice were: D_90°C=13.2 ± 0.5 mins, D_95°C = 6.8 ± 0.9 mins and D_100°C = 2.1 ± 1.7 mins for B. subtilis spores, and D_85°C = 16.6 ± 0.4 mins, D_90°C = 7.6 ± 0.5 mins and D_95°C = 3.6 ± 1.5 min, for B. licheniformis. Generally, the susceptibility of the bacteria to soluble solid change was affected by the interaction between temperature, SS and strain. In addition, pasteurization processes of ≥95°C for ≥33.8 mins was needed to ensure a recommended 5-log reduction of B. subtilis spores and limit vitamin C degradation of pineapple juice within three-week of storage at 4 °C.

Guidance on validation of lethal control measures for foodborne pathogens in foods

Food manufacturers are required to obtain scientific and technical evidence that a control measure or combination of control measures is capable of reducing a significant hazard to an acceptable level that does not pose a public health risk under normal conditions of distribution and storage. A validation study provides evidence that a control measure is capable of controlling the identified hazard under a worst-case scenario for process and product parameters tested. It also defines the critical parameters that must be controlled, monitored, and verified during processing. This review document is intended as guidance for the food industry to support appropriate validation studies, and aims to limit methodological discrepancies in validation studies that can occur among food safety professionals, consultants, and third-party laboratories. The document describes product and process factors that are essential when designing a validation study, and gives selection criteria for identifying an appropriate target pathogen or surrogate organism for a food product and process validation. Guidance is provided for approaches to evaluate available microbiological data for the target pathogen or surrogate organism in the product type of interest that can serve as part of the weight of evidence to support a validation study. The document intends to help food manufacturers, processors, and food safety professionals to better understand, plan, and perform validation studies by offering an overview of the choices and key technical elements of a validation plan, the necessary preparations including assembling the validation team and establishing prerequisite programs, and the elements of a validation report.

The Bacillus cereus Food Infection as Multifactorial Process

The ubiquitous soil bacterium Bacillus cereus presents major challenges to food safety. It is responsible for two types of food poisoning, the emetic form due to food intoxication and the diarrheal form emerging from food infections with enteropathogenic strains, also known as toxico-infections, which are the subject of this review. The diarrheal type of food poisoning emerges after production of enterotoxins by viable bacteria in the human intestine. Basically, the manifestation of the disease is, however, the result of a multifactorial process, including B. cereus prevalence and survival in different foods, survival of the stomach passage, spore germination, motility, adhesion, and finally enterotoxin production in the intestine. Moreover, all of these processes are influenced by the consumed foodstuffs as well as the intestinal microbiota which have, therefore, to be considered for a reliable prediction of the hazardous potential of contaminated foods. Current knowledge regarding these single aspects is summarized in this review aiming for risk-oriented diagnostics for enteropathogenic B. cereus.

Development of Bacterial Spore Pouches as a Tool to Evaluate the Sterilization Efficiency-A Case Study with Microwave Sterilization Using Clostridium sporogenes and Geobacillus stearothermophilus

In this study, novel spore pouches were developed using mashed potato as a food model inoculated with either Geobacillus stearothermophilus or Clostridium sporogenes spores. These spore pouches were used to evaluate the sterilization efficiency of Coaxially induced microwave pasteurization and sterilization (CiMPAS) as a case study. CiMPAS technology combines microwave energy (915 MHz) along with hot water immersion to sterilize food in polymeric packages. The spore pouches were placed at pre-determined specific locations, especially cold spots in each food tray before being processed using two regimes (R-121 and R-65), which consisted of 121 °C and 65 °C at 12 and 22 kW, respectively, followed by recovery and enumeration of the surviving spores. To identify cold spots or the location for inoculation, mashed potato was spiked with Maillard precursors and processed through CiMPAS, followed by measurement of lightness values (*L-values). Inactivation equivalent to of 1-2 Log CFU/g and >6 Log CFU/g for Geobacillus stearothermophilus and Clostridium sporogenes spores, respectively was obtained on the cold spots using R-121, which comprised of a total processing time of 64.2 min. Whereas, inactivation of <1 and 2-3 Log CFU/g for G. stearothermophilus and C. sporogenes spores, respectively on the cold spots was obtained using R-65 (total processing time of 68.3 min), whereas inactivation of 1-3 Log CFU/g of C. sporogenes spores was obtained on the sides of the tray. The results were reproducible across three processing replicates for each regime and inactivation at the specific locations were clearly distinguishable. The study indicated a strong potential to use spore pouches as a tool for validation studies of microwave-induced sterilization.

Influence of water activity on the heat resistance of Salmonella enterica in selected low-moisture foods

Low-moisture foods (LMF with water activity, a_w < 0.85) including pet foods and black pepper powder have consistently been associated with foodborne disease caused by Salmonella enterica. Increased heat resistance and prolonged survival at low-moisture conditions, however, remain major challenges to achieve effective inactivation of Salmonella in low-moisture foods. At low water activity (a_w) conditions, heat resistance of Salmonella is greatly enhanced when compared to high a_w conditions. This study aimed to quantify the effect of a_w on the heat resistance of Salmonella enterica in pet food pellets and black pepper powder. Pet food pellets were inoculated with two strains of heat resistant S. enterica and black pepper powder was inoculated with a 5-strain cocktail of Salmonella. Both inoculated food samples were equilibrated at 0.33, 0.54, and 0.75 a_w in controlled humidity chambers. Inoculated pet food pellets and black pepper powder in closed aluminum cells were heat treated at specific temperatures for selected times. The results showed that the Weibull model fitted well the inactivation data. At a specific temperature, the rate of inactivation increased with the increase in the a_w from 0.33 to 0.75, and the 3-log reduction times decreased for Salmonella in both food samples with the increase in a_w. Water adsorption isotherms of pet food pellets and black pepper powder at initial and treatment temperatures were developed to understand the change in a_w during heat treatments. The change in a_w during heat treatment was dependent on the type of food matrix, which possibly influenced the thermal inactivation of Salmonella in pet food pellets and black pepper powder. The quantitative analysis of heat reduction of Salmonella with respect to a_w aids in selection of the appropriate initial a_w to develop effective heat treatment protocols for adequate reduction of Salmonella in pet foods and black pepper powder.

Influence of aseptic surge tank venting on equipment sterilization

Abstract Aseptic surge tank (AST) systems are applied to aseptic production in order to store sterile product until aseptic filling, maintaining the commercial sterility condition achieved from previous production steps. To avoid microbial recontamination of the product, a sterility condition must be achieved in the aseptic tank system through the application of a heating, venting, and sterilization cycle. This cycle must follow specific validation protocols to ensure operational integrity - FDA 21 CFR Part 113.40g (ii). The demand for larger capacity systems and the implication of this volume increase on sterilization efficiency require a review of results obtained from current validation protocols. The purpose of this work was to evaluate aseptic surge tank’s venting cycles, studying internal pressure and temperature distribution to better understand this operation and its efficiency. Tests carried out at an industrial setting showed that the venting cycle was insufficient, with 13%-23% of air remaining inside the tank. Consequently, the subsequent sterilization process was not conducted under saturated steam condition. This different condition may change the kinetics for thermal destruction of microorganism spores from a moist heat state to a drier state in which its thermal resistance is higher. This finding raises a question regarding the true efficacy of the sterilization process and validation protocols currently used by the industry. The apparent success of current sterilization processes could be due to the application of excessive temperature and longer times. New operational and validation criteria will result in improvements in product integrity protection and operational cost reductions.

Life from the ashes: survival of dry bacterial spores after very high temperature exposure

We found that spores of Bacillus amyloliquefaciens rank amongst the most resistant to high temperatures with a maximum dry heat tolerance determined at 420 °C. We found that this extreme heat resistance was also maintained after several generations suggesting that the DNA was able to replicate after exposure to these temperatures. Nonetheless, amplifying the bacterial DNA using BOXA1R and (GTG)₅ primers was unsuccessful immediately after extreme heating, but was successful after incubation of the heated then cooled spores. Moreover, enzymes such as amylases and proteases were active directly after heating and spore regeneration, indicating that DNA coding for these enzymes were not degraded at these temperatures. Our results suggest that extensive DNA damage may occur in spores of B. amyloliquefaciens directly after an extreme heat shock. However, the successful germination of spores after inoculation and incubation indicates that these spores could have a very effective DNA repair mechanism, most likely protein-based, able to function after exposure to temperatures up to 420 °C. Therefore, we propose that B. amyloliquefaciens is one of the most heat resistant life forms known to science and can be used as a model organism for studying heat resistance and DNA repair. Furthermore, the extremely high temperature resistivity of these spores has exceptional consequences for general methodology, such as the use of dry heat sterilization and, therefore, virtually all studies in the broad area of high temperature biology.

Evaluation of an environmentally sustainable UV-assisted water treatment system for the removal of Bacillus globigii spores in water

Development of greener water treatment technologies is important for the production of safe drinking water and water security applications, such as decontamination. Chlorine assisted disinfection is common and economical, but can generate disinfection byproducts (DBPs) that may be of health concern. DBPs are formed due to the reaction of chlorine with naturally occurring organic and inorganic substances in water. Currently, various innovative technologies are being developed as alternative approaches for preventing DBPs during water treatment. In this study, we evaluated the effectiveness of a novel combination of high efficiency flow filtration and UV disinfection treatment system for the removal of Bacillus globigii (B. globigii) spores in water. The filtration system consists of a charged membrane filter (CMF) that not only helps to remove suspended particles but also reduces the impact of other impurities including bio organisms. In order to get most performance details, the CMF was evaluated at clean, half-life, and end of life (EOL) conditions along with 100% UV transmittance (UVT). In addition, the effectiveness of the UV system was evaluated as a stand alone system at 100% and 70% EOL intensity. The study was conducted at the US EPA's Test and Evaluation (T&E) Facility in Cincinnati, OH, using B. globigii, a surrogate for B. anthracis spores. This non-chemical environmentally-friendly CMF/UV combination system and the stand alone UV unit showed greater than 6.0 log removal of B. globigii during the tests.

Thermal Inactivation Kinetics of Sporolactobacillus nakayamae Spores, a Spoilage Bacterium Isolated from a Model Mashed Potato-Scallion Mixture

Sporolactobacillus species have been occasionally isolated from spoiled foods and environmental sources. Thus, food processors should be aware of their potential presence and characteristics. In this study, the heat resistance and influence of the growth and recovery media on apparent heat resistance of Sporolactobacillus nakayamae spores were studied and described mathematically. For each medium, survivor curves and thermal death curves were generated for different treatment times (0 to 25 min) at different temperatures (70, 75, and 80°C) and Weibull and first-order models were compared. Thermal inactivation data for S. nakayamae spores varied widely depending on the media formulations used, with glucose yeast peptone consistently yielding the highest D-values for the three temperatures tested. For this same medium, the D-values ranged from 25.24 ± 1.57 to 3.45 ± 0.27 min for the first-order model and from 24.18 ± 0.62 to 3.50 ± 0.24 min for the Weibull model at 70 and 80°C, respectively. The z-values determined for S. nakayamae spores were 11.91 ± 0.29°C for the Weibull model and 11.58 ± 0.43°C for the first-order model. The calculated activation energy was 200.5 ± 7.3 kJ/mol for the first-order model and 192.8 ± 22.1 kJ/mol for the Weibull model. The Weibull model consistently produced the best fit for all the survival curves. This study provides novel and precise information on thermal inactivation kinetics of S. nakayamae spores that will enable reliable thermal process calculations for eliminating this spoilage bacterium.

Optimization of a sample processing protocol for recovery of Bacillus anthracis spores from soil

Following a release of Bacillus anthracis spores into the environment, there is a potential for lasting environmental contamination in soils. There is a need for detection protocols for B. anthracis in environmental matrices. However, identification of B. anthracis within a soil is a difficult task. Processing soil samples helps to remove debris, chemical components, and biological impurities that can interfere with microbiological detection. This study aimed to optimize a previously used indirect processing protocol, which included a series of washing and centrifugation steps. Optimization of the protocol included: identifying an ideal extraction diluent, variation in the number of wash steps, variation in the initial centrifugation speed, sonication and shaking mechanisms. The optimized protocol was demonstrated at two laboratories in order to evaluate the recovery of spores from loamy and sandy soils. The new protocol demonstrated an improved limit of detection for loamy and sandy soils over the non-optimized protocol with an approximate matrix limit of detection at 14spores/g of soil. There were no significant differences overall between the two laboratories for either soil type, suggesting that the processing protocol will be robust enough to use at multiple laboratories while achieving comparable recoveries.

Inactivation of Bacillus anthracis Spores during Laboratory-Scale Composting of Feedlot Cattle Manure

Anthrax outbreaks in livestock have social, economic and health implications, altering farmer’s livelihoods, impacting trade and posing a zoonotic risk. Our study investigated the survival of Bacillus thuringiensis and B. anthracis spores sporulated at 15, 20, or 37°C, over 33 days of composting. Spores (∼7.5 log₁₀ CFU g^-1) were mixed with manure and composted in laboratory scale composters. After 15 days, the compost was mixed and returned to the composter for a second cycle. Temperatures peaked at 71°C on day 2 and remained ≥55°C for an average of 7 days in the first cycle, but did not exceed 55°C in the second. For B. thuringiensis, spores generated at 15 and 21°C exhibited reduced (P < 0.05) viability of 2.7 and 2.6 log₁₀ CFU g^-1 respectively, as compared to a 0.6 log₁₀ CFU g^-1 reduction for those generated at 37°C. For B. anthracis, sporulation temperature did not impact spore survival as there was a 2.5, 2.2, and 2.8 log₁₀ CFU g^-1 reduction after composting for spores generated at 15, 21, and 37°C, respectively. For both species, spore viability declined more rapidly (P < 0.05) in the first as compared to the second composting cycle. Our findings suggest that the duration of thermophilic exposure (≥55°C) is the main factor influencing survival of B. anthracis spores in compost. As sporulation temperature did not influence survival of B. anthracis, composting may lower the viability of spores associated with carcasses infected with B. anthracis over a range of sporulation temperatures.

Incidence, diversity and characteristics of spores of psychrotolerant spore formers in various REPFEDS produced in Belgium

The major objectives of this study were to determine the incidence of psychrotolerant spore formers from REPFEDS marketed in Belgium, and their diversity and characteristics. Spore formers in general were found as spores on 38.3% of the food samples and in 85% food products types evaluated. 76% of the food samples containing spore formers had spores before enrichment. A total of 86 spore formers were isolated from the samples. 28 of 86 bacterial spore formers (32.6%) were capable of vegetative growth at 7 °C. 96% (27/28) of these psychrotolerant spore formers were determined to belong to Bacillus or related genera. According to a (GTG)5-PCR analysis, 24 of these 28 isolates were genetically distinct from each other. 10.7% (3/28) of the bacilli were determined to belong to the Bacillus cereus group, namely B. cereus (chicken curry and Edam cheese) and Bacillus mycoides (Emmental cheese). Almost half of the bacilli (12/27) were putatively identified as Bacillus pumilus, which occurs ubiquitously in nature and has been associated with outbreaks of foodborne disease. Only one psychrotolerant clostridium, Clostridium tyrobutyricum, was isolated in the study. The results of this study show the highly diverse ecology and spoilage potential of psychrotolerant spore formers in REPFEDs marketed in Belgium.

The combined effect of pasteurization intensity, water activity, pH and incubation temperature on the survival and outgrowth of spores of Bacillus cereus and Bacillus pumilus in artificial media and food products

The objective of the study was to evaluate the combined effects of pasteurization intensity (no heat treatment and 10 min at 70, 80 and 90 °C), water activity (aw) (0.960-0.990), pH (5.5-7.0) and storage temperature (7 and 10 °C) on the survival and outgrowth of psychrotolerant spores of Bacillus cereus FF119b and Bacillus pumilus FF128a. The experiments were performed in both artificial media and a validation was performed on real food products (cream, béchamel sauce and mixed vegetable soup). It was determined that in general, heat treatments of 10 min at 70 °C or 80 °C activated the spores of both B. cereus FF119b and B. pumilus FF128a, resulting in faster outgrowth compared to native (non-heat treated) spores. A pasteurization treatment of 10 min at 90 °C generally resulted in the longest lag periods before outgrowth of both isolates. Some of the spores were inactivated by this heat treatment, with more inactivation being observed the lower the pH value of the heating medium. Despite this, it was also observed that under some conditions the remaining (surviving) spores were actually activated as their outgrowth took place after a shorter period of time compared to native non-heated spores. While the response of B. cereus FF119b to the pasteurization intensity in cream and béchamel sauce was similar to the trends observed in the artificial media at 10 °C, in difference, outgrowth was only observed at 7 °C in both products when the spores had been heated for 10 min at 80 °C. Moreover, no inactivation was observed in cream or béchamel sauce when the spores were heated for 10 min at 90 °C in these two products. This was attributed to the protective effect of fat in the cream and the ingredients in the béchamel sauce. The study provides some insight into the potential microbial (stability and safety) consequences of the current trend towards milder heat treatments which is being pursued in the food industry.

Inactivation of Salmonella enterica by UV-C light alone and in combination with mild temperatures

The aim of this investigation was to study the efficacy of the combined processes of UV light and mild temperatures for the inactivation of Salmonella enterica subsp. enterica and to explore the mechanism of inactivation. The doses to inactivate the 99.99% (4D) of the initial population ranged from 18.03 (Salmonella enterica serovar Typhimurium STCC 878) to 12.75 J ml(-1) (Salmonella enterica serovar Enteritidis ATCC 13076). The pH and water activity of the treatment medium did not change the UV tolerance, but it decreased exponentially by increasing the absorption coefficient. An inactivating synergistic effect was observed by applying simultaneous UV light and heat treatment (UV-H). A less synergistic effect was observed by applying UV light first and heat subsequently. UV did not damage cell envelopes, but the number of injured cells was higher after a UV-H treatment than after heating. The synergistic effect observed by combining simultaneous UV and heat treatment opens the possibility to design combined treatments for pasteurization of liquid food with high UV absorptivity, such as fruit juices.

Validated empirical models describing the combined effect of water activity and pH on the heat resistance of spores of a psychrotolerant Bacillus cereus strain in broth and béchamel sauce

The major objective of this study was to evaluate and model the combined effect of the water activity (a(w)) and pH of the heating menstrum on the heat resistance of spores of a psychrotolerant Bacillus cereus strain isolated from béchamel sauce. Two models, a quadratic polynomial equation and a reparameterized function, were assessed for their ability to describe the combined influence of a(w) and pH on the D(85°C)-values of the B. cereus isolate in tryptone soy broth. The performance of the models was validated by challenging the models with data independently collected in broth and béchamel sauce. Both models were found to adequately describe the validation data obtained in broth. However, it was determined that in béchamel sauce the predictions of the polynomial function not only showed bias (bias factor = 1.156) but were also fail-dangerous, as they deviated from the validation data by 17.2%. The reparameterized function was determined to be a good predictor of the D(85°C)-values in béchamel sauce as it showed no bias (bias factor = 1.033) and its predictions differed by only 7.9% from the validation data. The reparameterized function can be used to provide estimates of the minimum processing conditions required to achieve desired levels of spore inactivation within the a(w) and pH ranges studied and to determine the potential changes in heat resistance of B. cereus spores when a(w) and pH are changed, for example, during product reformulation. As validation of heat resistance models is rarely performed, let alone in actual food products, the models evaluated and validated in this study (in particular the reparameterized function) are of immediate relevance to the food industry.

Narrow antagonistic activity of antimicrobial peptide from Bacillus subtilis SCK-2 against Bacillus cereus

Bacillus subtilis SCK-2, producing an antimicrobial peptide of this study, was isolated from Kyeopjang, the Korean traditional fermented-soybean paste. This strain showed a narrow antagonistic activity as it inhibited Bacillus cereus causing food poisoning in human. The antimicrobial peptide, tentatively named AMP IC-1, was purified, characterized, and compared to BSAP-254, another peptide which was previously recovered from traditionally fermented-soybean paste. AMP IC-1 was found to be more thermally stable than BSAP-254, retained inhibitory activity similar to that of BSAP-254 over wide range of pH values, and was also destroyed by proteolytic enzymes. Two compounds were detected by anti-BSAP-254 polyclonal antibody and showed to contain peptide moieties and aliphatic hydrocarbons by Fourier transform infrared analysis. AMP IC-1 had an identical R(f) value (0.69) on TLC plate and a molecular weight similar to that of BSAP-254 (AMP IC-1, m/z 3401; BSAP-254, m/z 3400 to 3473). AMP IC-1 was found to contain about 33 residues and 13 types of amino acids: Cys, Asp or Asn, Glu or Gln, Ser, Gly, Arg, Thr, Ala, Pro, Val, Ile, Leu, and Lys. Compared to BSAP-254, the molar ratios of Asp or Asn, Ser, Val, and Leu were different and only AMP IC-1 contained Arg, but not Trp. Both compounds showed non-hemolytic activity. A partial synergistic effect against B. cereus was observed in response to treatment when AMP IC-1 and BSAP-254 were administered in combination. Therefore, AMP IC-1 is a possible candidate as an antimicrobial agent to prevent food-borne infectious disease in human caused by B. cereus.

Isolation and characterization of a novel analyte from Bacillus subtilis SC-8 antagonistic to Bacillus cereus

In this study, an effective substance was isolated from Bacillus subtilis SC-8, which was obtained from traditionally fermented soybean paste, cheonggukjang. The substance was purified by HPLC, and its properties were analyzed. It had an adequate antagonistic effect on Bacilluscereus, and its spectrum of activity was narrow. When tested on several gram-negative and gram-positive foodborne pathogenic bacteria such as Salmonella enterica, Salmonella enteritidis, Staphylococcus aureus, and Listeria monocytogenes, no antagonistic effect was observed. Applying the derivative from B. subtilis SC-8 within the same genus did not inhibit the growth of major soybean-fermenting bacteria such as Bacillus subtilis, Bacillus licheniformis, and Bacillus amyloquefaciens. The range of pH stability of the purified antagonistic substance was wide (from 4.0 to >10.0), and the substance was thermally stable up to 60 degrees C. In the various enzyme treatments, the antagonistic activity of the purified substance was reduced with proteinase K, protease, and lipase; its activity was partially destroyed with esterase. Spores of B. cereus did not grow at all in the presence of 5mug/mL of the purified antagonistic substance. The isolated antagonistic substance was thought to be an antibiotic-like lipopeptidal compound and was tentatively named BSAP-254 because it absorbed to UV radiation at 254nm.

Modelling the influence of palmitic, palmitoleic, stearic and oleic acids on apparent heat resistance of spores of Bacillus cereus NTCC 11145 and Clostridium sporogenes Pasteur 79.3

Heat resistance of spores is affected by many factors such as temperature, pH, water activity (aw) and others. Previous studies have reported that free fatty acids can affect the germination and growth of bacterial spores. In this study, we investigated the influence of free fatty acids in heating medium or in recovery medium on the heat resistance of spores of Bacillus cereus NTCC 11145 and Clostridium sporogenes Pasteur 79.3. Four free fatty acids were studied: palmitic, palmitoleic, stearic and oleic acids. During thermal treatments, the impact of these FFA in heating media was generally low, but the presence of free fatty acids in the recovery medium highly decreases bacterial spore apparent heat resistance, particularly with unsaturated fatty acids. A mathematical model was developed to describe and quantify the influence of free fatty acids in recovery media on the D-values. The z'(FFA) parameter values which quantify the impact of free fatty acids were determined. The variation of this parameter value according to the free fatty acid type was compared with MIC value variation given in the literature. The model enables the decrease in D-values in the presence of free fatty acids to be estimated. The high concentrations of free fatty acids in liver or canned duck may explain the microbial stability with low sterilization values applied.

The influence of headspace and dissolved oxygen level on growth and haemolytic BL enterotoxin production of a psychrotolerant Bacillus weihenstephanensis isolate on potato based ready-to-eat food products

The major objective of this study was to determine the influence of the initial headspace and dissolved O(2) level and vacuum packaging on growth and diarrhoeal enterotoxin production by Bacillus weihenstephanensis on potato based ready-to-eat food products. In general, the lower the initial headspace or dissolved O(2) level the slower the maximum growth rate (μ(max), log(10) CFU g(-1) d(-1)), the longer the lag phase duration (λ, d) and the smaller the maximum population density (N(max), log(10) CFU g(-1)) became. The slowest μ(max), the longest λ and the smallest N(max) were generally found for growth under vacuum packaging. This implies shorter shelf-lives will occur at higher initial headspace or dissolved O(2) levels as the growth of B. weihenstephanensis to the infective dose of 10(5) CFU g(-1) in such atmospheres takes a shorter time. Significant consumption of dissolved O(2) only occurred when growth shifted from the lag to the exponential phase and growth generally transitioned from the exponential to the stationary phase when the dissolved O(2) levels fell below ca. 75 ppb. Diarrhoeal enterotoxin production (determined via detection of the L2 component of haemolytic BL) was similar for growth under initial headspace O(2) levels of 1-20.9%, and was only reduced when growth took place under vacuum packaging. The reduction in L2 production when growth took place under vacuum was most probably related to the low final cell densities observed under this condition. Both growth and L2 production were inhibited over a 32-day incubation period at 7 °C by 40% CO(2) irrespective of the headspace or dissolved O(2) levels. The results illustrate the importance of residual O(2) and CO(2) on the shelf-stability and safety of modified atmosphere packaged potato based ready-to-eat food products with regards to B. weihenstephanensis.

Evaluation of surface sampling techniques for collection of Bacillus spores on common drinking water pipe materials

Drinking water utilities may face biological contamination of the distribution system from a natural incident or deliberate contamination. Determining the extent of contamination or the efficacy of decontamination is a challenge, because it may require sampling of the wetted surfaces of distribution infrastructure. This study evaluated two sampling techniques that utilities might use to sample exhumed pipe sections. Polyvinyl chloride (PVC), cement-lined ductile iron, and ductile iron pipe coupons (3 cm x 14 cm) cut from new water main piping were conditioned for three months in dechlorinated Cincinnati, Ohio tap water. Coupons were spiked with Bacillus atrophaeus subsp. globigii, a surrogate for Bacillus anthracis. Brushing and scraping were used to recover the inoculated spores from the coupons. Mean recoveries for all materials ranged from 37 +/- 30% to 43 +/- 20% for brushing vs. 24 +/- 10% to 51 +/- 29% for scraping. On cement-lined pipe, brushing yielded a significantly different recovery than scraping. No differences were seen between brushing and scraping the PVC and iron pipe coupons. Mean brushing and scraping recoveries from PVC coupons were more variable than mean recoveries from cement-lined and iron coupons. Spore retention differed between pipe materials and the presence of established biofilms also had an impact. Conditioned PVC coupons (with established biofilms) had significantly lower spore retention (31 +/- 11%) than conditioned cement-lined coupons (61 +/- 14%) and conditioned iron coupons (71 +/- 8%).

Comparison of viability and heat resistance of Clostridium sporogenes stored at different temperatures

The objective of this study was to determine the influence of storage temperature on the viability and heat resistance of Clostridium sporogenes spores. Spore suspension containing both spores and vegetative cells was divided into 3 groups to be stored at different temperatures of -20 (freezing), 4 (refrigerating), and 25 degrees C (ambient temperature). Samples stored for different times within the 2 mo were tested for viability by comparison of colony counts on plates and for heat resistance by determining D values at 121 degrees C. No significant differences were found in the viability of vegetative cells during the storage period, regardless of storage temperatures tested, while the viability of the spores stored for more than 4 wk was significantly higher at 4 degrees C than at -20 degrees C. The heat resistance of spores stored at 4 degrees C for more than 4 wk was remarkably higher than that at 25 degrees C, but similar to that at -20 degrees C throughout the storage period. Consequently, it turned out that a refrigerating temperature of 4 degrees C is satisfactory for storage of C. sporogenes spores in maintaining viability and heat resistance. This study suggests that storage temperature influences the viability and heat resistance of C. sporogenes spores.