Validation of a Simulated Commercial English Muffin Baking Process to control Salmonella Contamination

A validation study was conducted to investigate the effect of the English muffin baking process to control Salmonella contamination and to study the thermal inactivation kinetic parameters (D- and z-values) of Salmonella in English muffin dough. The unbleached bread flour was inoculated with 3 serovar Salmonella cocktail (Salmonella serovars viz., Newport, Typhimurium, and Senftenberg), and dried back to its preinoculated water activity levels with 7.46 ± 0.12 log CFU/g of Salmonella concentration. The Salmonella inoculated flour was used to prepare English muffin batter and baked at 204.4°C (400°F) for 18 min and allowed to cool at ambient air for 15 min. The English muffins reached 99 ± 0°C (211.96 ± 0.37°F) as their maximum mean internal temperature during baking. The pH and aw of English muffin dough were 5.01 ± 0.01 and 0.947 ± 0.003, respectively. At the end of the 18-min baking period, the Salmonella inoculated English muffins recorded a more than 5 log CFU/g reduction on the injury-recovery media. The D-values of 3 serovar cocktails of Salmonella at 55, 58.5, and 62°C were 42.0 ± 5.68, 15.6 ± 0.73, and 3.0 ± 0.32 min, respectively; and the z-value was 6.2 ± 0.59°C. The water activity (aw) of the English muffin crumb (0.947 ± 0.003 to 0.9557 ± 0.001) remained statistically unchanged during baking, whereas the aw of the muffin crust decreased significantly (0.947 ± 0.003 to 0.918 ± 0.002) by the end of 18 min of baking. This study validates and documents the first scientific evidence that baking English muffins at 204.4°C (400°F) for 18 min acts as an effective kill step by controlling Salmonella population by >5 log CFU/g.

Persistence comparison of two Shiga-toxin producing Escherichia coli (STEC) serovars during long-term storage and thermal inactivation in various wheat flours

Foodborne outbreaks associated with Shiga toxin-producing Escherichia coli (STEC) contaminated wheat flour have been an increasing food safety concern in recent decades. However, there is little literature aimed at investigating the impact of different flour types on the persistence of STEC during storage and thermal inactivation. Therefore, two serovars of STEC, O121 and O157, were selected to inoculate each of five different types of common wheat flours: whole wheat, bleached, unbleached, bread, and self-rising. Inoculated flours were examined for the stability of STEC during storage for up to 42 days at room temperature (RT) and aw ~0.56. Additionally, the thermal resistance of O121 and O157 under isothermal conditions at 60, 70, 80, and 90°C was analyzed for the inoculated flours. STEC storage persistence at RT was generally not affected by flour type, however, decreases of 1.2 and 2.4 log CFU/day within whole wheat flour for O121 and O157, respectively, were significantly lower than other flours. Though few differences were identified in relation to flour type, O121 exhibited significantly better survival rates than O157 during both equilibrium and storage periods. Compared to an approximate 6 log reduction in the population of O157, O121 population levels were reduced by a significantly lower amount (~3 log) during the entire storage period at RT. At each isothermal temperature, the impact of flour type on the thermal resistance capabilities of O121 or O157 was not a significant factor and resulted in similar survival curves regardless of serovar. Instead of exhibiting linear survival curves, both O121 and O157 displayed nonlinear curves with some shoulder/tail effect. Similar for both O121 and O157, the predicted decimal reduction time (D-value) decreased from approximately 25 min to around 8 min as the isothermal temperature increased from 60°C to 90°C. Results reported here can contribute to risk assessment models concerning contamination of STEC in wheat flour and add to our understanding of the impacts of flour type and STEC serovar on desiccation stability during storage and isothermal inactivation during thermal treatment.

Surface disinfection of wheat kernels using gas phase hydroxyl-radical processes: Effect on germination characteristics, microbial load, and functional properties

Wheat kernels harbor a diverse microflora that can negatively affect the suitability of the grains for further processing. To reduce surface microflora, a kernel disinfection method is required that does not affect grain functionality. Three different versions of gas phase hydroxyl-radical processes were compared with the common method for grain disinfection, that is, a bleach treatment. The gas phase hydroxyl-radicals are generated by the UV-C mediated degradation of hydrogen peroxide and/or ozone in a near water-free process. It was found that treating kernels with a bleach solution could reduce total aerobic count (TAC) and fungal count to below the level of enumeration. In comparison, the gas phase hydroxyl-radical treatment, that is, H2 O2 -UV-ozone treatment, could support a 1.3 log count reduction (LCR) in TAC and a 1.1 LCR in fungal count. The microbial load reduction for the wholemeal samples was less pronounced as endophytic microorganisms were less affected by all treatments, hinting at a limited penetration depth of the treatments. Despite reducing the microbial load on the kernel surface through the bleach and H2 O2 -UV-ozone treatments, none of these treatments resulted in a reduced microbial count on grains that underwent sprouting after the treatments. No negative effect on germination power or development of the seedling was observed for any of the treatments. The gluten aggregation behavior and xylanase activity of the wholemeal also remained unchanged after the gas phase hydroxyl-radical treatments. Our findings suggest that UV-H2 O2 -ozone treatment shows promise for dry-kernel disinfection, but further optimization of the processing parameters is required.

Foodborne disease outbreaks in flour and flour-based food products from microbial pathogens in the United States, and their health economic burden

The most comprehensive and inclusive estimates for the economic burden of foodborne illness yield values as high as $97.4 billion USD annually. However, broad incidence and cost estimates have limited use if they cannot be attributed to specific foods, for the purposes of food safety control. In this study, we estimated the economic burden of foodborne illnesses resulting from flour and flour-based food products in the United States from the years 2001 to 2021. The outbreak, illness burden, and health economic data are combined to generate these estimates. Our model combined outbreak data with published Centers for Disease Control and Prevention multipliers to estimate the annual number of illnesses associated with flour-borne pathogens. We then integrated illness severity data with an updated economic model that accounts for costs related to medical care, productivity loss, loss of life, along with the quality of life loss that entails pain and suffering. In total, 752 cases and 223 hospitalizations from flour-related illnesses were reported from 2001 to 2021, with an average of 37.6 cases of reported cases annually. However, the actual number of cases, accounting for underreporting and underdiagnosis, can be as high as 19,440 annually. Pathogens involved in these outbreaks are Salmonella, E. coli O157:H7, and E. coli O121. Our estimates suggest average annual economic losses, including healthy years of life lost, of $108 and $258 million using two alternative models.

Phagotrophic protists preserve antibiotic-resistant opportunistic human pathogens in the vegetable phyllosphere

Food safety of leafy greens is an emerging public health issue as they can harbor opportunistic human pathogens (OHPs) and expose OHPs to consumers. Protists are an integral part of phyllosphere microbial ecosystems. However, our understanding of protist-pathogen associations in the phyllosphere and their consequences on public health remains poor. Here, we examined phyllosphere protists, human pathogen marker genes (HPMGs), and protist endosymbionts from four species of leafy greens from major supermarkets in Xiamen, China. Our results showed that Staphylococcus aureus and Klebsiella pneumoniae were the dominant human pathogens in the vegetable phyllosphere. The distribution of HPMGs and protistan communities differed between vegetable species, of which Chinese chive possessed the most diverse protists and highest abundance of HPMGs. HPMGs abundance positively correlated with the diversity and relative abundance of phagotrophic protists. Whole genome sequencing further uncovered that most isolated phyllosphere protists harbored multiple OHPs which carried antibiotic resistance genes, virulence factors, and metal resistance genes and had the potential to HGT. Colpoda were identified as key phagotrophic protists which positively linked to OHPs and carried diverse resistance and virulence potential endosymbiont OHPs including Pseudomonas nitroreducens, Achromobacter xylosoxidans, and Stenotrophomonas maltophilia. We highlight that phyllosphere protists contribute to the transmission of resistant OHPs through internalization and thus pose risks to the food safety of leafy greens and human health. Our study provides insights into the protist-OHP interactions in the phyllosphere, which will help in food safety surveillance and human health.

Shiga toxin-producing Escherichia coli (STEC) and atypical enteropathogenic E. coli (aEPEC) in Swedish retail wheat flour

Wheat flour has been identified as the source of multiple outbreaks of gastrointestinal disease caused by shiga toxin-producing Escherichia coli (STEC). We have investigated the presence and genomic characteristics of STEC and related atypical enteropathogenic E. coli (aEPEC) in 200 bags of Swedish-produced retail wheat flour, representing 87 products and 25 brands. Samples were enriched in modified tryptone soya broth (mTSB) and screened with real-time PCR targeting stx₁, stx₂ and eae, and the serogroups O157, O121 and O26. Isolation was performed by immunomagnetic separation (IMS) for suspected STEC/aEPEC O157, O121 and O26, and by screening pools of colonies for other STEC. Real-time PCR after enrichment revealed 12 % of samples to be positive for shiga toxin genes (stx₁ and/or stx₂) and 11 % to be positive for intimin (eae). Organic production, small-scale production or whole grain did not significantly influence shiga toxin gene presence or absence in a generalized linear mixed model analysis. Eight isolates of STEC were recovered, all of which were intimin-negative. Multiple serotype/sequence type/shiga toxin subtype combinations that have also been found in flour samples in other European countries were recovered. Most STEC types recovered were associated with sporadic cases of STEC among humans in Sweden, but no types known to have caused outbreaks or severe cases of disease (i.e. haemolytic uraemic syndrome) were found. The most common finding was O187:H28 ST200 with stx_2g, with possible links to cervid hosts. Wildlife associated with crop damage is a plausible explanation for at least some of the surprisingly high frequency of STEC in wheat flour.

Impact of Quality Improvement and Milling Innovations on Durum Wheat and End Products

There are long-standing established intrinsic quality requirements of end products made from durum wheat semolina, with color, textural, and cooking properties of pasta and couscous representing persistent key attributes for consumers. Over time, traditional efforts to advance development in these areas with respect to raw material, equipment, and process improvements have been influenced by growing awareness of issues around food safety, health and nutrition, and climate change, necessitating that development strategies incorporate specific considerations relating to safety, traceability, and sustainability. We examined improvements in durum wheat quality and innovations in milling and the resulting impact on product quality in light of these considerations, which are now fundamental to the planning and development of any food process, as required by consumers and regulators alike.

Delayed lactose utilization among Shiga toxin-producing Escherichia coli of serogroup O121

Two outbreaks of Shiga toxin-producing Escherichia coli O121:H19 associated with wheat flour, in the United States of America and Canada, involved strains with an unusual phenotype, delayed lactose utilization (DLU). These strains do not ferment lactose when initially cultured on MacConkey agar (MAC), but lactose fermentation occurs following subculture to a second plate of MAC. The prevalence of DLU was determined by examining the β-galactosidase activity of 49 strains of E. coli O121, and of 37 other strains of E. coli. Twenty four of forty three O121:H19 and one O121:NM displayed DLU. Two strains (O121:NM and O145:H34) did not have detectable β-galactosidase activity. β-glucuronidase activity of O121 strains was also determined. All but six DLU strains had normal β-glucuronidase activity. β-glucuronidase activity was suppressed on MAC for 17 of 23 O121 non-DLU strains. Genomic analysis found that DLU strains possessed an insertion sequence, IS600 (1267 bp), between lacZ (β-galactosidase) and lacY (β-galactoside permease), that was not present in strains exhibiting normal lactose utilization. The insert might reduce the expression of β-galactoside permease, delaying import of lactose, resulting in the DLU phenotype. The high probability of DLU should be considered when using lactose-containing media for the isolation of STEC O121.

Biscuit Contaminants, Their Sources and Mitigation Strategies: A Review

The scientific literature is rich in investigations on the presence of various contaminants in biscuits, and of articles aimed at proposing innovative solutions for their control and prevention. However, the relevant information remains fragmented. Therefore, the objective of this work was to review the current state of the scientific literature on the possible contaminants of biscuits, considering physical, chemical, and biological hazards, and making a critical analysis of the solutions to reduce such contaminations. The raw materials are primary contributors of a wide series of contaminants. The successive processing steps and machinery must be monitored as well, because if they cannot improve the initial safety condition, they could worsen it. The most effective mitigation strategies involve product reformulation, and the use of alternative baking technologies to minimize the thermal load. Low oxygen permeable packaging materials (avoiding direct contact with recycled ones), and reformulation are effective for limiting the increase of contaminations during biscuit storage. Continuous monitoring of raw materials, intermediates, finished products, and processing conditions are therefore essential not only to meet current regulatory restrictions but also to achieve the aim of banning dietary contaminants and coping with related diseases.

Hypothesis Generation During Foodborne-Illness Outbreak Investigations

Hypothesis generation is a critical, but challenging, step in a foodborne outbreak investigation. The pathogens that contaminate food have many diverse reservoirs, resulting in seemingly limitless potential vehicles. Identifying a vehicle is particularly challenging for clusters detected through national pathogen-specific surveillance, because cases can be geographically dispersed and lack an obvious epidemiologic link. Moreover, state and local health departments could have limited resources to dedicate to cluster and outbreak investigations. These challenges underscore the importance of hypothesis generation during an outbreak investigation. In this review, we present a framework for hypothesis generation focusing on 3 primary sources of information, typically used in combination: 1) known sources of the pathogen causing illness; 2) person, place, and time characteristics of cases associated with the outbreak (descriptive data); and 3) case exposure assessment. Hypothesis generation can narrow the list of potential food vehicles and focus subsequent epidemiologic, laboratory, environmental, and traceback efforts, ensuring that time and resources are used more efficiently and increasing the likelihood of rapidly and conclusively implicating the contaminated food vehicle.

Thermal inactivation of Salmonella during hard and soft cookies baking process

This study validated a simulated commercial baking processes for hard and soft cookies to control Salmonella, and determined D- and z-values of 7-serotype Salmonella (Newport, Senftenberg, Tennessee, Typhimurium, and three isolates from dry pet food) cocktail in cookie doughs. Cookie doughs were prepared using flour mist-inoculated with the Salmonella cocktail. Hard and soft cookies were baked at 185 °C for 16 min and 165.6 °C for 22 min, respectively, followed by 30 min of ambient air cooling. D-values of the cocktail in cookie doughs were determined using thermal-death-time disks. Studies were designed as randomized complete blocks with three replications as blocks (α = 0.05). Salmonella populations decreased by > 5 log CFU/g in hard and soft cookies at 11.5 and 20.5 min of baking, respectively. Salmonella was not detected in hard cookies at the end of baking (as determined by enrichment), whereas in soft cookies, 0.6 log CFU/g Salmonella was present at the end of baking and cooling. Salmonella D-values in hard cookie dough at 60, 65 and 70 °C were 59.6, 28.1 and 11.9 min, respectively; while in soft cookie dough they were 62.3, 28.6 and 14.4 min, respectively. The Salmonella z-values in hard and soft cookie doughs were 14.5 and 15.8 °C, respectively.

Shiga Toxin-Producing Escherichia coli in Wheat Grains: Detection and Isolation by Polymerase Chain Reaction and Culture Methods

Shiga toxin-producing Escherichia coli (STEC) are major foodborne pathogens and seven serogroups, O26, O45, O103, O111, O121, O145, and O157, often called top-7 STEC, account for the majority of the STEC-associated human illnesses in the United States. Two Shiga toxins, Shiga toxins 1 and 2, encoded by stx1 and stx2 genes, are major virulence factors that are involved in STEC infections. Foodborne STEC infections have been linked to a variety of foods of both animal and plant origin, including products derived from cereal grains. In recent years, a few STEC outbreaks have been linked to contaminated wheat flour. The microbiological quality of the wheat grains is a major contributor to the safety of wheat flour. The objective of the study was to utilize polymerase chain reaction (PCR)- and culture-based methods to detect and isolate STEC in wheat grains. Wheat grain samples (n = 625), collected from different regions of the United States, were enriched in modified buffered peptone water with pyruvate (mBPWp) or E. coli (EC) broth, and they were then subjected to PCR- and culture-based methods to detect and isolate STEC. Wheat grains enriched in EC broth yielded more samples positive for stx genes (1.6% vs. 0.32%) and STEC serogroups (5.8% vs. 2.4%) than mBPWp. The four serogroups of top-7 detected and isolated were O26, O45, O103, and O157 and none of the isolates was positive for the Shiga toxin genes. A total of five isolates that carried the stx2 gene were isolated and identified as serogroups O8 (0.6%) and O130 (0.2%). The EC broth was a better medium to enrich wheat grains than mBPWp for the detection and isolation of STEC. The overall prevalence of virulence genes and STEC serogroups in wheat grains was low. The stx2-positive serogroups isolated, O8 and O130, are not major STEC pathogens and have only been implicated in sporadic infections in animals and humans.

Significance of Sodium Bisulfate (SBS) Tempering in Reducing the Escherichia coli O121 and O26 Load of Wheat and Its Effects on Wheat Flour Quality

The occurrence of recalls involving pathogenic Escherichia coli-contaminated wheat flours show the need for incorporating antimicrobial interventions in wheat milling. The objectives of this study were to assess the efficacy of sodium bisulfate (SBS) tempering in reducing E. coli O121 (ATCC 2219) and O26 (ATCC 2196) wheat load and to evaluate the impact of effective (≥3.0 log reductions) SBS treatments on wheat flour quality. Wheat grains were inoculated with E. coli (~6 log CFU/g) and tempered (17% moisture, 24 h) using the following SBS concentrations (%wheat basis): 0, 0.5, 0.75, 1.0, 1.25, and 1.5% SBS. Reductions in E. coli O121 and O26 wheat load at different time intervals (0.5, 2, 6, 12, 18, and 24 h) during tempering were evaluated. The addition of SBS during tempering resulted in E. coli (O121 and O26) log reductions of 2.0 (0.5% SBS) to >4.0 logs (1.5% SBS) (p ≤ 0.05). SBS tempering (1.25 and 1.5% SBS) produced acidic wheat flours (pH = 4.51–4.60) but had comparable wheat flour properties in terms of composition, dough, and bread-making properties relative to the control (0% SBS). SBS tempering reduced the E. coli O121 and O26 load of wheat after tempering with minimal effects on wheat flour quality.

Acute Bacterial Gastroenteritis

Acute bacterial gastroenteritis is among the most common infections worldwide, with millions of infections annually in the United States. Much of the illness is foodborne, occurring as both sporadic cases and large multistate outbreaks. Pathogen evolution through genetic exchange of virulence traits and antibiotic resistance determinants poses challenges for empiric therapy. Culture-independent diagnostic tests in clinical laboratories afford rapid diagnosis and expanded identification of pathogens. However, cultures remain important to generate sensitivity data and strain archiving for outbreak investigations. Most infections are self-limited, permitting judicious selection of antibiotic use in more severe forms of illness.

Visible light-activated ZnO nanoparticles for microbial control of wheat crop

Every year 15-50% of cereals all around the world are lost due to fungal contamination and deterioration. In addition, 25% of crops, which are used for human and animal consumption, are contaminated with mycotoxins. It is obvious, that more effective and sustainable technologies for better microbial control of crops are required. For this purpose we evaluated antibacterial and antifungal activity of ZnO nanoparticles (NPs) (10^-3-5 × 10^-3M) activated with visible light (405 nm, 18-30 J/cm²). Obtained data indicated that this treatment can inactivate human pathogen E. coli B by 6 log CFU without any possibility to regrowth after treatment. Wheat pathogen Fusarium oxysporum was inactivated by 51.7%. Results indicated that reactive oxygen species took place in the mechanisms of inactivation. Moreover, visible light activated ZnO NPs reduced the population of mesophiles on the surface of grains by 2.5 log CFU/g, inoculated E. coli- by 2.0 log CFU/g and naturally distributed fungi-by 2.1 log CFU/g. This treatment had no impact on visual quality of grains, did not inhibit grain germination rate and slightly promoted grain seedling growth. Concluding, the use of visible light driven photocatalysis in ZnO nanoparticles has huge potential to control plant pathogens, reduce food-borne diseases and subsequently enhance the sustainability in agriculture, meeting the increasing demands of a growing world population.

Genetic diversity and pathogenic potential of Shiga toxin-producing Escherichia coli (STEC) derived from German flour

Shiga toxin-producing Escherichia coli (STEC) can cause severe human illness, which are frequently linked to the consumption of contaminated beef or dairy products. However, recent outbreaks associated with contaminated flour and undercooked dough in the United States and Canada, highlight the potential of plant based food as transmission routes for STEC. In Germany STEC has been isolated from flour, but no cases of illness have been linked to flour. In this study, we characterized 123 STEC strains isolated from flour and flour products collected between 2015 and 2019 across Germany. In addition to determination of serotype and Shiga toxin subtype, whole genome sequencing (WGS) was used for isolates collected in 2018 to determine phylogenetic relationships, sequence type (ST), and virulence-associated genes (VAGs). We found a high diversity of serotypes including those frequently associated with human illness and outbreaks, such as O157:H7 (stx2c/d, eae), O145:H28 (stx2a, eae), O146:H28 (stx2b), and O103:H2 (stx1a, eae). Serotypes O187:H28 (ST200, stx2g) and O154:H31 (ST1892, stx1d) were most prevalent, but are rarely linked to human cases. However, WGS analysis revealed that these strains, as well as, O156:H25 (ST300, stx1a) harbour high numbers of VAGs, including eae, nleB and est1a/sta1. Although STEC-contaminated flour products have yet not been epidemiologically linked to human clinical cases in Germany, this study revealed that flour can serve as a vector for STEC strains with a high pathogenic potential. Further investigation is needed to determine the sources of STEC contamination in flour and flour products particularly in regards to these rare serotypes.

Models for factors influencing pathogen survival in low water activity foods from literature data are highly significant but show large unexplained variance

Factors that control pathogen survival in low water activity foods are not well understood and vary greatly from food to food. A literature search was performed to locate data on the survival of foodborne pathogens in low-water activity (<0.70) foods held at temperatures <37 °C. Data were extracted from 67 publications and simple linear regression models were fit to each data set to estimate log linear rates of change. Multiple linear stepwise regression models for factors influencing survival rate were developed. Subset regression modeling gave relatively low adjusted R² values of 0.33, 0.37, and 0.48 for Salmonella, E. coli and L. monocytogenes respectively, but all subset models were highly significant (p < 1.0e-9). Subset regression models showed that Salmonella survival was significantly (p < 0.05) influenced by temperature, serovar and strain type, water activity, inoculum preparation method, and inoculation method. E. coli survival was significantly influenced by temperature, water activity, and inoculum preparation. L. monocytogenes survival was significantly influenced by temperature, serovar and strain type, and inoculum preparation method. While many factors were highly significant (p < 0.001), the high degrees of variability show that there is still much to learn about the factors which govern pathogen survival in low water activity foods.

Investigations of Possible Multistate Outbreaks of Salmonella, Shiga Toxin-Producing Escherichia coli, and Listeria monocytogenes Infections - United States, 2016

PROBLEM/CONDITION

Salmonella, Shiga toxin-producing Escherichia coli (STEC), and Listeria monocytogenes are the leading causes of multistate foodborne disease outbreaks in the United States. Responding to multistate outbreaks quickly and effectively and applying lessons learned about outbreak sources, modes of transmission, and risk factors for infection can prevent additional outbreak-associated illnesses and save lives. This report summarizes the investigations of multistate outbreaks and possible outbreaks of Salmonella, STEC, and L. monocytogenes infections coordinated by CDC during the 2016 reporting period.

PERIOD COVERED

2016. An investigation was considered to have occurred in 2016 if it began during 2016 and ended on or before March 31, 2017, or if it began before January 1, 2016, and ended during March 31, 2016-March 31, 2017.

DESCRIPTION OF SYSTEM

CDC maintains a database of investigations of possible multistate foodborne and animal-contact outbreaks caused by Salmonella, STEC, and L. monocytogenes. Data were collected by local, state, and federal investigators during the detection, investigation and response, and control phases of the outbreak investigations. Additional data sources used for this report included PulseNet, the national molecular subtyping network based on isolates uploaded by local, state, and federal laboratories, and the Foodborne Disease Outbreak Surveillance System (FDOSS), which collects information from state, local, and territorial health departments and federal agencies about single-state and multistate foodborne disease outbreaks in the United States. Multistate outbreaks reported to FDOSS were linked using a unique outbreak identifier to obtain food category information when a confirmed or suspected food source was identified. Food categories were determined and assigned in FDOSS according to a classification scheme developed by CDC, the Food and Drug Administration (FDA), and the U.S. Department of Agriculture Food Safety and Inspection Service (FSIS) in the Interagency Food Safety Analytics Collaboration. A possible multistate outbreak was determined by expert judgment to be an outbreak if supporting data (e.g., temporal, geographic, demographic, dietary, travel, or food history) suggested a common source. A solved outbreak was an outbreak for which a specific kind of food or animal was implicated (i.e., confirmed or suspected) as the source. Outbreak-level variables included number of illnesses, hospitalizations, cases of hemolytic uremic syndrome (HUS), and deaths; the number of states with illnesses; date of isolation for the earliest and last cases; demographic data describing patients associated with a possible outbreak (e.g., age, sex, and state of residence); the types of data collected (i.e., epidemiologic, traceback, or laboratory); the outbreak source, mode of transmission, and exposure location; the name or brand of the source; whether the source was suspected or confirmed; whether a food was imported into the United States; the types of regulatory agencies involved; whether regulatory action was taken (and what type of action); whether an outbreak was publicly announced by CDC via website posting; beginning and end date of the investigation; and general comments about the investigation. The number of illnesses, hospitalizations, cases of HUS, and deaths were characterized by transmission mode, pathogen, outcome (i.e., unsolved, solved with suspected source, or solved with confirmed source), source, and food or animal category.

RESULTS

During the 2016 reporting period, 230 possible multistate outbreaks were detected and 174 were investigated. A median of 24 possible outbreaks was under investigation per week, and investigations were open for a median of 37 days. Of these 174 possible outbreaks investigated, 56 were excluded from this analysis because they occurred in a single state, were linked to international travel, or were pseudo-outbreaks (e.g., a group of similar isolates resulting from laboratory media contamination rather than infection in patients). Of the remaining 118 possible multistate outbreaks, 50 were determined to be outbreaks and 39 were solved (18 with a confirmed food source, 10 with a suspected food source, 10 with a confirmed animal source, and one with a suspected animal source). Sprouts were the most commonly implicated food category in solved multistate foodborne outbreaks (five). Chicken was the source of the most foodborne outbreak-related illnesses (134). Three outbreaks involved novel food-pathogen pairs: flour and STEC, frozen vegetables and L. monocytogenes, and bagged salad and L. monocytogenes. Eleven outbreaks were attributed to contact with animals (10 attributed to contact with backyard poultry and one to small turtles). Thirteen of 18 multistate foodborne disease outbreaks with confirmed sources resulted in product action, including 10 outbreaks with recalls, two with market withdrawals, and one with an FSIS public health alert. Twenty outbreaks, including 11 foodborne and nine animal-contact outbreaks, were announced to the public by CDC via its website, Facebook, and Twitter. These announcements resulted in approximately 910,000 webpage views, 55,000 likes, 66,000 shares, and 5,800 retweets.

INTERPRETATION

During the 2016 reporting period, investigations of possible multistate outbreaks occurred frequently, were resource intensive, and required a median of 37 days of investigation. Fewer than half (42%) of the 118 possible outbreaks investigated were determined to have sufficient data to meet the definition of a multistate outbreak. Moreover, of the 50 outbreaks with sufficient data, approximately three fourths were solved.

PUBLIC HEALTH ACTION

Close collaboration among CDC, FDA, FSIS and state and local health and agriculture partners is central to successful outbreak investigations. Identification of novel outbreak sources and trends in sources provides insights into gaps in food safety and safe handling of animals, which helps focus prevention strategies. Summarizing investigations of possible multistate outbreaks can provide insights into the investigative process, improve future investigations, and help prevent illnesses. Although identifying and investigating possible multistate outbreaks require substantial resources and investment in public health infrastructure, they are important in determining outbreak sources and implementing prevention and control measures.

The use of multiple hypothesis-generating methods in an outbreak investigation of Escherichia coli O121 infections associated with wheat flour, Canada 2016-2017

A Canadian outbreak investigation into a cluster of Escherichia coli O121 was initiated in late 2016. When initial interviews using a closed-ended hypothesis-generating questionnaire did not point to a common source, cases were centrally re-interviewed using an open-ended approach. The open-ended interviews led cases to describe exposures with greater specificity, as well as food preparation activities. Data collected supported hypothesis generation, particularly with respect to flour exposures. In March 2017, an open sample of Brand X flour from a case home, and a closed sample collected at retail of the same brand and production date, tested positive for the outbreak strain of E. coli O121. In total, 76% (16/21) of cases reported that they used or probably used Brand X flour or that it was used or probably was used in the home during their exposure period. Crucial hypothesis-generating techniques used during the course of the investigation included a centralised open-ended interviewing approach and product sampling from case homes. This was the first outbreak investigation in Canada to identify flour as the source of infection.

Chronological set of E. coli O157:H7 bovine strains establishes a role for repeat sequences and mobile genetic elements in genome diversification

Background

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is a significant foodborne pathogen that resides asymptomatically within cattle and other ruminants. The EHEC genome harbors an extensive collection of mobile genetic elements (MGE), including multiple prophage, prophage-like elements, plasmids, and insertion sequence (IS) elements.

Results

A chronological collection of EHEC strains (FRIK804, FRIK1275, and FRIK1625) isolated from a Wisconsin dairy farm (farm X) comprised a closely related clade genetically differentiated by structural alterations to the chromosome. Comparison of the FRIK804 genome with a reference EHEC strain Sakai found a unique prophage like element (PLE, indel 1) and an inversion (1.15 Mb) situated symmetrically with respect to the terminus region. Detailed analysis determined the inversion was due to homologous recombination between repeat sequences in prophage. The three farm X strains were distinguished by the presence or absence of indel 3 (61 kbp) and indel 4 (48 kbp); FRIK804 contained both of these regions, FRIK1275 lacked indel 4, and indels 3 and 4 were both absent in FRIK1625. Indel 3 was the stx2 prophage and indel 4 involved a deletion between two adjacent prophage with shared repeat sequences. Both FRIK804 and FRIK1275 produced functional phage while FRIK1625 did not, which is consistent with indel 3. Due to their involvement in recombination events, direct and inverted repeat sequences were identified, and their locations mapped to the chromosome. FRIK804 had a greater number and overall length of repeat sequences than E. coli K12 strain MG1655. Repeat sequences were most commonly associated with MGE.

Conclusions

This research demonstrated that three EHEC strains from a Wisconsin dairy farm were closely related and distinguished by variability within prophage regions and other MGE. Chromosome alterations were associated with recombination events between repeat sequences. An inventory of direct and inverted repeat sequences found a greater abundance and total length of repeat sequences in the EHEC strains compared to E. coli strain MG1655. The locations of the repeat sequences were biased towards MGE. The findings from this study expand our understanding of the precise molecular events and elements that contributed to genetic diversification of wild-type EHEC in the bovine and farm environments.

Salmonella enterica and Escherichia coli in Wheat Flour: Detection and Serotyping by a Quasimetagenomic Approach Assisted by Magnetic Capture, Multiple-Displacement Amplification, and Real-Time Sequencing

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 legacy of bacterial invasions on soil native communities

Soil microbial communities are often not resistant to the impact caused by microbial invasions, both in terms of structure and functionality, but it remains unclear whether these changes persist over time. Here, we used three strains of Escherichia coli O157:H7 (E. coli O157:H7), a species used for modelling bacterial invasions, to evaluate the resilience of the bacterial communities from four Chinese soils to invasion. The impact of E. coli O157:H7 strains on soil native communities was tracked for 120 days by analysing bacterial community composition as well as their metabolic potential. We showed that soil native communities were not resistant to invasion, as demonstrated by a decline in bacterial diversity and shifts in bacterial composition in all treatments. The resilience of native bacterial communities (diversity and composition) was inversely correlated with invader's persistence in soils (R² = 0.487, p < 0.001). Microbial invasions also impacted the functionality of the soil communities (niche breadth and community niche), the degree of resilience being dependent on soil or native community diversity. Collectively, our results indicate that bacteria invasions can potentially leave a footprint in the structure and functionality of soil communities, indicating the need of assessing the legacy of introducing exotic species in soil environments.

Formation and Control of the Viable but Non-culturable State of Foodborne Pathogen Escherichia coli O157:H7

As a common foodborne pathogen, Escherichia coli O157:H7 produces toxins causing serious diseases. However, traditional methods failed in detecting E. coli O157:H7 cells in the viable but non-culturable (VBNC) state, which poses a threat to food safety. This study aimed at investigating the formation, control, and detection of the VBNC state of E. coli O157:H7. Three factors including medium, salt, and acid concentrations were selected as a single variation. Orthogonal experiments were designed with three factors and four levels, and 16 experimental schemes were used. The formation of the VBNC state was examined by agar plate counting and LIVE/DEAD^® BacLight^TM bacterial viability kit with fluorescence microscopy. According to the effects of environmental conditions on the formation of the VBNC state of E. coli O157:H7, the inhibition on VBNC state formation was investigated. In addition, E. coli in the VBNC state in food samples (crystal cake) was detected by propidium monoazide-polymerase chain reaction (PMA-PCR) assays. Acetic acid concentration showed the most impact on VBNC formation of E. coli O157:H7, followed by medium and salt concentration. The addition of 1.0% acetic acid could directly kill E. coli O157:H7 and eliminate its VBNC formation. In crystal cake, 25, 50, or 100% medium with 1.0% acetic acid could inhibit VBNC state formation and kill E. coli O157:H7 within 3 days. The VBNC cell number was reduced by adding 1.0% acetic acid. PMA-PCR assay could be used to detect E. coli VBNC cells in crystal cake with detection limit at 10⁴ CFU/ml. The understanding on the inducing and inhibitory conditions for the VBNC state of E. coli O157:H7 in a typical food system, as well as the development of an efficient VBNC cell detection method might aid in the control of VBNC E. coli O157:H7 cells in the food industry.

Did the ban on serving raw beef liver in restaurants decrease Enterohemorrhagic Escherichia coli infection in Japan?: an interrupted time-series analysis

BACKGROUND

Enterohemorrhagic Escherichia coli (EHEC) is an important pathogen that causes diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). After an EHEC outbreak involving uncooked beef, serving raw beef liver dishes at restaurants was completely banned starting on July 1, 2012 in Japan. However, its long-term associations with the incidence rates of EHEC infections have never been assessed by formal interrupted time-series analysis (ITSA).

METHODS

A retrospective cohort study to assess the impact of banning raw beef liver provision at restaurants was conducted. The weekly incidence of asymptomatic and symptomatic EHEC infections, the incidence of HUS, and deaths were extracted from the national reportable diseases database from January 2008 to December 2017. ITSA was conducted to evaluate the impact of banning raw beef liver from July 2012. To account for a potential simultaneous external effect, the additional regulation on raw beef red meat handling (implemented in May 2011) and the seasonality were also incorporated into the model.

RESULTS

There were 32,179 asymptomatic and 21,250 symptomatic EHEC infections (including 717 HUS cases and 26 deaths) reported during the study period. During the pre-intervention period (before week 27, 2012), there were 0.45 asymptomatic EHEC infections per million-persons per week. The mean post-intervention asymptomatic EHEC infections were 0.51 per million-persons per week. ITSA revealed no baseline trend or change in the intercept and trend (0.002 infections per million-persons per week, 95% Confidence interval - 0.03-0.04, p = 0.93, 1.22, CI -1.96-4.39, p = 0.45, and - 0.006, CI -0.003-0.02, p = 0.68, respectively). For symptomatic EHEC infections, there were 0.30 cases per million per week during the pre-intervention period, and it became 0.33 cases per million per week after the intervention. Time series modeling again did not show a significant baseline trend or changes in the intercept and trend (0.0005, CI -0.02-0.02, p = 0.96, 0.69, CI -1.75-3.12, p = 0.58, and - 0.003, CI -0.02-0.01, p = 0.76, respectively).

CONCLUSION

We did not find a statistically significant reduction in the overall incidence rates of both asymptomatic and symptomatic EHEC infections in Japan after implementing measures, including a ban on serving raw beef liver dishes in the restaurant industry.

Reduction in pathogenic load of wheat by tempering with saline organic acid solutions at different seasonal temperatures

As a raw agricultural commodity, wheat is exposed to microbial contamination; therefore, enteric pathogens may be among its microbiota creating a food safety risk in milled products. This research evaluates (1) the effectiveness of organic acids dissolved in saline solutions to reduce the counts of pathogenic microorganisms in soft and hard wheat, and also investigates the effect of seasonal temperature on (2) survivability of pathogens in wheat kernels and on (3) pathogen inactivation during tempering with saline organic acid solutions. Wheat samples were inoculated with cocktails of either 5 serovars of Salmonella enterica, 5 E. coli O157:H7 or 6 non-O157 Shiga toxin-producing E. coli (STEC) strains to achieve a concentration of ~7 log CFU/g. Inoculated samples were allowed to stand for 7-days at temperatures (2.0, 10.8, 24.2, 32 °C) corresponding to those experienced during winter, spring/fall, and summer (average and maximum) in the main wheat growing regions in the state of Nebraska, USA. Besides water, solutions containing acid (acetic or lactic 2.5% or 5.0% v/v) and NaCl (~26% w/v) were used for tempering the wheat to 15.0% (soft) and 15.5% (hard) moisture at the different seasonal temperatures. The survival of pathogenic microorganisms throughout the resting period, and before and after tempering was analyzed by plating samples on injury-recovery media. The survival rate of pathogenic microorganisms on wheat kernels was higher at temperatures experienced during the winter (2.0 °C) and spring/fall (10.8 °C) months. Regardless of tempering temperature, the initial pathogen load was reduced significantly by all solutions when compared to the control tempered with water (P ≤ .05). The combination of lactic acid (5.0%) and NaCl was the most effective treatment against Salmonella enterica, E. coli O157:H7 and non-O157 STEC, with average reduction values of 1.8, 1.8 and 1.6 log CFU/g for soft wheat and 2.6, 2.4 and 2.4 log CFU/g for hard wheat, respectively. Implementation of organic acids and NaCl in tempering water may have the potential to reduce the risk of pathogen contamination in milled products.

A Multistate Outbreak of E Coli O157:H7 Infections Linked to Soy Nut Butter

BACKGROUND

In 2017, we conducted a multistate investigation to determine the source of an outbreak of Shiga toxin-producing Escherichia coli (STEC) O157:H7 infections, which occurred primarily in children.

METHODS

We defined a case as infection with an outbreak strain of STEC O157:H7 with illness onset between January 1, 2017, and April 30, 2017. Case patients were interviewed to identify common exposures. Traceback and facility investigations were conducted; food samples were tested for STEC.

RESULTS

We identified 32 cases from 12 states. Twenty-six (81%) cases occurred in children <18 years old; 8 children developed hemolytic uremic syndrome. Twenty-five (78%) case patients ate the same brand of soy nut butter or attended facilities that served it. We identified 3 illness subclusters, including a child care center where person-to-person transmission may have occurred. Testing isolated an outbreak strain from 11 soy nut butter samples. Investigations identified violations of good manufacturing practices at the soy nut butter manufacturing facility with opportunities for product contamination, although the specific route of contamination was undetermined.

CONCLUSIONS

This investigation identified soy nut butter as the source of a multistate outbreak of STEC infections affecting mainly children. The ensuing recall of all soy nut butter products the facility manufactured, totaling >1.2 million lb, likely prevented additional illnesses. Prompt diagnosis of STEC infections and appropriate specimen collection aids in outbreak detection. Child care providers should follow appropriate hygiene practices to prevent secondary spread of enteric illness in child care settings. Firms should manufacture ready-to-eat foods in a manner that minimizes the risk of contamination.

Whole Genome Sequencing Characterization of Shiga Toxin-Producing Escherichia coli Isolated from Flour from Swiss Retail Markets

Shiga toxin-producing Escherichia coli (STEC) strains are often found in food and cause human infections. Although STEC O157:H7 is most often responsible for human disease, various non-O157 subtypes have caused individual human infections or outbreaks. The importance of STEC serogroup typing is decreasing while detection of virulence gene patterns has become more relevant. Whole genome sequencing (WGS) reveals the entire spectrum of pathogen information, such as toxin variant, serotype, sequence type, and virulence factors. Flour has not been considered as a vector for STEC; however, this product has been associated with several STEC outbreaks in the last decade. Flour is a natural product, and milling does not include a germ-reducing step. Flour is rarely eaten raw, but the risks associated with the consumption of unbaked dough are probably underestimated. The aim of this study was to determine the prevalence of STEC in flour samples (n = 93) collected from Swiss markets and to fully characterize the isolates by PCR assay and WGS. The prevalence of STEC in these flour samples was 10.8% as indicated by PCR, and a total of 10 STEC strains were isolated (two flour samples were positive for two STEC subtypes). We found one stx₂-positve STEC isolate belonging to the classic serogroups frequently associated with outbreaks that could potentially cause severe disease. However, we also found several other common or less common STEC subtypes with diverse virulence patterns. Our results reveal the benefits of WGS as a characterization tool and that flour is a potentially and probably underestimated source for STEC infections in humans.

Encapsulation of E. coli phage ZCEC5 in chitosan-alginate beads as a delivery system in phage therapy

Bacteriophages can be used successfully to treat pathogenic bacteria in the food chain including zoonotic pathogens that colonize the intestines of farm animals. However, harsh gastric conditions of low pH and digestive enzyme activities affect phage viability, and accordingly reduce their effectiveness. We report the development of a natural protective barrier suitable for oral administration to farm animals that confers acid stability before functional release of bead-encapsulated phages. Escherichia coli bacteriophage ZSEC5 is rendered inactive at pH 2.0 but encapsulation in chitosan–alginate bead with a honey and gelatin matrix limited titer reductions to 1 log₁₀ PFU mL⁻¹. The encapsulated phage titers were stable upon storage in water but achieved near complete release over 4–5 h in a simulated intestinal solution (0.1% bile salt, 0.4% pancreatin, 50 mM KH₂PO₄ pH 7.5) at 37 °C. Exposure of E. coli O157:H7 to the bead-encapsulated phage preparations produced a delayed response, reaching a maximal reductions of 4.2 to 4.8 log₁₀ CFU mL⁻¹ after 10 h at 37 °C under simulated intestinal conditions compared to a maximal reduction of 5.1 log₁₀ CFU mL⁻¹ at 3 h for free phage applied at MOI = 1. Bead-encapsulation is a promising reliable and cost-effective method for the functional delivery of bacteriophage targeting intestinal bacteria of farm animals.

Occurrence and Levels of Salmonella, Enterohemorrhagic Escherichia coli, and Listeria in Raw Wheat

HIGHLIGHTS

Prevalence of Salmonella and E. coli in raw wheat emphasizes the need to cook wheat products. 3,891 grain samples were tested for E. coli and Salmonella; 1,285 were tested for Listeria. Of wheat berries sampled, 0.44% were positive for E. coli and 1.23% were positive for Salmonella. Salmonella diversity was high, indicating various animal sources that are difficult to prevent. Cooking wheat products is the best preventative measure against foodborne illness from wheat.

Growth of Salmonella and Other Foodborne Pathogens on Inoculated Inshell Pistachios during Simulated Delays between Hulling and Drying

During harvest, pistachios are hulled, separated in water into floater and sinker streams (in large part on the basis of nut density), and then dried before storage. Higher prevalence and levels of Salmonella were previously observed in floater pistachios, but contributing factors are unclear. To examine the behavior of pathogens on hulled pistachios during simulated drying delays, floater and sinker pistachios collected from commercial processors were inoculated at 1 or 3 log CFU/g with cocktails of Salmonella and in some cases Escherichia coli O157:H7 or Listeria monocytogenes and incubated for up to 30 h at 37°C and 90% relative humidity. Populations were measured by plating onto tryptic soy agar and appropriate selective agars. In most cases, no significant growth (P > 0.05) of Salmonella was observed in the first 3 h after inoculation in hulled floaters and sinkers. Growth of Salmonella was greater on floater pistachios than on corresponding sinkers and on floater pistachios with ≥25% hull adhering to the shell surface than on corresponding floaters with <25% adhering hull. Maximum Salmonella populations (2 to 7 log CFU/g) were ∼2-log higher on floaters than on corresponding sinkers. The growth of E. coli O157:H7 and Salmonella on hulled pistachios was similar, but a longer lag time (approximately 11 h) and significantly lower maximum populations (4 versus 5 to 6 log CFU/g; P < 0.05) were predicted for L. monocytogenes. Significant growth of pathogens on hulled pistachios is possible when delays between hulling and drying are longer than 3 h, and pathogen growth is enhanced in the presence of adhering hull material.

Laboratory Review of Foodborne Disease Investigations in Washington State 2007-2017

The Washington State Department of Health Public Health Laboratories (WAPHL) has tested 11,501 samples between 2007 and 2017 for a foodborne disease using a combination of identification, serotyping, and subtyping tools. During this period there were 8037 total clinical and environmental samples tested by pulsed-field gel electrophoresis (PFGE), including 512 foodborne disease clusters and 2176 PFGE patterns of Salmonella enterica subsp. enterica. There were 2446 Shiga toxin–producing Escherichia coli samples tested by PFGE, which included 158 foodborne disease clusters and 1174 PFGE patterns. There were 332 samples of Listeria monocytogenes tested by PFGE, including 35 foodborne disease clusters and 104 PFGE patterns. Sources linked to outbreaks included raw chicken, unpasteurized dairy products, various produce types, and undercooked beef among others. As next-generation sequencing (NGS) replaces PFGE, the impact of this transition is expected to be significant given the enhanced cluster detection power NGS brings. The measures presented here will be a reference baseline in future years.

Modeling the Risk of Salmonellosis from Consumption of Peanuts in the United States

Peanut products were the target of the largest food recall in United States history from 2008 to 2009, with more than 3,200 products implicated, economic losses estimated at $1 billion, and more than 700 reported illnesses and 9 deaths. Predictive modeling tools such as quantitative microbial risk assessment can be used to aid processors in making risk management decisions that may reduce the chances of foodborne illness, but published risk assessment for peanuts is not currently available. A quantitative microbial risk assessment was performed to quantify salmonellosis risk from consumption of peanuts in the United States. Prevalence and concentration data for Salmonella on raw, shelled peanuts were used in combination with probability distributions of simulated log reductions achieved during production steps before consumption. Data for time-temperature combinations used in each step were obtained from published literature, industry surveys, or expert opinion, and survival data were obtained from the literature. A beta-Poisson dose-response model was used to predict probability of illness from ingestion of Salmonella cells. The model predicted 14.2 (arithmetic mean) or 0.0123 (geometric mean) illnesses per year. Sensitivity analysis showed that thermal inactivation log reductions applied had the biggest impact on predicted salmonellosis risk, followed by consumer storage time, Salmonella starting concentration, Salmonella starting prevalence, and number of originally contaminated 25-g servings per originally positive 375-g sample. Scenario analysis showed that increasing log reduction variability increased mean salmonellosis risk. Removing the effect of storage on Salmonella survival increased the arithmetic and geometric means to 153 and 0.598 illnesses per year, respectively. This study indicated that the risk of salmonellosis from consumption of peanuts can be lowered by reducing field contamination, control of storage steps, and monitoring of appropriate critical limits in peanut roasting.

Salmonella and Enterohemorrhagic Escherichia coli Serogroups O45, O121, O145 in Wheat Flour: Effects of Long-Term Storage and Thermal Treatments

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.

Detection, Isolation, and Characterization of Shiga Toxin-Producing Escherichia coli in Flour

Wheat flour has recently been described as a novel vehicle for transmission of Shiga toxin-producing Escherichia coli (STEC). Very recently, an outbreak of STEC O121 and STEC O26 infections was linked to flour in the United States. The aim of the present study was to generate baseline data for the occurrence of STEC in flour samples from different retailers in Switzerland. In total, 70 flour samples were analyzed. After enrichment, the samples were screened for stx₁ and stx₂ by the Assurance GDS MPX ID assay. STEC strains were isolated and serotyped by the E. coli SeroGenoTyping AS-1 kit. The determination of stx subtypes was performed with conventional PCR amplification. Screening for eae, aggR, elt, and estIa/Ib was performed by real-time PCR. Nine (12.9%) of the flour samples tested positive for stx by PCR. STEC was recovered from eight (88.9%) of the positive samples. Two isolates were STEC O11:H48 harboring stx_1c/ stx_1d, two were O146:H28 containing stx_2b, one was O103:H2 containing stx_1a and eae, and three were O nontypeable: Ont:H12 ( stx_2a), Ont:H14 ( stx_2a/ stx_2g), and Ont:H31 ( stx_1c/ stx_1d). STEC O103 belongs to the "top five" serogroups of human pathogenic STEC in the European Union, and STEC O146 is frequently isolated from diseased humans in Switzerland. Our results show that flour may be contaminated with a variety of STEC serogroups. Consumption of raw or undercooked flour may constitute a risk for STEC infection.

Long-Term Survival and Thermal Death Kinetics of Enterohemorrhagic Escherichia coli Serogroups O26, O103, O111, and O157 in Wheat Flour

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.

Web survey-based selection of controls for epidemiological analyses of a multi-prefectural outbreak of enterohaemorrhagic Escherichia coli O157 in Japan associated with consumption of self-grilled beef hanging tender

An outbreak of enterohaemorrhagic Escherichia coli O157 occurred in multiple prefectures of Japan in November 2009. We conducted two case-control studies with trace-back and trace-forward investigations to determine the source. The case definition was met by 21 individuals; 14 (66.7%) were hospitalised, but no haemolytic uraemic syndrome, acute encephalopathy or deaths occurred. Median age was 23 (range 12-48) years and 14 cases were male (66.7%). No significant associations with food were found in a case-control study by local public health centres, but our matched case-control study using Internet surveys found that beef hanging tender (or hanger steak), derived from the diaphragm of the cattle, was significantly associated with illness (odds ratio = 15.77; 95% confidence interval, 2.00-124.11). Pulsed-field gel electrophoresis analysis of isolates from patients and the suspected food showed five different patterns: two in faecal and food samples, and another three in patient faecal samples only, although there were epidemiological links to the meat consumed at the restaurants. Trace-back investigation implicated a common food processing company from outside Japan. Examination of the logistics of the meat processing company suggested that contamination did not occur in Japan. We concluded that the source of the outbreak was imported hanging tender. This investigation revealed that Internet surveys could be useful for outbreak investigations.

Shiga Toxin-Producing E. coli Infections Associated with Flour

BACKGROUND

In 2016, a multijurisdictional team investigated an outbreak of Shiga toxin-producing Escherichia coli (STEC) serogroup O121 and O26 infections linked to contaminated flour from a large domestic producer.

METHODS

A case was defined as infection with an outbreak strain in which illness onset was between December 21, 2015, and September 5, 2016. To identify exposures associated with the outbreak, outbreak cases were compared with non-STEC enteric illness cases, matched according to age group, sex, and state of residence. Products suspected to be related to the outbreak were collected for STEC testing, and a common point of contamination was sought. Whole-genome sequencing was performed on isolates from clinical and food samples.

RESULTS

A total of 56 cases were identified in 24 states. Univariable exact conditional logistic-regression models of 22 matched sets showed that infection was significantly associated with the use of one brand of flour (odds ratio, 21.04; 95% confidence interval [CI], 4.69 to 94.37) and with tasting unbaked homemade dough or batter (odds ratio, 36.02; 95% CI, 4.63 to 280.17). Laboratory testing isolated the outbreak strains from flour samples, and whole-genome sequencing revealed that the isolates from clinical and food samples were closely related to one another genetically. Trace-back investigation identified a common flour-production facility.

CONCLUSIONS

This investigation implicated raw flour as the source of an outbreak of STEC infections. Although it is a low-moisture food, raw flour can be a vehicle for foodborne pathogens.