Search

The topic of food safety continues to receive increased attention and has ramifications on various human, environmental, policy, and economic levels worldwide. By garnering feedback from 30 food industry experts, this study was undertaken to identify the most critical issues facing the food industry in relation to food safety. According to expert opinion and after three rounds of Delphi inquiry, food contamination detection, outbreaks, and prevention along with governmental oversight, education for and communication with consumers and employees, and globalization were identified as the main areas at the forefront of food safety. Delphi and constant comparative research methods are explained, and suggestions on how to make meaning from the results to progress in this area are discussed. HIGHLIGHTS

The potential transmission of SARS-CoV-2 via food has been controversial since the beginning of the COVID-19 pandemic. To investigate these concerns, reliable detection methods and data on virus die-off rates in various foods are needed. Here, an FDA-standard method for the detection of enteric viruses' RNA from soft fruits was modified for the recovery of infectious SARS-CoV-2. Then, the survival of SARS-CoV-2 on berries was investigated as well as the effectiveness of washing virus-contaminated berries with water. The modified method did not significantly reduced log infectivity titers of recovered viruses, but berries did. The detection limit of the method for infectious SARS-CoV-2 was ∼2.97 log TCID50/g of berries. On SARS-CoV-2-inoculated berries that were stored at 4 °C for 7 days, significant reductions in SARS-CoV-2 infectivity were observed over time. In contrast, on frozen berries, infectious SARS-CoV-2 was recovered for 28 days without significant reductions. Washing SARS-CoV-2-inoculated berries with water removed90% of infectious viruses within 10 min; however, infectious viruses were detected in wash water. Therefore, on fresh berries infectious viruses are markedly inactivated over time and can be largely removed by washing with water. However, the prolonged survival of SARS-CoV-2 on frozen berries suggests that the virus can potentially spread through frozen fruits.

This project was undertaken to determine the kinetic parameters of thermal inactivation of Listeria monocytogenes on pecans, macadamia nuts, and sunflower seeds subjected to heat treatments simulating industry processes. Five strains were grown in nonselective medium, mixed, and resuspended before inoculating macadamia nuts, pecans, and sunflower seeds (6 to 9 Log CFU/g). Redried inoculated pecans and macadamia nuts were heated in an oven at a temperature range of 90 to 140°C. Unshelled sunflower seeds were heated in sunflower seed oil. The thermal inactivation was determined by measuring viable cell counts using standard microbiological methods. Average count data were fit to the log-linear model, and thermal-death kinetics were calculated. On pecans, the viable Listeria counts were reduced by 3 and 3.5 Log CFU/g after 40 min at 110°C and 8 min at 140°C, respectively. On macadamia nuts, the L. monocytogenes population was reduced by 5 Log CFU/g after 20 min at 120°C. Unshelled sunflower seeds were subjected to heat treatment via a hot-oil bath. On sunflower seeds, >7 Log CFU/g reductions were observed after 15 min at 120°C. The thermal resistance (D value) for inactivation on pecans at 140°C was 3.1 min and on macadamia nuts at 120°C was 4.4 min. The inactivation of L. monocytogenes was influenced by the kind of nut or seed. These results suggest that L. monocytogenes has a relatively high thermal tolerance. The findings from this study will contribute to the assessment of the effectiveness of heat treatment for control of this pathogen on nuts and seeds. IMPORTANCE Listeria monocytogenes is a major concern for the food industry in ready-to-eat (RTE) foods. In recent years, large-scale recalls have occurred with contaminated sunflower seeds and macadamia nuts that triggered product withdrawals. These events stress the importance of understanding Listeria’s ability to survive heat treatments in these low-water activity foods. Nuts and seeds are subjected to a variety of thermal treatments typically referred as roasting. To date, no listeriosis outbreak has been linked to nuts and seeds, but the recent recognition that this pathogen can be detected in commercial products stresses the need for research on thermal treatments. The characterization of heat inactivation kinetics at temperatures typically used during roasting processes will be very beneficial for validation studies. This manuscript reports inactivation rates of L. monocytogenes strains inoculated onto macadamia nuts, sunflower seeds, and pecan halves subjected to temperatures between 90 and 140°C.

Salsa-associated outbreaks, including the large multistate outbreak in the United States in 2008 caused by jalapeño and serrano peppers contaminated with Salmonella Saintpaul, have raised concerns about salsa as a potential vehicle for transmission. Despite these events, there has been relatively limited research on the potential growth of pathogenic bacteria in salsa. The aim of this study was to characterize the survival and growth of Salmonella, including the outbreak strain of Salmonella Saintpaul (E2003001236), in freshly made salsa and its main ingredients. Chopped tomatoes, jalapeño peppers, cilantro, and onions were tested individually or mixed according to different salsa recipes. Samples were inoculated with five Salmonella serotypes at 3 log CFU/g: Saintpaul (various strains), Typhimurium, Montevideo, Newport, or Enteritidis. Samples were then stored at room temperature (23°C) for up to 12 h or 3 days. The Salmonella Saintpaul levels reached approximately 9 log CFU/g after 2 days in tomato, jalapeño pepper, and cilantro. Growth was slower in onions, reaching 6 log CFU/g by day 3. Salsa recipes, with or without lime juice, supported the growth of Salmonella Saintpaul, and final levels were approximately 7 log CFU/g after 3 days at 23°C. In contrast, the counts of Salmonella Typhimurium, Salmonella Montevideo, Salmonella Newport, and Salmonella Enteritidis increased only 2 log CFU/g after 3 days in any of the salsas. Other Salmonella Saintpaul strains were able to grow in salsas containing 10% lime juice, but their final levels were less than 5 log CFU/g. These findings indicate the enhanced ability of the Salmonella Saintpaul outbreak strain to grow in salsa compared with other Salmonella strains. Recipe modifications including but not limited to adding lime juice (at least 10%) and keeping fresh salsa at room temperature for less than 12 h before consumption are strategies that can help mitigate the growth of Salmonella in salsa.

In nature, Listeria may interact competitively and cooperatively with other organisms, resulting in unique spatial organization and functions for cells within the community. This study was undertaken to characterize the biofilm architecture of binary biofilms of Listeria monocytogenes and Lactobacillus species and to assess their effect on the survival of Listeria during exposure to hypochlorite. Three L. monocytogenes strains, ATCC 19115 (Lm5), ATCC 19117 (Lm7), and Coleslaw (LmC), were selected and combined individually with three Lactobacillus strains: L. fermentum (Lf), L. bavaricus (Lb), and L. plantarum (Lp). In binary Lm-Lp biofilms, the Lm cell counts were similar to single-species biofilms (8.5 log CFU/well), and the Lp cell numbers declined by 1.0 log CFU/well. In the presence of Lb, the Lm cell counts were reduced by 1.5 log CFU/well (p < 0.05), whereas the Lf cell counts increased at least by 3.5 log CFU/well. Confocal laser scanning microscopy (CLSM) determined that interspecies interactions significantly affected the spatial organization of three binary biofilms. Biofilm surface-to-volume ratio increased from 0.8 μm2/μm3 for Lm5 in the monoculture to 2.1 μm2/μm3 for Lm5-Lp in the dual-species model (p < 0.05), and was characterized by a thicker structure with a largely increased surface area. Biofilm roughness increased from 0.2 for Lm7 to 1.0 for Lm7-Lb biofilms (p < 0.05), which appeared as interspecific segregation. Biofilm thickness increased from 34.2 μm for LmC to 46.3 μm for LmC–Lf (p < 0.05), which produced flat and compact structures that covered the entire surface available. The biomass of the extracellular matrix was higher in the case of some binary biofilms (p < 0.05); however, this effect was dependent upon the species pair. When treated with hypochlorite, Lm5 in binary biofilms had an approximately 1.5 log CFU/well greater survival than individually. The unique spatial organization and greater protein production may explain the protective effect of Lp after hypochlorite exposure.

Current consumer preferences for both clean label food ingredients and convenience-based foods has provided a unique opportunity to explore the application of novel natural food preservatives in sous vide products. The anaerobic environment and relatively low thermal processing of the sous vide process creates a favorable environment for the survival, germination, and outgrowth of spore-forming bacterium Clostridium perfringens. The aim of this study was to identify effective novel natural ingredient formulations against C. perfringens and apply them within a vacuum-sealed sous vide chicken model exposed to abusive storage and chilling conditions. Among six commercial vinegar-based formulations, liquid vinegar with citrus extract (CE; 1.0%) and with lemon juice concentrate (LJC; 1.5%) were identified as the most effective at inhibiting three individual C. perfringens strains. Both reduced viable cell counts by 5 log CFU/mL (P 0.05), whereas reductions in spore counts ranged from 2 to 4 log CFU/mL depending on formulation and concentration used. Once incorporated to chicken meat 1.0% CE and 1.5% LJC before sous-vide cooking, completely inhibited the growth of mixed C. perfringens strains (P 0.05) during storage for 16 days at 12 and 16 °C. Exponential cooling from 54 to 4 °C was performed for 18 h to imitate abusive storage conditions. CE and LJC at 3.0% inhibited growth and reduced counts by 3.4 and 2.9 log CFU/g compared to respective controls. Treatments CE and LJC could be implemented within the formulation of a sous vide chicken product to provide an effective protection against C. perfringens meeting clean label expectations.

Food safety is a new area for novel applications of metagenomics analysis, which not only can detect and subtype foodborne pathogens in a single workflow but may also produce additional information with in-depth analysis capabilities. In this study, we applied a quasimetagenomic approach by combining short-term enrichment, immunomagnetic separation (IMS), multiple-displacement amplification (MDA), and nanopore sequencing real-time analysis for simultaneous detection of Salmonella and Escherichia coli in wheat flour. Tryptic soy broth was selected for the 12-h enrichment of samples at 42°C. Enrichments were subjected to IMS using beads capable of capturing both Salmonella and E. coli. MDA was performed on harvested beads, and amplified DNA fragments were subjected to DNA library preparation for sequencing. Sequencing was performed on a portable device with real-time basecalling adaptability, and resulting sequences were subjected to two parallel pipelines for further analysis. After 1 h of sequencing, the quasimetagenomic approach could detect all targets inoculated at approximately 1 CFU/g flour to the species level. Discriminatory power was determined by simultaneous detection of dual inoculums of Salmonella and E. coli, absence of detection in control samples, and consistency in microbial flora composition of the same flour samples over several rounds of experiments. The total turnaround time for detection was approximately 20 h. Longer sequencing for up to 15 h enabled serotyping for many of the samples with more than 99% genome coverage, which could be subjected to other appropriate genetic analysis pipelines in less than a total of 36 h. IMPORTANCE Enterohemorrhagic Escherichia coli (EHEC) and Salmonella are of serious concern in low-moisture foods, including wheat flour and its related products, causing illnesses, outbreaks, and recalls. The development of advanced detection methods based on molecular principles of analysis is essential to incorporate into interventions intended to reduce the risk from these pathogens. In this work, a quasimetagenomic method based on real-time sequencing analysis and assisted by magnetic capture and DNA amplification was developed. This protocol is capable of detecting multiple Salmonella and/or E. coli organisms in the sample within less than a day, and it can also generate sufficient whole-genome sequences of the target organisms suitable for subsequent bioinformatics analysis. Multiplex detection and identification were accomplished in less than 20 h and additional whole-genome analyses of different nature were attained within 36 h, in contrast to the several days required in previous sequencing pipelines.

The objective of this prospective cohort study was to describe the relationship between exposure to antimicrobials, through both the milk diet and systemic therapy, and to describe antimicrobial resistance of fecal Escherichia coli in dairy calves pre- and postweaning. A convenience sample of 15 Minnesota dairy farms was chosen, representing 3 equal cohorts of milk diet fed to preweaned calves: medicated milk replacer (MMR), nonmedicated milk replacer (NMR), or pasteurized nonsaleable milk (PNM). Five newborn calves were enrolled on each farm, with fecal samples collected from each calf at 1, 3, 5, and 16 wk of age. After isolation, 3 colonies of E. coli were randomly selected from each sample to determine antimicrobial susceptibility by minimum inhibitory concentration (Sensititer, Thermo Scientific, Waltham, MA) to 8 antimicrobials in 8 classes. The isolate was given an antimicrobial resistance score (ARS) according to the number of antimicrobial classes to which it was resistant. Any isolate resistant to 3 or more antimicrobials was defined as being multidrug resistant (MDR). Relationships between ARS and MDR (dependent variables) and possible explanatory variables were analyzed using mixed multivariable linear and logistic regression models, respectively, with critical P-values adjusted for multiple contrasts. Seventy percent of isolates were resistant to sulfadimethoxine. For wk 1 and 3, the mean ARS values were greatest for fecal E. coli from calves fed MMR or PNM compared with NMR, with no difference in ARS values between the MMR and PNM groups at either time point. At wk 5, the mean ARS value was greatest for fecal E. coli from calves fed MMR (3.56 ± 0.45; mean ± SE), intermediate for calves fed PNM (2.64 ± 0.45), and lowest for calves fed NMR (1.54 ± 0.45). However, by wk 16, the mean ARS values were ≤1.0 and did not differ among milk diets. Evaluation of the proportion of isolates with MDR mirrored the results of the ARS analysis (MDR more prevalent in MMR and PNM groups preweaning; no difference among milk diets at 16 wk). There was a tendency for an increase in ARS at wk 5 (1.28 ± 0.70), and the odds for MDR in fecal E. coli were estimated to be 5.2 (95% confidence interval = 0.67, 35.7) and 101.1 (95% confidence interval = 1.15, >999.9) higher at wk 3 and 5 if the calf was treated with a systemic antimicrobial within the 14-d period before sampling. These findings suggest that exposure to antimicrobials through the milk diet or systemic therapy may result in a transient increase in resistance in fecal E. coli, but once the antimicrobial pressure is removed, susceptible E. coli are able to flourish again, resulting in an overall decrease in resistance.

Bacteriophages are considered a potential antimicrobial food intervention due to their ability to inactivate target bacteria in different environments. This study was undertaken to isolate, characterize, and identify a mixture of phages that could be used for control of Listeria monocytogenes. A total of 37 phages were isolated from raw sewage sludge using L. monocytogenes serotypes 4b, 1/2a and 1/2b strains. The host range of these phages was determined by spot-testing. Ten lytic phages were selected for further evaluation with efficiency of plating (EOP) analysis and characterization by pulsed field gel electrophoresis (PFGE). According to the spot tests and EOP results, the isolated phages against L. monocytogenes 4b strains were found to be capable of lysing a wider range of ribotypes. Also, three phages specific for 1/2a and 1/2b serotypes had similar lysis capabilities over a range of target Listeria with high EOP values between 0.5 and 1.0. PFGE analysis identified 5 distinct restriction profiles of the 10 selected phages whose DNA was digested with either EcoRI or HinDIII. Transmission electron microscopy (TEM) pictures revealed that five selected phages belonged to the Myoviridae and one phage to the Podoviridae family. Based on screening results, a phage cocktail (LP1) comprised of six lytic phages was used to inactivate a mixed culture of five L. monocytogenes strains. LP1 was able to lyse bacterial cells within 30–60 min at multiplicity of infection values (MOI, PFU/CFU) of 1000 and maintained the target cells under detection levels for 24 to 48 h at 4, 10, and 30 °C. These results suggested the LP1 phage collection contained effective and strongly lytic phages that may serve as antibacterial preparation to control L. monocytogenes of different serotypes.

Enterohaemorrhagic Escherichia coli (EHEC) serotype O157:H7 is carried asymptomatically by cattle gastrointestinal tract and the inclusion of distillers grains solids (DGS) in feed is thought to be a factor in the prevalence and persistence of EHEC O157 in a herd. The present study surveys the faecal prevalence of E. coli O157 in cattle processed at an abattoir in the Upper Midwest and its association with environmental factors and feeding practices. Faecal samples were collected from pre-processing cows during a 1-year period. E. coli O157 prevalence was estimated isolation of putative positives and confirmation of isolates by immunoassay and multiplex virulence genes PCR analysis. Overall, E. coli O157 was confirmed in 11.2% of samples. Prevalence during winter was the highest at 14% followed by summer (11.6%) and declined to less than 8% the rest of the year. Winter was the only season that had a statistically significant effect on prevalence. As a category unto itself, DGS feeding before arrival had no significant influence on faecal prevalence. However, we found a significant interaction of DGS feeding and summer. This observation is extremely relevant because it corroborates a previous study and suggests possible feeding practices to abate EHEC O157 presence during harvest.

Preservation technologies subject bacterial cells to different levels of stress, which in the most effective cases lead to their inactivation and death. The term “stress” can refer to any extracellular influence that threatens the ability of microorganisms to perform their living functions. The food preservation technologies designed to rapidly inactivate microbial cells include thermal processes, irradiation, high-pressure processing, and the use of strong oxidant compounds. Other technologies accomplish the preservation of foods by inhibiting growth; the most extensively used are low-temperature storage (refrigeration and freezing), reduction of moisture content (concentration and drying), control of ox-redox potential (use of controlled atmospheres and vacuum packaging), and acidification (fermentation and addition of organic acids). In nature, microorganisms are constantly exposed to similar changes in temperature, oxygen, moisture, light, pH, and chemical composition. Bacteria are able to survive thanks to a wide array of molecular responses that provide cellular protection against stresses. Bacteria are protected from changes in pH, temperature, oxidative conditions, solute concentrations, and pressure by a network of sophisticated global genetic regulatory systems and molecular stress responses specific to individual chemical or physical threats. The most important general regulators and specific genetic systems reported in representative foodborne pathogenic bacteria are highlighted in this chapter.

The control of Salmonella in low water activity foods poses a challenge for the food industry because of its thermal resistance. The use of surrogate bacteria in a food plant is considered a critical component to validate processing steps. The objective of this study was to evaluate the use of Pediococcus acidilactici ATCC 8042, a generally recognized as safe bacterium (GRAS), as potential surrogate for Salmonella in commercial toasted oats cereal (TOC) and peanut butter. P. acidilactici was compared to a five-serovar cocktail of Salmonella and Enterococcus faecium NRRL-B2354, separately. Cultures were inoculated into TOC and thermal kinetic parameters (δ, β) were determined at 80, 85, 90, and 95 °C using the Weibull model. In peanut butter, δ and β parameters were obtained at 63, 68, 73, and 77 °C. In TOC, the δ values (initial decimal reduction time) of P. acidilactici were 63 and 7 min at 80 and 95 °C, respectively, and at all four temperatures they were not significantly different from δ values of E. faecium. The δ value of Salmonella at 80 °C (139 min) was two-fold greater than the other two bacteria's values (p

Salmonella and enterohemorrhagic Escherichia coli (EHEC) are of serious concern in wheat flour and its related products but little is known on their survival and thermal death kinetics. This study was undertaken to determine their long-term viability and thermal inactivation kinetics in flour. Inoculation was performed using mixtures of EHEC serogroups O45, O121, O145 and Salmonella followed by storage at room temperature (23°C) or 35°C (for Salmonella). Plate counting on tryptic soy agar (TSA) and enrichment were used to assess long-term survival. For thermal studies, wheat flour samples were heated at 55, 60, 65, and 70°C and cell counts of EHEC and Salmonella were determined by plating. The δ-values were calculated using the Weibull model. At room temperature, EHEC serovars and Salmonella were quantifiable for 84 and 112 days, and were detectable for the duration of the experiment after 168 and 365 days, respectively. The δ-values were 2.0, 5.54, and 9.3 days, for EHEC O121, O45, and O145, respectively, and 9.7 days for Salmonella. However, the only significant difference among all values was the δ-value for Salmonella and serogroup O121 (p ≤ 0.05). At 35°C, Salmonella counts declined to unquantifiable levels after a week and were not detected upon enrichment after 98 days. Heat treatment of inoculated wheat flour at 55, 60, 65, and 70°C resulted in δ-value ranges of 20.0–42.9, 4.9–10.0, 2.4–3.2, and 0.2–1.6 min, respectively, for EHEC. The δ-values for Salmonella at those temperatures were 152.2, 40.8, 17.9, and 17.4 min, respectively. The δ-values obtained for Salmonella at each temperature were significantly longer than for EHEC (p ≤ 0.05). Weibull model was a good fit to describe the thermal death kinetics of Salmonella and EHEC O45, O121 and O145 in wheat flour. HIGHLIGHTS -EHEC and Salmonella can survive for extended periods of time in wheat flour.-Long-term storage inactivation curves of EHEC and Salmonella were similar.-EHEC was more sensitive to heat than Salmonella.-Weibull model was a good fit to describe thermal death kinetics of EHEC and Salmonella.-Flour storage at 35°C may be a feasible method for microbial reduction.

Current consumer preferences for both clean label food ingredients and convenience-based foods has provided a unique opportunity to explore the application of novel natural food preservatives in sous vide products. The anaerobic environment and relatively low thermal processing of the sous vide process creates a favorable environment for the survival, germination, and outgrowth of spore-forming bacterium Clostridium perfringens. The aim of this study was to identify effective novel natural ingredient formulations against C. perfringens and apply them within a vacuum-sealed sous vide chicken model exposed to abusive storage and chilling conditions. Among six commercial vinegar-based formulations, liquid vinegar with citrus extract (CE; 1.0%) and with lemon juice concentrate (LJC; 1.5%) were identified as the most effective at inhibiting three individual C. perfringens strains. Both reduced viable cell counts by 5 log CFU/mL (P

The presence of antibiotic-resistant bacteria in the food supply chain is a major concern. There is a great need to revalidate the effectiveness of the intervention strategies commonly used in food processing environments for multidrug-resistant strains. The purpose of this study was to determine the survival of antibiotic-resistant O26 and O103 Shiga-toxin producing Escherichia coli (STEC) strains to lactic acid (2.5, 3.5, 5%), sodium hypochlorite (0.2, 0.5, 1 ppm free chlorine), and heat (60, 61, 62.5 °C) treatments. Six strains from STEC serotypes O26 and O103 with three distinctive antibiotic-resistant profiles (susceptible, low and high resistance) were selected for the study. As expected, the rates of inactivation were faster at increasing biocide concentrations or temperature level. The Weibull model provided a better fit than the traditional log-linear model due to the appearance of nonlinear patterns. A 5% lactic acid treatment for 10 min reduced the population of all STEC strains by 5 log CFU/ml. Sodium hypochlorite treatment (1 ppm for 5 min) achieved a similar reduction. Thermal D values for O26 and O103 serotypes ranged from 0.37 to 2.09 and 0.37–1.71 min, respectively. No statistical differences (P > 0.05) in tolerance were found between the two STEC serotypes to the different treatments. The antibiotic profile was not related to the ability to tolerate any of the treatments. Only the susceptible strain showed a relative higher resistance to the lactic acid and lower resistance to sodium hypochlorite treatment. These results would contribute to assess the risk for the presence of STEC strains in food processing environments.

Hispanic style soft non-fermented cheeses, such as queso fresco (QF) have been linked to outbreaks and recalls. Salmonella is one of the main causes of these incidents. Due to lack of ripening or post-processing antimicrobial treatments, incorporating GRAS antimicrobials to production process may be a suitable approach to minimize microbial risk in QF. The aim of this study was to evaluate the efficiency of nisin (N), caprylic acid (CA) and trans-cinnamaldehyde (CN) as single or combined treatments to reduce Salmonella populations in QF during storage. Batches of QF were inoculated after curding with approx. 4 Log CFU/g of 5-strain cocktails of Salmonella and stored at 8 °C for 20 days. The final Salmonella counts in control samples ranged from 6.96 to 7.14 Log CFU/g. Application of CN at 0.6 g/kg inhibited Salmonella growth during storage, resulting in at least 3 Log CFU/g difference with the untreated controls (p

In this study, the changes in the global proteome of Salmonella in response to desiccation and thermal treatment were investigated by using an iTRAQ multiplex technique. A Salmonella enterica serovar Typhimurium strain was dried, equilibrated at high (1.0) and low (0.11) water activity (a(w)), and thermally treated at 75°C. The proteomes were characterized after every treatment. The proteomes of the different treatments differed in the expression of 175 proteins. On the basis of their proteomic expression profiles, the samples were clustered into two major groups, namely, “dry” samples and “moist” samples. The groups had different levels of proteins involved in DNA synthesis and transcription and in metabolic reactions, indicating that cells under either of the a(w) conditions need to strictly control energy metabolism, the rate of replication, and protein synthesis. The proteins with higher expression levels in moist samples were flagellar proteins (FlgEFGH), membrane proteins, and export systems (SecF, SecD, the Bam complex), as well as stress response proteins, suggesting that rehydration can trigger stress responses in moist cells. Dry samples had higher levels of ribosomal proteins, indicating that ribosomal proteins might be important for additional regulation of the cellular response, even when the synthesis of proteins is slowed down. At both a(w)s, no differences in protein expression were observed between the thermally treated samples and the nonheated cells. In conclusion, our study indicates that the preadaptation to a dry condition was linked to increased thermal tolerance, while reversion from a dry state to a moist state induced a significant change in protein expression, possibly linked to the observed loss of thermal tolerance. IMPORTANCE Salmonella enterica is able to survive in dry environments for very long periods. While it is well known that the initial exposure to desiccation is fundamental to trigger thermal tolerance in this organism, the specific physiological and molecular processes involved in this cross-protection phenomenon have not been fully characterized. Several studies have focused on the low-a(w) transcriptome of this pathogen when inoculated in different food matrices or on abiotic surfaces, but proteomic analyses have not been reported in the literature. Our study investigated the changes in proteomic expression in Salmonella enterica serovar Typhimurium during desiccation, exposure to low a(w), and thermal treatment. A better knowledge of the systems involved in the response to desiccation and thermal tolerance, as well as a better understanding of their interplay, is fundamental to identify the most effective combination of interventions to prevent Salmonella's contamination of foods.

Community-associated Clostridium difficile infection (CA-CDI) now accounts for approximately 50% of CDI cases in central Minnesota; animals and meat products are potential sources. From November 2011 to July 2013, we cultured retail meat products and fecal samples from food-producing and companion animals in central Minnesota for C. difficile by using standard methods. The resulting 51 C. difficile isolates, plus 30 archived local veterinary C. difficile isolates and 208 human CA-CDI case isolates from central Minnesota (from 2012) from the Minnesota Department of Health, were characterized molecularly, and source groups were compared using discriminant analysis. C. difficile was recovered from 0 (0%) of 342 retail meat samples and 51 (9%) of 559 animal fecal samples. Overall, the 81 animal source isolates and 208 human source isolates were highly diverse genetically. Molecular traits segregated extensively in relation to animal versus human origin. Discriminant analysis classified 95% of isolates correctly by source group; only five (2.5%) human source isolates were classified as animal source. These data do not support meat products or food-producing and companion animals as important sources of CA-CDI in the central Minnesota study region.

Wheat flour has been associated with outbreaks of enterohemorrhagic Escherichia coli (EHEC), but little is known on EHEC's survival during storage and thermal processing. The objective of this study was to determine long-term viability and thermal inactivation kinetics of EHEC serogroups O26, O103, O111, and O157. Wheat flour samples were inoculated with a cocktail of five strains of a single serogroup and stored at 23 and 35°C. Inoculated samples were heated at 55, 60, 65, and 70°C. Viability was determined by plate counting. Decimal reduction time ( D ) and first decimal reduction time (δ) values were calculated with log-linear and Weibull models, respectively. At 23°C, EHEC counts declined gradually for 84 days and samples tested positive from 84 to 280 days. The thermal resistance ( D and δ) values ranged from 7.5 to 8.2 and 3.1 to 5.3 days, respectively, but there were no significant differences among serogroups ( P ≤ 0.05). At 35°C, no EHEC was quantifiable by day 7 and no positive samples were detected after 49 days. Heating at 55 and 65°C resulted in δ-value ranges of 15.6 to 39.7 min and 3.0 to 3.9 min, respectively, with no significant difference among serogroups either. Z values were 12.6, 6.7, 10.2, and 13.4°C for O26, O103, O111, and O157, respectively. Thermal death kinetics of EHEC in flour were better described using the Weibull model. Survival and inactivation rates of four serogroups were remarkably similar. These findings indicated that all EHEC serovars tested remained viable for at least 9 months at room temperature and survived for up to 60 min at 70°C in wheat flour. IMPORTANCE Enterohemorrhagic Escherichia coli (EHEC) and Salmonella have recently caused several gastroenteritis outbreaks and recalls of wheat flour. Because EHEC can cause illness with very low doses and there is very scarce information regarding their ability to survive storage and heating in flour, the present study was undertaken to assess the long-term survival of EHEC serogroups O26, O103, O111, and O157 in flour. These findings are relevant, as we report that EHEC can survive for more than 9 months in wheat flour during storage. In addition, results obtained suggest that thermal inactivation at 65°C for 30 min or 2 months of storage at 35°C may be feasible strategies to mitigate the risk of most EHEC serovars in wheat flour.

The United States Food and Drug Administration and the Department of Agriculture jointly published the "Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables," which is used as a basis for Good Agricultural Practices (GAP) audits. To understand barriers to incorporation of GAP by Minnesota vegetable farmers, a mail survey completed in 2008 was validated with visits to a subset of the farms. This was done to determine the extent to which actual practices matched perceived practices. Two hundred forty-six producers completed the mail survey, and 27 participated in the on-farm survey. Over 75% of the on-farm survey respondents produced vegetables on 10 acres or less and had 10 or fewer employees. Of 14 questions, excellent agreement between on-farm interviews and mail survey responses was observed on two questions, four questions had poor or slight agreement, and eight questions had no agreement. Ninety-two percent of respondents by mail said "they took measures to keep animals and pests out of packing and storage buildings." However, with the on-site visit only 45% met this requirement. Similarly, 81% of respondents by mail said "measures were taken to reduce the risk of wild and/or domestic animals entering into fruit and vegetable growing areas." With direct observation, 70% of farms actually had taken measures to keep animals out of the growing areas. Additional, on-farm assessments were done regarding employee hygiene, training, presence of animals, water sources, and composting practices. This validation study demonstrated the challenge of creating nonleading and concise questions that are not open to broad interpretation from the respondents. If mail surveys are used to assess GAP, they should include open-ended questions and ranking systems to better assess farm practices. To provide the most accurate survey data for educational purposes or GAP audits, on-farm visits are recommended.

This study determined the effect of previously described phage cocktail (BEC8) on the inactivation kinetics of a mixture of Escherichia coli (EHEC) O157:H7 strains on food processing surface materials: stainless steel chip (SSC), ceramic tile chip (CTC) and high-density polyethylene chip (HDPEC). EHEC strains were combined and spot-inoculated on surfaces in dried or liquid form and BEC8 was applied and incubated at 12, 23, 30 and 37C. EHEC survival was determined on tryptic soy agar. D values ranged from 3.9 min at 37C to 46.7 min at 12C. Z values calculated for SSC, CTC and HDEPC resulted in 26.1, 23.7 and 26.7C for dry cells, respectively, and 23.2, 23.7 and 24.5C for liquid cells, respectively. There was a significant difference in the rate of bacterial inactivation between lower (12 and 23C) and higher temperatures (30 and 37C). These results indicated that BEC8 killed EHEC on hard surfaces rapidly following first-order kinetics. Practical Applications The effect of a previously described phage cocktail (BEC8) on the inactivation kinetics of a mixture of Escherichia coli (EHEC) O157:H7 strains applied on hard food processing surface materials was studied. The results indicated that phages killed EHEC on hard surfaces relatively rapidly following a predictable rate. However, one must consider the long times to achieve a 5-log reduction when initial cell counts are high. It would take approximately 2–4 h for a 5-log cfu reduction of liquid cells at 23C. Both the time length and the temperature of application must fit within the industry time scales.

The use of bacteriophages is considered as a viable alternative to chemical antimicrobials against foodborne pathogens. The objective of this study was to develop a collection of lytic bacteriophages which will be able to infect different pathogenic Salmonella enterica serovars. Phages were isolated from animal feces and sewage samples, purified, characterized morphologically and by DNA fingerprinting, and host ranges were determined. Spot test and efficiency of plaquing (EOP) data indicated that two phages, SEA1 and SEA2 had the broadest host range against Salmonella among all isolated phages. SEA2 was highly efficient to infect S. Typhimurium DT104 (0.5–1 EOP value). Only phage SSA1 was able to infect S. Montevideo. Transmission electron microscopy (TEM) revealed the phages in the collection were mostly (4 out of 6) Siphoviridae, while SEA1 and SEA2 were Myoviridae T4-like phages. SEA1 and SEA2 had the largest genome sizes in the collection, 190 and 170 kb, respectively. Pulsed field gel electrophoresis (PFGE) analysis demonstrated distinct digestion profiles with Eco RI for phages SSA1, STD3, STE3 and STF1. However, SEA1 and SEA2 shared a similar restriction enzyme (RE) digestion pattern with same morphotype, but distinct profiles in lysing Salmonella strains. These anti- Salmonella phages were highly host specific with few exceptions of lytic phages that were able to infect a wide variety of Salmonella . These phages have potential for use in applications controlling Salmonella on different matrices.

Electrochemically activated water (ECAW), also known as electrolyzed water, and ozonized water are typically effective in inactivating bacteria, but their generation typically uses high current and voltage. A few simpler antimicrobial technologies that are also based on the application of a mild electrical current have been recently marketed to food retail and service customers claiming to have sanitizing properties for controlling bacteria. The objective of this study was to determine the sanitizing effect of some of these commercial technologies on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica and compare them with sterile water, generated ECAW generated with a pilot size electrolyzing unit, and salt solutions sprayed using commercial device sprays. A concentration of 100 mg/L ECAW had sanitizing effects of at least 5 log CFU/mL reductions on liquid culture and more than 4 log CFU/coupon reductions for E. coli O157:H7, L. monocytogenes and Salmonella dried on stainless steel surface, respectively. No bacterial cells were detected by direct plate counting post-ECAW treatment. In contrast, the treatment of liquid cultures with any of the commercial technologies tested resulted in non-significant bacterial cell reductions greater than 0.5 log CFU/mL. Similarly, when cells had been dried on metal surfaces and treated with any of the water generated with those technologies, no reductions were observed. When the manufacturer's instructions were followed, the reduction of cells on surface was largely due to the physical removal by cloth-wiping after water fraction application. These results indicate that treatment with any of these portable technologies had no noticeable antimicrobial activity. These results would be helpful for guiding consumers when choosing a right sanitization to ensure food safety.

Lettuce and spinach are increasingly implicated in foodborne illness outbreaks due to contamination by Escherichia coli O157:H7. While this bacterium has been shown to colonize and survive on lettuce leaf surfaces, little is known about its interaction with the roots of growing lettuce plants. In these studies, a microarray analyses, mutant construction and confocal microscopy were used to gain an understanding of structure and function of bacterial genes involved in the colonization and growth of E. coli O157:H7 on lettuce roots. After three days of interaction with lettuce roots, 94 and 109 E. coli O157:H7 genes were significantly up- and down-regulated at least 1.5 fold, respectively. While genes involved in biofilm modulation (ycfR and ybiM) were significantly up-regulated, 40 of 109 (37%) of genes involved in protein synthesis were significantly repressed. E. coli O157:H7 was 2 logs less efficient in lettuce root colonization than was E. coli K12. We also unambiguously showed that a ΔycfR mutant of E. coli O157:H7 was unable to attach to or colonize lettuce roots. Taken together these results indicate that bacterial genes involved in attachment and biofilm formation are likely important for contamination of lettuce plants with Shiga toxin-producing E. coli strains.

Antibiotics are used in ethanol produc- tion to control bacteria from competing with yeast for nutrients during starch fermentation. However, there is no published scientifi c information on whether anti- biotic residues are present in distillers grains (DG), co-products from ethanol production, or whether they retain their biological activity. Therefore, the objectives of this study were to quantify concentrations of vari- ous antibiotic residues in DG and determine whether residues were biologically active. Twenty distillers wet grains and 20 distillers dried grains samples were col- lected quarterly from 9 states and 43 ethanol plants in the United States. Samples were analyzed for DM, CP, NDF, crude fat, S, P, and pH to describe the nutritional characteristics of the samples evaluated. Samples were also analyzed for the presence of erythromycin, peni- cillin G, tetracycline, tylosin, and virginiamycin M1, using liquid chromatography and mass spectrometry. Additionally, virginiamycin residues were determined, using a U.S. Food and Drug Administration-approved bioassay method. Samples were extracted and further analyzed for biological activity by exposing the sample extracts to 10 4 to 10 7 CFU/mL concentrations of sen- tinel bacterial strains Escherichia coli ATCC 8739 and Listeria monocytogenes ATCC 19115. Extracts that inhibited bacterial growth were considered to have biological activity. Physiochemical characteristics var- ied among samples but were consistent with previous fi ndings. Thirteen percent of all samples contained low (≤1.12 mg/kg) antibiotic concentrations. Only 1 sam- ple extract inhibited growth of Escherichia coli at 10 4 CFU/mL, but this sample contained no detectable con- centrations of antibiotic residues. No extracts inhibited Listeria monocytogenes growth. These data indicate that the likelihood of detectable concentrations of anti- biotic residues in DG is low; and if detected, they are found in very low concentrations. The inhibition in only 1 DG sample by sentinel bacteria suggests that antibiotic residues in DG were inactivated during the production process or are present in sublethal concentrations.

Here we investigated whether Salmonella enterica serovar Typhimurium ATCC 14028 was capable of internalizing in peanut seedpods and plants when exposed to inoculated soil and the edaphic factors that influenced uptake. Intact dry Virginia (DV) and fresh green Virginia (GV) seedpods were exposed to soil containing 6.5 Log (CFU/g) Salmonella under different soil moisture conditions. Internalization of S. Typhimurium into peanut plants germinated in inoculated soil was also examined with and without Bradyrhizobium (Arachis) sp.NC92. Salmonella counts recovered from GV seedpods were on average of 2.0 Log (CFU/pod) less than those recovered from DV seedpods. The internalization in DV pods was only observed at soil water content of 15% or greater in a loamy sand soil. S. Typhimurium was detected inside peanut plant tissues during most testing times. Cells were recovered from stem samples (3.5 Log CFU/g) at greater levels than it was observed for root (2.6 Log CFU/g) and leaf (1.7 Log CFU/g) samples. Overall, recovery of Salmonella from stem, root, and leaf samples were lower when B. NC92 was inoculated on seeds before sowing, but this trend was not significant. Our observations suggest possible routes of contamination of Salmonella into peanut products from soil.

Queso fresco, is a Hispanic non-fermented cheese highly susceptible to contamination with L. monocytogenes. This research was aimed to determine the effect of GRAS antimicrobial ingredients to control L. monocytogenes. Antimicrobials included caprylic acid (CA), Nisaplin® (N, 2.5% nisin), a mixture of sodium lactate and sodium diacetate (SL/SD), Lactococcus lactis sbp. lactis DPC 3147, monolaurin, and lactic acid (LA). Batches of queso fresco curds were inoculated with 104 CFU/g and stored at 4 °C for three weeks. During storage the count of L. monocytogenes reached 7 to 8 Log CFU/g in control samples. Most individual antimicrobial treatments resulted in less than 1 Log CFU/g reductions in final counts, with the exception of N (0.5 g/kg) and CA (2.9 g/kg) that caused more than 3 and 5 Log CFU/g differences with controls, respectively. Mixtures of ingredients were more effective in inhibiting L. monocytogenes growth, and treatments with N and CA consistently delivered 6 Log CFU/g less counts than controls. Supplementation of 12 g/kg LA to treatments with SL/SD (3%/0.22%) caused differences of more than 4 Log CFU/g in final Listeria populations. Samples treated with the binary mixtures of N and CA (0.5 and 0.7 g/kg, respectively) were evaluated in a consumer panel (n = 67). Panelists slightly preferred control and commercial over treated samples, but all samples were in average rated between “slightly liking” and “moderately liking.” These experiments indicated that combined use of antimicrobial ingredients may be an effective way to control the population of Listeria monocytogenes in queso fresco.

In this study, saxitoxin dihydrochloride in skim milk was reacted with sodium hydroxide and hydrogen peroxide to yield nontoxic 8-amino-6-hydroxymethyl-iminopurine-3(2H)-propionic acid (AHIPA), which was quantified by fluorescence spectroscopy using excitation and emission wavelengths of 330 and 425 nm, respectively. Samples of saxitoxin dihydrochloride (in 20% ethanol, vol/vol) were used as controls. The limits of detection of AHIPA, based on the concentration of saxitoxin prior to inactivation, were 5 and 10 μg/ml for the control and skim milk, respectively. These values are considerably below the concentration of saxitoxin that corresponds to the lethal dosage of 1 mg for an adult of average weight (70 kg). The inactivation of saxitoxin proceeded at a lower rate in skim milk than in the control, as its reaction rate constant was only 0.004 min(-1) compared with 0.011 min(-1) for the control. We were unable to detect AHIPA in 2% milk contaminated with saxitoxin because of possible interference from what we believed were products of secondary reactions involving milk fat and sodium hydroxide. Our results also indicated that the conversion of saxitoxin to AHIPA increased initially with temperature up to 40°C but decreased thereafter. We observed a decrease in the formation of AHIPA when the concentration of hydrogen peroxide was increased except at 22°C, where there was an initial increase in AHIPA formation between 1.2 and 2.4 mg/ml hydrogen peroxide but its formation decreased thereafter.

Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly and simply detect ricin and other bioterrisiom agents in complex food matrices such as milk. In this study, we demonstrated a rapid method that combined immunomagnetic separation (IMS) and surface-enhanced Raman spectroscopy (SERS) to detect ricin in whole milk. IMS was used to specifically capture the ricin out of the milk. Then, SERS was applied to analyze the IMS eluate mixed with silver dendrite nanosubstrates. This approach facilitated detection and quantification down to 4 μg/mL ricin in milk within 20 min, based on the results of principal component analysis and partial least squares analysis. The feasibility of using a portable Raman instrument shows great promise for on-site detection in a processing facility. Practical Application: The method described in this manuscript that combined IMS and SERS could be used for rapid detection of ricin and other protein toxins in complex food matrices such as milk within 20 min. The use of a portable Raman could facilitate the on-site detection in a processing facility.

Aims: The objective of this study was to isolate, identify and characterize a collection of lytic bacteriophages capable of infecting enterohaemorrhagic Escherichia coli (EHEC) serotypes. Methods and Results: Phages were isolated from dairy and cattle feedlot manure using E. coli O157, O26 and O111 strains as hosts. Phages were enriched from faecal slurries by culture in 10× trypticase soy broth at 37°C overnight. Phage plaques were obtained by mixing the filtered culture supernatant with molten tryptone agar containing the phage E. coli host strain, pouring the inoculated agar on top of cooled TS agar and incubating the culture overnight. Phages were purified from plaques and screened against additional E. coli and EHEC strains by the efficiency of plating method (EOP). Phage CEV2, and five other phages previously isolated, were able to lyse all of the 15 O157 strains tested with EOP values consistently above 0·001. Two phages were found to be highly effective against strains of E. coli O157 through EOP tests and against O26 strains through spot tests, but not against the O serogroup 111 strains. A cocktail of eight phage that lyse E. coli O157 strains resulted in >5 log CFU ml−1 reductions at 37°C. Multiplex-PCR revealed that none of these eight phages carried stx1, stx2, hlyA or eaeA genes. Conclusions: A cocktail of bacteriophages was capable of lysing most strains of two EHEC serotypes. Significance and Impact of the Study: This collection of phages can be combined and potentially used as an antimicrobial cocktail to inactivate E. coli strains from O serogroups 157 and 26 and reduce their incidence in the food chain.

A method for rapid detection of foreign protein contamination in complex food matrices is critically needed. Here we present a novel method that combines immunomagnetic separation (IMS) and surface-enhanced Raman scattering (SERS) to detect ovalbumin (OVA), an egg white protein, added into whole milk. IMS was used to specifically capture the OVA out of the milk. Then SERS was applied to analyze the IMS eluate using silver dendrites as the substrate. Two SERS sample preparation methods, namely solution based and substrate based, were used to prepare the IMS eluate for SERS analysis. Results show both methods were able to detect 1 µg OVA in 1 ml milk (1 part per million). Based on the results of principal component analysis and partial least-squares analysis, solution SERS was more capable of quantitative analysis, while substrate SERS was more sensitive for qualitative analysis. The total analytical time for IMS–SERS was less than 20 min, which satisfied the requirement of rapid detection in a milk processing facility. Copyright © 2011 John Wiley & Sons, Ltd.

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 has been recognized as a major foodborne pathogen responsible for frequent gastroenteritis outbreaks. Phages and essential oils can be used as a natural antimicrobial method to reduce bacterial pathogens from the food supply. The objective of this study was to determine the effect of a bacteriophage cocktail, BEC8, alone and in combination with the essential oil trans-cinnameldehyde (TC) on the viability of a mixture of EHEC O157:H7 strains applied on whole baby romaine lettuce and baby spinach leaves. The EHEC O157:H7 strains used were Nal(R) mutants of EK27, ATCC 43895, and 472. Exponentially growing cells from tryptic soy (TS) broth cultures were spot inoculated on leaves and dried. EHEC cells were placed at low, medium, and high inoculum levels (10(4), 10(5), and 10(6) CFU/mL, respectively). Appropriate controls, BEC8 (approx. 10(6) PFU/leaf), and TC (0.5% v/v) were applied on treated leaves. The leaves were incubated at 4, 8, 23, and 37 °C in Petri dishes with moistened filter papers. EHEC survival was determined using standard plate count on nalidixic acid (50 μg/mL) Sorbitol MacConkey agar. No survivors were detected when both leaves were treated with BEC8 or TC individually at low inoculum levels after 24 h at 23 and 37 °C. When the EHEC inoculum size increased and/or incubation temperature decreased, the efficacy of BEC8 and TC decreased. However, when the two treatments were combined, no survivors were detected after 10 min at all temperatures and inoculum levels on both leafy greens. These results indicated that the BEC8/TC combination was highly effective against EHEC on both leafy greens. This combination could potentially be used as an antimicrobial to inactivate EHEC O157:H7 and reduce their incidence in the food chain.

The brine shrimp lethality assay (BSLA) was used for rapid and non-specific detection of biological and chemical warfare agents at concentrations considerably below that which will cause harm to humans. Warfare agents detected include T-2 toxin, trimethylsilyl cyanide, and commercially available pesticides such as dichlorvos, diazinon, dursban, malathion, and parathion. The assay was performed by introducing 50 μL of milk or orange juice contaminated with each analyte into vials containing 10 freshly hatched brine shrimp nauplii in seawater. This was incubated at 28 °C for 24 h, after which mortality was determined. Mortality was converted to probits and the LC50 was determined for each analyte by plotting probits of mortality against analyte concentration (log10). Our findings were the following: (1) the lethal effects of toxins dissolved in milk were observed, with T-2 toxin being the most lethal and malathion being the least, (2) except for parathion, the dosage (based on LC50) of analyte in a cup of milk (200 mL) consumed by a 6-y-old (20 kg) was less than the respective published rat LD50 values, and (3) the BSLA was only suitable for detecting toxins dissolved in orange juice if incubation time was reduced to 6 h. Our results support the application of the BSLA for routine, rapid, and non-specific prescreening of liquid foods for possible sabotage by an employee or an intentional bioterrorist act. Practical Application: The findings of this study strongly indicate that the brine shrimp lethality assay can be adapted for nonspecific detection of warfare agents or toxins in food at any point during food production and distribution.

Foods have been identified as a potential target for bioterrorism due to their essential nature and global distribution. Foods produced in bulk have the potential to have large batches of product intentionally contaminated, which could affect hundreds or thousands of individuals. Bacillus anthracis spores are one potential bioterrorism agent that may survive pasteurization and remain viable throughout the shelf life of fruit juices and cause disease if consumed. This project examined B. anthracis spore survival in orange, apple, and grape juices, as well as wine. Samples of beverages were inoculated with spores of two nonpathogenic B. anthracis strains at approximately 10(6) CFU/ml, and the spore count was determined periodically during storage for 30 days at 4°C. After this time, the counts of survival spores never declined more than 1 log CFU/ml in any of the beverage types. These results indicate that spores can survive, with little to no loss in viability, for at least a month in fruit juices and wine.

This research was conducted to study the growth of Listeria monocytogenes inoculated on frankfurters stored at different conditions as a basis for a safety-based consume by shelf life date label. Three L. monocytogenes strains were separately inoculated at 10 to 20 CFU/cm2 onto frankfurters that were previously formulated with or without high pressure and with or without added 2% potassium lactate (PL) and 0.2% sodium diacetate (SD). Inoculated frankfurters were air or vacuum packaged; stored at 4, 8, or 12 degrees C; and L. monocytogenes and psychrotrophic plate counts were determined for 90, 60, and 45 days, respectively, or until the stationary phase was reached. The data (log CFU per square centimeter versus time) were fitted using the Baranyi-Roberts model to determine maximum growth rates and lag-phase time. The maximum growth rates and the lag time under each growth condition were used to calculate the time to reach 100-fold the initial Listeria population. In frankfurters lacking PL and SD, the count of all strains increased by 2 log after 18 to 50 days at 4 degrees C and 4 to 13 days at 8 degrees C. The growth was inhibited at 4 and 8 degrees C in frankfurters containing PL and SD, but one ribotype was capable of growing, with the time to reach 100-fold the initial Listeria population ranging from 19 to 35 days at 12 degrees C. In most cases, the time to reach 100-fold the initial Listeria population of L. monocytogenes was significantly longer in vacuum-packaged frankfurters as compared with air-packaged samples. Inclusion of PL and SD also inhibited the growth of psychrotrophs, but at all temperatures the psychrotrophic plate counts were greater than 4 log CFU/cm2 at the end of the experiments. These results indicated that despite the use of antimicrobials, certain L. monocytogenes strains could be capable of growing under storage-abuse conditions. Growth kinetics data could be useful for establishing a shelf life date label protocol under different handling scenarios.

The growth variability of three Listeria monocytogenes ribotypes in ready-to-eat (RTE) sliced uncured turkey breast and cured ham was studied under storage conditions that RTE foods are likely to encounter. Three product treatments studied were: (1) a control; (2) a formulation subjected to high pressure processing to reduce initial microbial load (HPP); (3) a formulation containing 2.0% potassium lactate and 0.2% sodium diacetate (PL/SD). After separate inoculation with individual L. monocytogenes ribotypes and packaging each treatment under air and vacuum, the packages were stored at 4, 8, or 12 degrees C and the counts of L. monocytogenes and psychrotrophic bacteria (PPC) were determined for several weeks. The Baranyi model was used to estimate lag times and growth rates. Significant effect of strain difference was noted in both sliced products (P

In a previous study, preparations of polyclonal antibodies (PAP) against Fusobacterium necrophorum (PAP-Fn) or Streptococcus bovis (PAP-Sb) were successful in decreasing ruminal counts of target bacteria and increasing ruminal pH in steers fed high-grain diets. The objective of this study was to evaluate the effects of feeding PAP-Fn or PAP-Sb on performance, carcass characteristics, and ruminal fermentation variables of feedlot steers. In Exp. 1, during 2 consecutive years, 226 or 192 Angus and Angus crossbred steers were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. When measured on a BW basis, steers fed only PAP-Sb had a greater G:F (P 0.10) to steers fed no PAP or only PAP-Sb. Steers receiving PAP-Fn (alone or in combination with PAP-Sb) had a decreased (P 0.10) were observed in any other carcass characteristics. In Exp. 2, sixteen ruminally cannulated Angus crossbred steers (BW = 665 +/- 86 kg) were fed a high-grain diet containing either PAP-Sb or PAP-Fn, or both. Feeding only PAP-Fn or PAP-Sb for 19 d decreased (P < 0.05) ruminal counts of S. bovis when compared with steers fed both or no PAP. The ruminal counts of F. necrophorum in steers fed PAP-Fn alone or in combination with PAP-Sb were decreased by 98% (P < 0.05) after 19 d, when compared with the counts in control steers. Mean daily ruminal pH was greater (P < 0.05) in steers fed both PAP when compared with feeding either or no PAP. Ruminal pH in the first 4 h after feeding was greater (P < 0.05) for steers receiving PAP-Fn alone or in combination with PAP-Sb. Steers receiving either PAP alone or in combination had less (P < 0.05) ruminal NH(3)-N concentrations in the first 4 h after feeding when compared with those of control steers. Polyclonal antibody preparations against S. bovis were effective in enhancing G:F of steers fed high-grain diets, but dressing percentage was decreased. Mechanisms of enhancement of G:F remain unknown but may be related to changes in ruminal counts of target bacteria and associated effects on ruminal fermentation products.

The milk supply is considered a primary route for a bioterrorism attack with Bacillus anthracis spores because typical high-temperature short-time (HTST) pasteurization conditions cannot inactivate spores. In the event of intentional contamination, an effective method to inactivate the spores in milk under HTST processing conditions is needed. This study was undertaken to identify combinations and concentrations of biocides that can inactivate B. anthracis spores at temperatures in the HTST range in less than 1 min. Hydrogen peroxide (HP), sodium hypochlorite (SH), and peroxyacetic acid (PA) were evaluated for their efficacy in inactivating spores of strains 7702, ANR-1, and 9131 in milk at 72, 80, and 85°C using a sealed capillary tube technique. Strains ANR-1 and 9131 were more resistant to all of the biocide treatments than strain 7702. Addition of 1,260 ppm SH to milk reduced the number of viable spores of each strain by 6 log CFU/ml in less than 90 and 60 s at 72 and 80°C, respectively. After neutralization, 1,260 ppm SH reduced the time necessary to inactivate 6 log CFU/ml (TTI6-log) at 80°C to less than 20 s. Treatment of milk with 7,000 ppm HP resulted in a similar level of inactivation in 60 s. Combined treatment with 1,260 ppm SH and 1,800 ppm HP inactivated spores of all strains in less than 20 s at 80°C. Mixing 15 ppm PA with milk containing 1,260 ppm SH resulted in TTI6-log of 25 and 12 s at 72 and 80°C, respectively. TTI6-log of less than 20 s were also achieved at 80°C by using two combinations of biocides: 250 ppm SH, 700 ppm HP, and 150 ppm PA; and 420 ppm SH (pH 7), 1,100 ppm HP, and 15 ppm PA. These results indicated that different combinations of biocides could consistently result in 6-log reductions in the number of B. anthracis spores in less than 1 min at temperatures in the HTST range. This information could be useful for developing more effective thermal treatment strategies which could be used in HTST milk plants to process contaminated milk for disposal and decontamination, as well as for potential protective measures.

This study compared the performance of four primary mathematical models to study the growth kinetics of Listeria monocytogenes ribotypes grown at low temperature so as to identify the best predictive model. The parameters of the best-fitting model were used to select the fastest growing strains with the shortest lag time and greatest growth rate. Nineteen food, human and animal L. monocytogenes isolates with distinct ribotype were grown at 4, 8, and 12 degrees C in tryptic soy broth and slurries prepared from cooked uncured sliced turkey breasts (with or without potassium lactate and sodium diacetate, PL/SD) and cooked cured frankfurters (with or without PL/SD). Separate regressions were performed on semi-logarithm growth curves to fit linear (based on Monod) and non-linear (Gompertz, Baranyi-Roberts, and Logistic) equations and performance of each model was evaluated using an F-test. No significant differences were found in the performance of linear and non-linear models, but the Baranyi model had the best fit for most growth curves. The maximum growth rate (MGR) of Listeria strains increased with the temperature. Similarly MGR was found significantly greater when no antimicrobials were present in the formulation of turkey or frankfurter products. The variability in lag times and MGRs in all media as determined by the Baranyi model was not consistent among strains. No single strain consistently had the fastest growth (shortest lag time, fastest MGR, or shortest time to increase 100-fold), but nine strains were identified as fastest growing strains under most growth conditions. The lack of association between serotype and fastest strain was also observed in the slurry media study. The fastest growing strains resulting from this study can be recommended for future use in L. monocytogenes challenge studies in delicatessen meat and poultry food matrices, so as to develop conservative pathogen growth predictions.

Microbiological analyses of fruits and vegetables produced by farms in Minnesota and Wisconsin were conducted to determine the prevalence of Escherichia coli in pre-harvest fruits and vegetables. During the 2003 and 2004 harvest seasons, 14 organic (certified by accredited organic agencies), 30 semi-organic (used organic practices but not certified) and 19 conventional farms were sampled to analyze 2029 pre-harvest produce samples (473 organic, 911 semi-organic, 645 conventional). Before each harvest season, a farmer survey was conducted to collect relevant information on farm management practices that might affect the risk of E. coli contamination in fresh produce. The use of animal wastes for fertilization of produce plants increased the risk of E. coli contamination in organic (OR=13.2, 95% CI=2.2-61.2, P-value

This study compared the antimicrobial susceptibility of Shiga toxin-producing Escherichia coli (STEC) isolates from organic dairy farms, conventional dairy farms, and Minnesota county fairs. A total of 83 STEC isolates (43 O157 and 40 non-O157 STEC) were tested for antimicrobial susceptibility as determined by the automated broth microdilution method. Resistance to tetracycline was identified in 19 (23%) isolates and to sulphadimethoxine in 40 (48%) isolates. Half of the STEC isolates were resistant to at least one antimicrobial agent. Resistance to at least one antimicrobial agent was observed in 18 (62%) isolates from conventional farms and in 11 (48%) isolates from organic farms. Resistance to at least one antimicrobial agent was more frequent in isolates from calves (77%) than from cows (39%). Multidrug resistant patterns were more common in non-O157 STEC than O157 STEC. This study provides data to document the degree of STEC antimicrobial resistance from dairy cattle sources in Minnesota. The use of antimicrobial agents on farms, and other environmental influences, may affect resistance patterns in isolates from cattle sources. Systematic surveillance of STEC from cattle could potentially detect emergence of antimicrobial resistance that may be spread to humans through the food chain.

In the current study, temperature dependent growth of Listeria monocytogenes strain H7776, with an initial inoculum level of approximately 0.1 CFU/mL or g, was modeled based on "time to detect" (TTD) using the Arrhenius equation. The activation energies (E(a)) obtained from specific growth rate and lag phase duration in tryptic soy broth (TSB) and frankfurters were compared. At 4 degrees C, the TTD for L. monocytogenes was 217 h in TSB and 48 h in portions of frankfurters. The TTD decreased as temperature increased from 4 to 36 degrees C in both culture media and frankfurters, and this relationship was modeled using the Arrhenius equation. Based on this model, the E(a) values for the TTD in TSB and frankfurters averaged 22.7 and 18.7 kcal/mol, respectively, and were not significantly different (p0.05). Linear regression was performed on the exponential part of the growth curve to evaluate specific growth rate constants at each temperature using the Monod model. The E(a) values were also calculated based on the specific growth rate and the lag phase of L. monocytogenes in TSB and frankfurters incubated in the same range of temperatures. The average E(a) values for the specific growth rates and the lag phase durations in TSB cultures were 19 and 21 kcal/mol, respectively. In frankfurters, the average E(a) values were slightly greater for both specific growth rate and lag phase duration (29 and 35 kcal/mol, respectively), but these values were not significantly different from the E(a) calculated for the TTD in each medium. These results indicate that the TTD concept can be used to develop and validate safety-based shelf life models.