Modelling growth of Bacillus cereus in paneer by one-step parameter estimation.

Bacillus cereus phylogenetic group III and IV strains are commonly associated with food products and cause toxin mediated foodborne diseases. These pathogenic strains have been identified from milk and dairy products, such as reconstituted infant formula and several cheeses. Paneer is a fresh, soft cheese originating from India that is prone to foodborne pathogen contamination, such as by Bacillus cereus. However, there are no reported studies of B. cereus toxin formation in paneer or predictive models quantifying growth of the pathogen in paneer under different environmental conditions. This study assessed enterotoxin-producing potential of B. cereus group III and IV strains, isolated from dairy farm environments, in fresh paneer. Growth of a four-strain cocktail of toxin-producing B. cereus strains was measured in freshly prepared paneer incubated at 5-55 °C and modelled using a one-step parameter estimation combined with bootstrap re-sampling to generate confidence intervals for model parameters. The pathogen grew in paneer between 10 and 50 °C and the developed model fit the observed data well (R2 = 0.972, RMSE = 0.321 log10 CFU/g). The cardinal parameters for B. cereus growth in paneer along with the 95% confidence intervals were: µopt 0.812 log10 CFU/g/h (0.742, 0.917); Topt is 44.177 °C (43.16, 45.49); Tmin is 4.405 °C (3.973, 4.829); Tmax is 50.676 °C (50.367, 51.144). The model developed can be used in food safety management plans and risk assessments to improve safety of paneer while also adding to limited information on B. cereus growth kinetics in dairy products.

Pathogen growth when implementing 'Time as a Public Health Control'.

Food regulatory authorities permit the use of Time as Public Health Control (TPHC) for handling foods that potentially support the growth of pathogenic bacteria. Considering the widespread use of TPHC in food service operations, few reports quantitatively describe potential pathogen growth when these protocols are implemented. A worst-case growth rate model was built from the highest growth rates predicted by ComBase broth-based models for six pathogens. A separate worst-case growth model was constructed from growth rates in ComBase database records. The maximum estimated pathogen growth in 4 h, assuming no lag phase, ranged from 0.006 log CFU at 5 °C to 6.16 log CFU at 44 °C, with 3.1 log CFU at 25 °C. In addition, pathogen growth when implementing TPHC could exceed the 1- and 3-log limits recommended for food challenge tests. The use of predictive models in development of TPHC criteria may provide more fail-safe strategies for managing microbial hazards in potentially hazardous food. This strategy could also reduce food waste and promote the use of temperature sensors in food supply chains.

Modelling viability of Listeria monocytogenes in paneer.

Paneer is a fresh, soft ready-to-eat cheese that is susceptible to Listeria monocytogenes contamination, exemplified by product recalls in Australia, Canada, and the USA. Previous research demonstrates that L. monocytogenes grows in paneer, however there are no paneer-specific predictive models that quantify the effect of environmental conditions on L. monocytogenes viability. This study measured the viability of a five-strain cocktail of L. monocytogenes in freshly prepared paneer incubated at 4-40 °C. Growth rates were fitted with the extended Ratkowsky square root model, with growth rates ranging from 0.014 to 0.352 log10 CFU/h. In comparison with published models, only the ComBase L. monocytogenes broth model acceptably predicted growth (Bf = 1.01, Af = 1.12) versus the developed model. The influence of paneer pH (5.0-6.0) and storage temperature (41-45 °C) on L. monocytogenes growth at the upper temperature growth boundary was described using a logistic model. These models provide quantitative tools to improve the safety of paneer processing conditions, shelf-life estimation, food safety management plans, and risk assessment.

Effect of glucose, pH and lactic acid on Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens within a commercial heat-shrunk vacuum-package film.

Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens are common spoilage organisms found within the microbiome of refrigerated vacuum-packaged (VP) beef. Extending and predicting VP beef shelf-life requires knowledge about how spoilage bacteria growth is influenced by environmental extrinsic and intrinsic factors. Multifactorial effects of pH, lactic acid (LA) and glucose on growth kinetics were quantified for C. maltaromaticum, B. thermosphacta and S. liquefaciens within a heat shrink-wrapped VP commercial film containing a simulated beef medium. LA, pH, and undissociated lactic acid (UDLA) significantly affected bacterial growth rate (p < 0.001), whereas 5.55 mM glucose produced a marginal effect. At 1.12 mM UDLA, growth rate and maximum population density decreased 20.9 and 3.5%, 56 and 7%, and 11 and 2% for C. maltaromaticum, B. thermosphacta, and S. liquefaciens, respectively.

Salmonella enterica in Mexico 2000-2017: Epidemiology, Antimicrobial Resistance, and Prevalence in Food.

In Mexico, information of Salmonella enterica cases linked to food consumption is scarce. The objective of this article was to assess how S. enterica affect public health in Mexico. To conduct this study, data on the epidemiology of nontyphoidal S. enterica (NTS), Salmonella Typhi, and Salmonella Paratyphi A collected from 2000 to 2017 through the National Epidemiological Surveillance System of Mexico (Sistema Nacional de Vigilancia Epidemiológica de Mexico [SINAVE]) were used. Geographical distribution, season, age groups, and gender were variables considered to analyze S. enterica incidence. An estimation of cases caused by S. enterica in Mexico was calculated while considering data underestimation and the proportion of foodborne diseases. Information of the prevalence of the pathogen in food and the antimicrobial resistance of isolates from food and human cases were obtained from published studies. Outbreaks of S. enterica derived from imported Mexican products in the Unites States are discussed. In 2017, the numbers of reported cases of NTS (92,013) were two and seven times higher than the reported cases of Salmonella Typhi (45,280) and Salmonella Paratyphi A (12, 458). The NTS incidence was higher in lower socioeconomic Mexican regions. The gaps in the surveillance system make it impossible to establish a reliable tendency among age groups, geographical distribution, and gender. In 2017, the estimated frequency of NTS foodborne cases was 49 times higher than that reported in SINAVE, whereas for Salmonella Typhi and Salmonella Paratyphi A it was 23 times. Fresh meat showed the highest prevalence of S. enterica, and most of their isolates had multidrug resistance. Salmonella Typhimurium was the most common serotype isolated from human cases and food. Food safety agencies in Mexico need to prioritize efforts and resources to establish guidelines to ensure the absence of S. enterica in food.

Integrating predictive models and sensors to manage food stability in supply chains.

Food products move through complex supply chains, which require effective logistics to ensure food safety and to maximize shelf-life. Predictive models offer an efficient means to monitor and manage the safety and quality of perishable foods, however models require environmental data to estimate changes in microbial growth and sensory attributes. Currently, several companies produce Time-Temperature Indicators that react at rates that closely approximate predictive models; these devices are simple and cost-effective for food companies. However, even greater outcomes could be realized using sensors that transfer data to predictive models in real-time. This report describes developments in predictive models designed for supply chain management, as well as advances in environmental sensors. Important innovation can be realized in both supply chain logistics and food safety management by integrating these technologies.

Atlantic Salmon (Salmo salar L.) Gastrointestinal Microbial Community Dynamics in Relation to Digesta Properties and Diet.

To better understand salmon GI tract microbial community dynamics in relation to diet, a feeding trial was performed utilising diets with different proportions of fish meal, protein, lipid and energy levels. Salmon gut dysfunction has been associated with the occurrence of casts, or an empty hind gut. A categorical scoring system describing expressed digesta consistency was evaluated in relation to GI tract community structure. Faster growing fish generally had lower faecal scores while the diet cohorts showed minor differences in faecal score though the overall lowest scores were observed with a low protein, low energy diet. The GI tract bacterial communities were highly dynamic over time with the low protein, low energy diet associated with the most divergent community structure. This included transiently increased abundance of anaerobic (Bacteroidia and Clostridia) during January and February, and facultatively anaerobic (lactic acid bacteria) taxa from February onwards. The digesta had enriched populations of these groups in relation to faecal cast samples. The majority of samples (60-86 %) across all diet cohorts were eventually dominated by the genus Aliivibrio. The results suggest that an interaction between time of sampling and diet is most strongly related to community structure. Digesta categorization revealed microbes involved with metabolism of diet components change progressively over time and could be a useful system to assess feeding responses.

Microbial and sensorial models for head-on and gutted (HOG) Atlantic Salmon (Salmo salar) stored from 0 to 15 °C.

Predictive models offer efficient means to manage the quality and safety of highly perishable seafood. Salmon is an increasingly popular seafood, and relies on well managed domestic and international supply chains to minimize growth of spoilage and pathogenic bacteria. While the literature describes predictive models for smoked and modified atmosphere packaged salmon, there are no reported models for spoilage bacteria and Listeria monocytogenes on head-on and gutted (HOG) aerobically-stored Atlantic salmon. Predictive models were developed for microbial and sensorial degradation of HOG Atlantic salmon stored at 0-15 °C until the end of shelf-life. Total Viable Count (TVC) and Pseudomonas spp. had similar growth rates at 0, 5 and 10 °C, but TVC rate was higher at 15 °C. L. monocytogenes growth rate at 0 °C was 0.004 log10 cfu/h, and showed a log-linear increase (R(2) = 0.99) to 0.079 log10 cfu/h at 15 °C. Sensory Quality Index (QI) scores were 2.4, 4.5, and 7.2 times greater at 5, 10 and 15 °C, respectively, compared to 0 °C. QI and TVC rates had a relatively strong relationship at 5 (R(2) = 0.87), 10 (R(2) = 0.80) and 15 °C (R(2) = 0.78), compared to 0 °C (R(2) = 0.50). These models are potential tools to manage the safety and quality of HOG Atlantic salmon in supply chains.

High-throughput sequencing of microbial communities in Poro cheese, an artisanal Mexican cheese.

The bacterial diversity and structure of Poro cheese, an artisanal food, was analysed by high-throughput sequencing (454 pyrosequencing) in order to gain insight about changes in bacterial communities associated with the cheese-making process. Dairy samples consisting of milk, fermented whey, curd and ripened cheese (during 7 and 60 d) were collected from three manufacturers located in the state of Tabasco, México during dry (March-June) and rainy (August-November) seasons. Independently of producer and season, raw milk samples displayed the highest diversity in bacterial communities. In raw milk, genera found were Macrococcus, Staphylococcus, Enterococcus, Streptococcus, Lactobacillus and Enhydrobacter. Diversity in whey, curd and cheese was lower, principally containing Streptococcus and Lactobacillus; however, bacteria such as Staphylococcus, Acinetobacter, Chryseobacterium, Bacillus, Sediminibacter, Lactococcus and Enterococcus were occasionally present. After curdling step, the most dominant and abundant species were Streptococcus thermophilus and Lactobacillus delbrueckii.

Development and validation of a predictive model for the growth of Vibrio vulnificus in postharvest shellstock oysters.

Postharvest growth of Vibrio vulnificus in oysters can increase risk of human infection. Unfortunately, limited information is available regarding V. vulnificus growth and survival patterns over a wide range of storage temperatures in oysters harvested from different estuaries and in different oyster species. In this study, we developed a predictive model for V. vulnificus growth in Eastern oysters (Crassostrea virginica) harvested from Chesapeake Bay, MD, over a temperature range of 5 to 30°C and then validated the model against V. vulnificus growth rates (GRs) in Eastern and Asian oysters (Crassostrea ariakensis) harvested from Mobile Bay, AL, and Chesapeake Bay, VA, respectively. In the model development studies, V. vulnificus was slowly inactivated at 5 and 10°C with average GRs of -0.0045 and -0.0043 log most probable number (MPN)/h, respectively. Estimated average growth rates at 15, 20, 25, and 30°C were 0.022, 0.042, 0.087, and 0.093 log MPN/h, respectively. With respect to Eastern oysters, bias (B(f)) and accuracy (A(f)) factors for model-dependent and -independent data were 1.02 and 1.25 and 1.67 and 1.98, respectively. For Asian oysters, B(f) and A(f) were 0.29 and 3.40. Residual variations in growth rate about the fitted model were not explained by season, region, water temperature, or salinity at harvest. Growth rate estimates for Chesapeake Bay and Mobile Bay oysters stored at 25 and 30°C showed relatively high variability and were lower than Food and Agricultural Organization (FAO)/WHO V. vulnificus quantitative risk assessment model predictions. The model provides an improved tool for designing and implementing food safety plans that minimize the risk associated with V. vulnificus in oysters.

Prevalence, characterization and sources of Listeria monocytogenes in blue crab (Callinectus sapidus) meat and blue crab processing plants.

Seven blue crab processing plants were sampled to determine the prevalence and sources of Listeria spp. and Listeria monocytogenes for two years (2006-2007). A total of 488 raw crabs, 624 cooked crab meat (crab meat) and 624 environmental samples were tested by standard methods. Presumptive Listeria spp. were isolated from 19.5% of raw crabs, 10.8% of crab meat, and 69.5% of environmental samples. L. monocytogenes was isolated from 4.5% of raw crabs, 0.2% of crab meat, and 2.1% of environmental samples. Ninety-seven percent of the isolates were resistant to at least one of the ten antibiotics tested. Eight different serotypes were found among 76 L. monocytogenes isolates tested with the most common being 4b, 1/2b and 1/2a. Automated EcoRI ribotyping differentiated 11 ribotypes among the 106 L. monocytogenes isolates. Based on ribotyping analysis, the distribution of the ribotypes in each processing plant had a unique contamination pattern. A total of 92 ApaI and 88 AscI pulsotypes among the 106 L. monocytogenes isolates were found and distinct pulsotypes were observed in raw crab, crab meat and environmental samples. Ribotypes and serotypes recovered from crab processing plants included subtypes that have been associated with listeriosis cases in other food outbreaks. Our findings suggest that molecular methods may provide critical information about sources of L. monocytogenes in crab processing plants and will augment efforts to improve food safety control strategies such as targeting specific sources of contamination and use of aggressive detergents prior to sanitizing.

Quantitative modeling of the survival of Listeria monocytogenes in soy sauce-based acidified food products.

Primary and secondary models were developed for quantitatively characterizing the survival of Listeria monocytogenes in soy-sauce based acidified Asian style products that do not undergo a thermal treatment. The objective of this study was to quantify the effect of food matrix properties on L. monocytogenes' survival in soy sauce-based products. This quantification enables a product-specific estimation of 5-log reduction time to ensure a safe processing and management operation, to ultimately facilitate a science-based, safety-oriented product development process. A central composite design with four independent variables (pH, soy sauce, added NaCl and soluble solids) with five levels was used to plan the challenge studies on different formulations. To model microbial survival over time, different non-linear primary models were fit to the data obtained from challenge studies. The best-fit model was selected based on a series of statistical goodness-of-fit measures. Kinetic parameters estimated from the best-fit primary models were fit to response surface equations using second order polynomial regression. The best-fit primary model representative of the product formulations was a modified Weibull model. The natural logarithm of the scale parameter (δ, in h) was used as the response variable for the secondary model. This resulted in acceptable fitting compared to the observed values with R2 values of 0.95 and RMSE of 0.7 h. External validity of model predictions was conducted by comparing them to 5-log reduction times observed in independent challenge tests using different product formulations. Results indicated an acceptable validation with R2 = 0.81 and RMSE = 35 h. The present study provides quantitative tools specific for cold-fill-hold soy sauce-based products to enhance microbial safety management plans and product development.

Modelling growth and histamine formation of Klebsiella aerogenes TI24 isolated from Indonesian pindang.

Indonesian salted-boiled fish (pindang) is a popular traditional food in Indonesia, which is made from Scombroid fish such as tuna and mackerel. As with other traditionally prepared fish products, pindang has important economic and social values, especially for those living in the coastal areas of Indonesia. However, pindang is a major cause of histamine fish poisoning (HFP) for consumers. Klebsiella aerogenes T124, a relatively high histamine-producing isolate from pindang, was used to describe lag time (λ), growth rate (µmax), maximum population density (Nmax), and histamine production in histidine broth and artificially contaminated Grey mackerel. Broth was adjusted to 1.5, 6, 10 and 20% w/v NaCl; mackerel was treated with 6% w/w NaCl, a level common to Indonesian industry practice, or not treated with additional NaCl. Samples were incubated at 10, 15, 20 and 30 °C. In broth, µmax and Nmax were significantly affected by temperature and NaCl, respectively, with λ influenced by both parameters. In control fish, µmax was significantly affected by temperature and NaCl, except at 10 and 15 °C; for 6% NaCl treatment, growth was only observed at 20 and 30 °C. Under similar incubation conditions for broth and fish, histamine formation was markedly affected by NaCl concentration. In broth, -5.1 to -6.6 log µg of histamine was produced per CFU, versus -4.6 to -6.6 log µg per CFU in fish. This study demonstrated that mackerel treated with 6% NaCl and stored at 10-15 °C prevents growth of K. aerogenes strain TI24 and formation of toxic levels of histamine.

Detection, quantification, and characterization of Salmonella enterica in mango, tomato, and raw chicken purchased in the central region of Mexico.

To estimate human exposure to Salmonella enterica, it is essential to understand the pathogen distribution and characteristics. Prevalence and concentration of S. enterica were determined in mango, tomato, and raw chicken samples purchased in three states (Aguascalientes, Querétaro, and Guadalajara) located in the central region of Mexico during two seasons. In addition, S. enterica isolates were characterized by absence/presence of 13 virulence genes (chromosomal, prophage, and plasmid) and resistance to 14 antibiotics. A total of 300 samples of mango, 272 of tomato, and 354 of raw chicken were analyzed. The mean of the prevalence (24.9%) and concentration (-0.61 Log MPN/g) of S. enterica in chicken was higher than in mango (1.3%, -1.7 Log MPN/g) and tomato (1.1%, -1.7 Log MPN). Among S. enterica isolates (284), there were 7 different virulotypes, belonging 68.7% of isolates to V2; there was high variability in the presence of mobile genetic elements. The occurrence of specific mobile elements ranged from 81.4% to 11.3% among isolates. Among the isolates, 91.5% were resistant to at least one antibiotic with ampicillin being the most frequent; 54.9% of isolates were multidrug resistant. Data from this study can be used for quantitative microbial risk assessment of S. enterica related to mango, tomato, and raw chicken consumption in the central region of Mexico. PRACTICAL APPLICATION: Data on the prevalence and concentration of Salmonella enterica obtained in this study can be used to estimate the exposure assessment for the consumption of mango, tomato, and chicken in the central region of Mexico. In addition, the characteristics of the S. enterica isolates could be used to select representative strains for future studies to evaluate the intraspecies variability.

Predictive models for the effect of storage temperature on Vibrio parahaemolyticus viability and counts of total viable bacteria in Pacific oysters (Crassostrea gigas).

Vibrio parahaemolyticus is an indigenous bacterium of marine environments. It accumulates in oysters and may reach levels that cause human illness when postharvest temperatures are not properly controlled and oysters are consumed raw or undercooked. Predictive models were produced by injecting Pacific oysters (Crassostrea gigas) with a cocktail of V. parahaemolyticus strains, measuring viability rates at storage temperatures from 3.6 to 30.4°C, and fitting the data to a model to obtain parameter estimates. The models were evaluated with Pacific and Sydney Rock oysters (Saccostrea glomerata) containing natural populations of V. parahaemolyticus. V. parahaemolyticus viability was measured by direct plating samples on thiosulfate-citrate-bile salts-sucrose (TCBS) agar for injected oysters and by most probable number (MPN)-PCR for oysters containing natural populations. In parallel, total viable bacterial counts (TVC) were measured by direct plating on marine agar. Growth/inactivation rates for V. parahaemolyticus were -0.006, -0.004, -0.005, -0.003, 0.030, 0.075, 0.095, and 0.282 log10 CFU/h at 3.6, 6.2, 9.6, 12.6, 18.4, 20.0, 25.7, and 30.4°C, respectively. The growth rates for TVC were 0.015, 0.023, 0.016, 0.048, 0.055, 0.071, 0.133, and 0.135 log10 CFU/h at 3.6, 6.2, 9.3, 14.9, 18.4, 20.0, 25.7, and 30.4°C, respectively. Square root and Arrhenius-type secondary models were generated for V. parahaemolyticus growth and inactivation kinetic data, respectively. A square root model was produced for TVC growth. Evaluation studies showed that predictive growth for V. parahaemolyticus and TVC were "fail safe." The models can assist oyster companies and regulators in implementing management strategies to minimize V. parahaemolyticus risk and enhancing product quality in supply chains.

Lysozyme as a barrier to growth of Bacillus anthracis strain Sterne in liquid egg white, milk and beef.

In this study, we investigated the role of lysozyme on the viability of Bacillus cereus, Bacillus subtilis, Bacillus pumilus and Bacillus anthracis (Sterne) in egg white (EW), ground beef and milk. At 35 °C in EW, growth rates (GR) for B. cereus, B. subtilis, B. pumilus and B. anthracis were 0.005, -0.018, -0.028 and -0.029 OD(600)/h, respectively. Heat-treating EW at 55 and 60 °C reduced the inactivating effect of EW by 3.1 and 10.5-fold, respectively. Addition of lysozyme (2 mg/ml) to 60 °C-treated EW increased the inactivation rate 5.76-fold, indicating involvement of lysozyme in B. anthracis inactivation. B. anthracis inactivation was influenced by pH, as shown by a progressive increase in inactivation rate from 0.25 to -4.42 logs CFU/h over a pH range of 6.0-8.5. Adding 2 mg/ml lysozyme to milk and ground beef also suppressed the growth of B. anthracis 3.3 and 6.5-fold, respectively. These data indicate that lysozyme, as a natural component of EW or potential additive in other foods, could reduce biothreat risks presented by bioterror agents.

Kinetics of growth and inactivation of Salmonella enterica serotype Typhimurium DT104 in pasteurised liquid egg products.

The potential impact of post-pasteurisation contamination of liquid egg products with the multi-antibiotic resistant pathogen Salmonella enterica serotype Typhimurium definitive type 104 (DT104) was assessed by determining the viability of this bacterium in whole egg, albumen and 10% w/w sugared and salted yolk incubated at 4-42 degrees C. Results indicated that populations of S. Typhimurium DT104 were slowly inactivated in all four products when stored at 4 degrees C. However, based on the typical shelf-lives of cold-stored liquid egg, less than 0.6 log-kill would be achieved in those products prior to their use. Incubation at temperatures pertaining to abuse situations (10, 15, 20 and 25 degrees C) revealed an increasing potential for growth of S. Typhimurium DT104 in whole egg, albumen and sugared yolk, as indicated by trends in growth rate, lag duration and maximum population density. At even higher temperatures (30, 37 and 42 degrees C), growth rates of S. Typhimurium DT104 in whole egg and sugared yolk continued to increase. The same was true for S. Typhimurium DT104 in albumen except that growth was not observed at 42 degrees C and instead populations were inactivated within 30 h. At no temperature tested was S. Typhimurium DT104 able to grow in salted yolk. The influence of these growth and inactivation patterns on the risk of salmonellosis in relation to product type and storage temperature is discussed.

qPCR quantification of Carnobacterium maltaromaticum, Brochothrix thermosphacta, and Serratia liquefaciens growth kinetics in mixed culture.

Quantifying growth kinetics of specific spoilage microorganisms in mixed culture is required to describe the evolution of food microbiomes. A qPCR method was developed to selectively amplify individual meat spoilage bacteria, Carnobacterium maltaromaticum, Brochothrix thermosphacta and Serratia liquefaciens, within a broth medium designed to simulate the composition of beef. An optimized method of DNA extraction was produced for standard curve construction. Method specificity was determined by individual single peaks in melt curves. Reaction efficiency for standard curves of C. maltaromaticum, B. thermosphacta and S. liquefaciens was high (R2 = 0.98-0.99), and linear quantification was achieved over a 5 log CFU/ml range. Coefficient of variation was calculated considering both threshold cycle (Ct) and bacterial concentration; the value did not exceed 14% for inter- or intra-runs for either method. Comparison of growth kinetic parameters derived from plate count and qPCR showed no significant variation (P > .05) for growth rate (GR) and maximum population density (MPD); lag phase duration (LPD) was not included in this comparison due to high innate variability. Log quantification of each isolate was validated in a mixed-culture experiment for all three species with qPCR and plate count differing less than 0.3 log CFU/ml (average 0.10 log CFU/ml, R2 = 0.98).

Validation of cooking times and temperatures for thermal inactivation of Yersinia pestis strains KIM5 and CDC-A1122 in irradiated ground beef.

Irradiated ground beef samples (ca. 3-g portions with ca. 25% fat) inoculated with Yersina pestis strain KIM5 (ca. 6.7 log CFU/g) were heated in a circulating water bath stabilized at 48.9, 50, 52.5, 55, 57.5, or 60 degrees C (120, 122, 126.5, 131, 135.5, and 140 degrees F, respectively). Average D-values were 192.17, 34.38, 17.11, 3.87, 1.32, and 0.56 min, respectively, with a corresponding z-value of 4.67 degrees C (8.41 degrees F). In related experiments, irradiated ground beef patties (ca. 95 g per patty with ca. 25% fat) were inoculated with Y. pestis strains KIMS or CDC-A1122 (ca. 6.0 log CFU/g) and cooked on an open-flame gas grill or on a clam-shell type electric grill to internal target temperatures of 48.9, 60, and 71.1 degrees C (120, 140, and 160 degrees F, respectively). For patties cooked on the gas grill, strain KIM5 populations decreased from ca. 6.24 to 4.32, 3.51, and < or = 0.7 log CFU/g at 48.9, 60, and 71.1 degrees C, respectively, and strain CDC-A1122 populations decreased to 3.46 log CFU/g at 48.9 degrees C and to < or = 0.7 log CFU/g at both 60 and 71.1 degrees C. For patties cooked on the clam-shell grill, strain KIM5 populations decreased from ca. 5.96 to 2.53 log CFU/g at 48.9 degrees C and to < or = 0.7 log CFU/g at 60 or 71.1 degrees C, and strain CDC-A1122 populations decreased from ca. 5.98 to < or = 0.7 log CFU/g at all three cooking temperatures. These data confirm that cooking ground beef on an open-flame gas grill or on a clam-shell type electric grill to the temperatures and times recommended by the U.S. Department of Agriculture and the U.S. Food and Drug Administration Food Code, appreciably lessens the likelihood, severity, and/or magnitude of consumer illness if the ground beef were purposefully contaminated even with relatively high levels of Y. pestis.

The survivability of Bacillus anthracis (Sterne strain) in processed liquid eggs.

In this study, we investigated the survival and inactivation kinetics of a surrogate strain of Bacillus anthracis (Sterne strain) in whole egg (WE), egg white (EW), sugared egg yolk (YSU), and salted egg yolk (YSA) at low (-20, 0, and 5 degrees C), moderate (15, 20, 25, 30, 35, and 40 degrees C), and high storage temperatures (45, 50, 55, and 60 degrees C). Outgrowth of the spores was measured as lag phase duration (LPD). Replication of vegetative cells was measured in terms of growth rate (GR) and maximum population density (MPD). Spore inactivation was recorded as inactivation rate and percent reduction in viable count. In general, spore viability decreased at low and high temperatures and increased at moderate temperatures. At 0 and 5 degrees C, a 60-100% reduction in spore viability was seen within 2-3 weeks in WE and YSU, 0-30% in YSA, and 50-100% in EW. At -20 degrees C, however, no drop in spore titer was observed in YSU and EW but a 20% drop in titer was seen in YSA and 50% in WE within 2-3 weeks. At high temperatures, WE, EW, and YSA produced a 20-50% drop in the spore titer within 1-4h whereas YSU showed 100% inactivation within 0.75 h. At moderate storage temperatures, as the temperature increased from 15 to 40 degrees C, LPD decreased from 13.5 to 0.75 h and MPD reached 0.27-2.2 x1 0(9) CFU/ml in YSU and WE, respectively. Markedly lower growth was observed in YSA (LPD=24-270 h, MPD=9 x 10(5) CFU/ml) and spores were inactivated completely within 1-6h in EW. The survivability and inactivation data of B. anthracis in liquid egg products reported in this investigation will be helpful in developing risk assessment models on food biosecurity.