Generic Escherichia coli contamination of spinach at the preharvest stage: effects of farm management and environmental factors

Factors Associated with the Prevalence of Salmonella, Generic Escherichia coli, and Coliforms in Florida's Agricultural Soils

Limited data exist on the environmental factors that impact pathogen prevalence in the soil. The prevalence of foodborne pathogens, Salmonella and Listeria monocytogenes, and the prevalence and concentration of generic E. coli in Florida's agricultural soils were evaluated to understand the potential risk of microbial contamination at the preharvest level. For all organisms but L. monocytogenes, a longitudinal field study was performed in three geographically distributed agricultural areas across Florida. At each location, 20 unique 5 by 5 m field sampling sites were selected, and soil was collected and evaluated for Salmonella presence (25 g) and E. coli and coliform concentrations (5 g). Complementary data collected from October 2021 to April 2022 included: weather; adjacent land use; soil properties, including macro- and micro-nutrients; and field management practices. The overall Salmonella and generic E. coli prevalence was 0.418% (1/239) and 11.3% (27/239), respectively; with mean E. coli concentrations in positive samples of 1.56 log CFU/g. Farm A had the highest prevalence of generic E. coli, 22.8% (18/79); followed by Farm B, 10% (8/80); and Farm C 1.25% (1/80). A significant relationship (p < 0.05) was observed between generic E. coli and coliforms, and farm and sampling trip. Variation in the prevalence of generic E. coli and changes in coliform concentrations between farms suggest environmental factors (e.g. soil properties) at the three farms were different. While Salmonella was only detected once, generic E. coli was detected in Florida soils throughout the duration of the growing season meaning activities that limit contact between soil and horticultural crops should continue to be emphasized. Samples collected during an independent sampling trip were evaluated for L. monocytogenes, which was not detected. The influence of local environmental factors on the prevalence of indicator organisms in the soil presents a unique challenge when evaluating the applicability of more global models to predict pathogen prevalence in preharvest produce environments.

Modeling Growth Kinetics of Escherichia coli and Background Microflora in Hydroponically Grown Lettuce

Hydroponic cultivation of lettuce is an increasingly popular sustainable agricultural technique. However, Escherichia coli, a prevalent bacterium, poses significant concerns for the quality and safety of hydroponically grown lettuce. This study aimed to develop a growth model for E. coli and background microflora in hydroponically grown lettuce. The experiment involved inoculating hydroponically grown lettuce with E. coli and incubated at 4, 10, 15, 25, 30, 36 °C. Growth models for E. coli and background microflora were then developed using Origin 2022 (9.9) and IPMP 2013 software and validated at 5 °C and 20 °C by calculating root mean square errors (RMSEs). The result showed that E. coli was unable to grow at 4 °C and the SGompertz model was determined as the most appropriate primary model. From this primary model, the Ratkowsky square root model and polynomial model were derived as secondary models for E. coli-R168 and background microflora, respectively. These secondary models determined that the minimum temperature (Tmin) required for the growth of E. coli and background microflora in hydroponically grown lettuce was 6.1 °C and 8.7 °C, respectively. Moreover, the RMSE values ranged from 0.11 to 0.24 CFU/g, indicating that the models and their associated kinetic parameters accurately represented the proliferation of E. coli and background microflora in hydroponically grown lettuce.

Internalization of Salmonella in Leafy Vegetables during Postharvest Conditions

The consumption of fresh produce is increasing due to its role in promoting a healthy and balanced diet. However, this trend is accompanied by increased foodborne disease cases associated with pathogens such as Escherichia, Listeria, and Salmonella. Previous studies provided evidence that the internalization of foodborne pathogens in fresh produce may be a potential contamination route and may pose a public health risk. This study investigates the combination effects of storage temperature and humidity on Salmonella internalization in six types of leafy greens (iceberg lettuce, romaine lettuce, red lettuce, green onion, spinach, and kale) during the storage stage. The results indicated that temperature plays a critical role in Salmonella internalization, with higher concentrations observed in samples stored at 25 °C compared to those stored at 7 °C. The mean concentration of internalized Salmonella in the iceberg lettuce sample was the highest and that in the green onion sample was the lowest (iceberg lettuce > red lettuce > romaine lettuce > spinach > kale > green onion). Mist conditions also had an impact on internalization. The group treated with mist showed an increase in Salmonella internalization of about 10-30% rather than the group without mist treatment. This research emphasizes the importance of understanding the factors influencing bacterial internalization in fresh produce and highlights the need for proper storage conditions to minimize the risk of contamination and ensure food safety.

What on earth? The impact of digestates and composts from farm effluent management on fluxes of foodborne pathogens in agricultural lands

The recycling of biomass is the cornerstone of sustainable development in the bioeconomy. In this context, digestates and composts from processed agricultural residues and biomasses are returned to the soil. Whether or not the presence of pathogenic microorganisms in these processed biomasses is a threat to the sustainability of the current on-farm practices is still the subject of debate. In this review, we describe the microbial pathogens that may be present in digestates and composts. We then provide an overview of the current European regulation designed to mitigate health hazards linked to the use of organic fertilisers and soil improvers produced from farm biomasses and residues. Finally, we discuss the many factors that underlie the fate of microbial pathogens in the field. We argue that incorporating land characteristics in the management of safety issues connected with the spreading of organic fertilisers and soil improvers can improve the sustainability of biomass recycling.

The effectiveness of treating irrigation water using ultraviolet radiation or sulphuric acid fertilizer for reducing generic Escherichia coli on fresh produce-a controlled intervention trial

AIMS

The aims of this study were to: (i) estimate the effectiveness of ultraviolet radiation (UV) and sulphuric acid-based fertilizer (SA), at reducing levels of generic Escherichia coli in surface irrigation water and on produce and surface soil in open produce fields; and (ii) describe the population dynamics of generic E. coli in produce fields.

METHODS AND RESULTS

Spinach and cantaloupe plots were randomly assigned to control, UV or SA treatment groups. Irrigation water was inoculated with Rifampicin-resistant E. coli prior to treatment. More than 75% of UV- and SA-treated tank water samples had counts below the detection limit, compared to a mean count of 3·3 Log10 CFU per ml before treatment. Levels of Rifampicin-resistant E. coli in soil and produce both increased and decreased over 10-15 days after irrigation, depending on the plot and time-period.

CONCLUSIONS

UV and SA treatments effectively reduce the levels of E. coli in surface irrigation water. Their effectiveness at reducing contamination on produce was dependent on environmental conditions. Applying wait-times after irrigation and prior to harvest is not a reliable means of mitigating against contaminated produce.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results are of timely importance for the agricultural industry as new FSMA guidelines require producers to demonstrate a low microbial load in irrigation water or allow producers to apply a wait-time to mitigate the risk of contaminated produce.

Airborne Dissemination of Bacteria (Enterococci, Staphylococci and Enterobacteriaceae) in a Modern Broiler Farm and Its Environment

Simple Summary

In this study, the density and diversity of relevant groups of bacteria at a broiler farm have been studied, in the inside and outside air and in litter samples. A high number of bacteria was detected in the litter and in the inside air, but a low emission of bacteria was found in the outside air. Moreover, the bacteria detected in the outside air decreased with the distance to the farm. A total of 544 isolates were identified from all the samples (146 from the litter, 142 from inside air and 256 from outside air). From these, 162 staphylococci, 176 Enterobacteriaceae, and 190 enterococci were detected. E. hirae was the predominant species and the detection of identical DNA profiles in E. hirae isolates from inside and outside samples suggests the role of the air in bacterial dissemination from the inside of the broiler farm to the immediate environment. It is necessary to consider the relevance of air as a vehicle of disseminating bacteria at the farm level, which can involve potentially pathogenic bacteria and bacteria carrying antimicrobial resistance genes.

Abstract

The role of the air as a vehicle of bacteria dissemination in the farming environment has been previously reported, but still scarcely studied. This study investigated the bacteria density/diversity of the inside and outside air and of litter samples at a broiler farm. Samples were collected considering two seasons, three outside air distances (50/100/150 m) and the four cardinal directions. Selective media was used for staphylococci, enterococci, and Enterobacteriaceae recovery. A high number of bacteria was detected in the litter (2.9 × 10⁵–5.8 × 10⁷ cfu/g) and in the inside air (>10⁵ cfu/m³), but a low emission of bacteria was evidenced in the outside air (<6 cfu/m³). Moreover, the bacteria detected in the farm’s outside air decreased the further from the farm the sample was taken. A total of 544 isolates were identified by MALDI-TOF (146 from the litter, 142 from inside air and 256 from outside air). From these, 162 staphylococci (14 species; S. saprophyticus 40.7%), 176 Enterobacteriaceae (4 species; E. coli 66%) and 190 enterococci (4 species; E. hirae 83%) were detected. E. hirae was the predominant species, and identical PFGE clones were detected in inside and outside samples. The detection of identical DNA profiles in E. hirae isolates from inside and outside samples suggests the role of the air in bacterial dissemination from the inside of the broiler farm to the immediate environment.

Detection of Toxoplasma gondii oocysts on organic and conventionally grown produce

Toxoplasma gondii infection can result in toxoplasmosis and potential psychological effects. Research commonly focuses on infection through contact with cat fecal matter or consumption of contaminated meat. However, T. gondii oocysts can persist in the environment for years and may be present in soils and on soil-grown produce. Rates of oocyst DNA recovery from produce were high, with 18% of vegetable samples testing positive for T. gondii via PCR test and melt curve analysis. Radishes had significantly higher oocyst counts than arugula, collard greens, kale, lettuce, and spinach. There were no significant differences in oocyst detection rates between samples taken from organic farmer's markets and conventional grocery stores. This study demonstrates that these oocysts can transfer to produce grown both conventionally and using organic techniques.

Salmonella, Food Safety and Food Handling Practices

Salmonellosis is the second most reported gastrointestinal disorder in the EU resulting from the consumption of Salmonella-contaminated foods. Symptoms include gastroenteritis, abdominal cramps, bloody diarrhoea, fever, myalgia, headache, nausea and vomiting. In 2018, Salmonella accounted for more than half of the numbers of foodborne outbreak illnesses reported in the EU. Salmonella contamination is mostly associated with produce such as poultry, cattle and their feeds but other products such as dried foods, infant formula, fruit and vegetable products and pets have become important. Efforts aimed at controlling Salmonella are being made. For example, legislation and measures put in place reduced the number of hospitalizations between 2014 and 2015. However, the number of hospitalizations started to increase in 2016. This calls for more stringent controls at the level of government and the private sector. Food handlers of "meat processing" and "Ready to Eat" foods play a crucial role in the spread of Salmonella. This review presents an updated overview of the global epidemiology, the relevance of official control, the disease associated with food handlers and the importance of food safety concerning salmonellosis.

The under-investigated wild side of Escherichia coli: genetic diversity, pathogenicity and antimicrobial resistance in wild animals

A striking paucity of information exists on Escherichia coli in wild animals despite evidence that they harbour pathogenic and antimicrobial-resistant E. coli in their gut microbiomes and may even serve as melting pots for novel genetic combinations potentially harmful to human health. Wild animals have been implicated as the source of pathogenic E. coli outbreaks in agricultural production, but a lack of knowledge surrounding the genetics of E. coli in wild animals complicates source tracking and thus contamination curtailment efforts. As human populations continue to expand and invade wild areas, the potential for harmful microorganisms to transfer between humans and wildlife increases. Here, we conducted a literature review of the small body of work on E. coli in wild animals. We highlight the geographic and host taxonomic coverage to date, and in each, identify significant gaps. We summarize the current understanding of E. coli in wild animals, including its genetic diversity, host and geographic distribution, and transmission pathways within and between wild animal and human populations. The knowledge gaps we identify call for greater research efforts to understand the existence of E. coli in wild animals, especially in light of the potentially strong implications for global public health.

Microbial and physicochemical assessment of irrigation water treatment methods

AIMS

The presence of foodborne pathogens in preharvest agricultural water has been identified as a potential contamination source in outbreak investigations, driving markets and auditing bodies to begin requiring water treatment for high-risk produce. Therefore, it is essential that we identify water treatment methods which are effective as well as practical in their application on farm.

METHODS AND RESULTS

In this work, we evaluated two sanitizers which are most prominent in preharvest agricultural water treatment (calcium hypochlorite (free chlorine: 3-5 ppm) and peracetic acid (PAA: 5 ppm)), an EPA registered antimicrobial device (ultraviolet light (UV)), in addition to a combination approach (chlorine + UV, PAA + UV). Treatments were evaluated for their ability to inactivate total coliforms and generic Escherichia coli and consistency in treatment efficacy over 1 h of operation. Physicochemical variables were measured along with microbial populations at 0, 5, 15, 30, 45 and 60 min of operation. Escherichia coli and coliform counts showed a significant (P < 0·05) reduction after treatment, with combination and singular treatments equally effective at inactivating E. coli and coliforms. A significant increase (P < 0·05) in oxidation-reduction potential was seen during water treatment (Chlorine; UV + Chlorine), and a significant reduction (P < 0·05) in pH was seen after PAA and PAA + UV treatments (60 min).

CONCLUSION

Overall, the results indicate that all treatments evaluated are equally efficacious for inactivating E. coli and coliforms present in surface agricultural water.

SIGNIFICANCE AND IMPACT OF THE STUDY

This information when paired with challenge studies targeting foodborne pathogens of interest can be used to support grower decisions when selecting and validating a preharvest agricultural water treatment programme.

Antimicrobial resistance and genomic characterisation of Escherichia coli isolated from caged and non-caged retail table eggs in Western Australia

Foodborne exposure to antimicrobial-resistant bacteria is a growing global health concern. Escherichia coli (E. coli) is well recognised as an indicator of food contamination with faecal materials. In the present study, we investigated the occurrence of E. coli in table eggs sold at retail supermarkets in Western Australia (WA). A total of 2172 visually clean and intact retail eggs were purchased between October 2017 and June 2018. A single carton containing a dozen eggs was considered as a single sample resulting a total of 181 samples. The shells and contents of each sample were separately pooled and tested using standard culture-based methods. Overall, generic E. coli was detected in 36 (19.8%; 95% confidence interval: 14.3; 26.4) of the 181 tested retail egg samples. We characterised 100 of the recovered E. coli isolates for their phenotypic antimicrobial resistance using minimum inhibitory concentration (MIC). A subset of E. coli isolates (n = 14) were selected on the basis of their MIC patterns, and were further characterised using whole genome sequencing (WGS). Fifty-seven (57%) of the recovered generic E. coli isolates (n = 100) were resistant to at least one of the 14 antimicrobials included in the MIC testing panel, of which 22 isolates (22%) showed multi-class resistance. The highest frequencies of non-susceptibility of E. coli isolated from WA retailed eggs were against tetracycline (49%) and ampicillin (36%). WGS revealed that tet(A) and bla_TEM-1B genes were present in most of the isolates exhibiting phenotypic resistance to tetracycline and ampicillin, respectively. The majority (98%) of the characterised E. coli isolates were susceptible to ciprofloxacin and azithromycin, and none were resistant to the cephalosporin antimicrobials included in the MIC panel. Two isolates demonstrated reduced susceptibility to ciprofloxacin, with MICs of 0.125 and 0.25 mg/L, and WGS revealed the presence of plasmid mediated qnrs1 gene in both isolates. This is the first report on detection of non-wild-type resistance to fluoroquinolones in supermarket eggs in Australia; one of the two isolates was from a cage-laid eggs sample while the other was from a barn-laid retail eggs sample. Fluoroquinolones have never been permitted for use in poultry farms in Australia. Thus, the detection of low-level ciprofloxacin-resistant E. coli in the absence of local antimicrobial selection pressure at the Australian layer farms warrants further research on the potential role of the environment or human-related factors in the transmission of antimicrobial resistance. The results of this study add to the local and global understanding of antimicrobial resistance spread in foods of animal origin.

Listeria monocytogenes Prevalence Varies More within Fields Than between Fields or over Time on Conventionally Farmed New York Produce Fields

ABSTRACT

Past studies have shown that the on-farm distribution of Listeria monocytogenes is affected by environmental factors (e.g., weather). However, most studies were conducted at large scales (e.g., across farms), whereas few studies examined drivers of L. monocytogenes prevalence at smaller scales (e.g., within a single field). This study was performed to address this knowledge gap by (i) tracking L. monocytogenes distribution in two fields on one farm over a growing season and (ii) identifying factors associated with L. monocytogenes isolation from drag swab, soil, and agricultural water samples. Overall, L. monocytogenes was detected in 78% (21 of 27), 19% (7 of 36), and 8% (37 of 486) of water, drag swab, and soil samples, respectively. All isolates were characterized by pulsed-field gel electrophoresis. Of the 43 types identified, 14 were isolated on multiple sampling visits and/or from multiple sample types, indicating persistence in or repeated introduction into the farm environment during the study. Our findings also suggest that L. monocytogenes prevalence, even at the small spatial scale studied here, (i) was not uniform and (ii) varied more within fields than between fields or over time. This is illustrated by plot (in-field variation), field (between-field variation), and sampling visit (time), accounting for 18, 2, and 3% of variance in odds of isolating L. monocytogenes, respectively. Moreover, according to random forest analysis, water-related factors were among the top-ranked factors associated with L. monocytogenes isolation from all sample types. For example, the likelihood of isolating L. monocytogenes from drag and soil samples increased monotonically as rainfall increased. Overall, findings from this single-farm study suggests that mitigation strategies for L. monocytogenes in produce fields should focus on water-associated risk factors (e.g., rain and distance to water) and be tailored to specific high-risk in-field areas.

HIGHLIGHTS

Total Coliform and Generic E. coli Levels, and Salmonella Presence in Eight Experimental Aquaponics and Hydroponics Systems: A Brief Report Highlighting Exploratory Data

Although many studies have investigated foodborne pathogen prevalence in conventional produce production environments, relatively few have investigated prevalence in aquaponics and hydroponics systems. This study sought to address this knowledge gap by enumerating total coliform and generic E. coli levels, and testing for Salmonella presence in circulating water samples collected from five hydroponic systems and three aquaponic systems (No. of samples = 79). While total coliform levels ranged between 6.3 Most Probable Number (MPN)/100-mL and the upper limit of detection (2496 MPN/100-mL), only three samples had detectable levels of E. coli and no samples had detectable levels of Salmonella. Of the three E. coli positive samples, two samples had just one MPN of E. coli/100-mL while the third had 53.9 MPN of E. coli/100-mL. While the sample size reported here was small and site selection was not randomized, this study adds key data on the microbial quality of aquaponics and hydroponics systems to the literature. Moreover, these data suggest that contamination in these systems occurs at relatively low-levels, and that future studies are needed to more fully explore when and how microbial contamination of aquaponics and hydroponic systems is likely to occur.

Applying Quantitative Microbial Risk Assessment Model in Developing Appropriate Standards for Irrigation Water

This study aimed to apply a quantitative microbial risk assessment (QMRA) model to estimate the annual risk probability of Salmonella infection associated with the consumption of crops, which were irrigated with raw wastewater abstracted by farmers without official permission. Data generated from the model were used to propose realistic standards for Salmonella in irrigation water needed for safe crop production. Results demonstrated the presence of total coliforms, fecal coliforms, fecal streptococci, and Salmonella in wastewater samples. Salmonella was recorded on lettuce and spinach in 3 different harvesting events, although it was not found in data obtained for parsley plant. The QMRA scenario included surface irrigation, consumption of raw crops, and 1-day withholding period before harvest. The annual risk probability of Salmonella infection for consumers exceeded the target tolerable risk (7.7 × 10-4 ) for investigated crops. The Pearson's correlation coefficient between different annual risk probabilities showed significant correlation (p < 0.05). The levels of risk posed from spinach and lettuce were roughly similar, although they tended to be higher for lettuce. The optimum concentrations of Salmonella in irrigation water needed to satisfy the World Health Organization guidelines of disease burden (disability-adjusted life years 10-6 ) per person per year ranged from 34 to 119 via multiple-tube fermentation technique/100 mL, for spinach and lettuce plants, respectively. The study concluded that unofficial reuse of wastewater in irrigation is a principle route for crop contamination. Water quality monitoring programs should be integrated with QMRA investigations for better estimation of risk level. The fit parameters used could be tailored to cover a wide array of local situations in different countries. Models applied for viruses, helminths, and bacteria other than Salmonella are encouraged in future studies. Integr Environ Assess Manag 2020;16:353-361. © 2019 SETAC.

Growth and Survival of Listeria monocytogenes on Intact Fruit and Vegetable Surfaces during Postharvest Handling: A Systematic Literature Review

Listeria monocytogenes may be present in produce-associated environments (e.g., fields, packing houses); thus, understanding its growth and survival on intact, whole produce is of critical importance. The goal of this study was to identify and characterize published data on the growth and/or survival of L. monocytogenes on intact fruit and vegetable surfaces. Relevant studies were identified by searching seven electronic databases: AGRICOLA, CAB Abstracts, Center for Produce Safety funded research project final reports, FST Abstracts, Google Scholar, PubMed, and Web of Science. Searches were conducted using the following terms: Listeria monocytogenes, produce, growth, and survival. Search terms were also modified and "exploded" to find all related subheadings. Included studies had to be prospective, describe methodology (e.g., inoculation method), outline experimental parameters, and provide quantitative growth and/or survival data. Studies were not included if methods were unclear or inappropriate, or if produce was cut, processed, or otherwise treated. Of 3,459 identified citations, 88 were reviewed in full and 29 studies met the inclusion criteria. Included studies represented 21 commodities, with the majority of studies focusing on melons, leafy greens, berries, or sprouts. Synthesis of the reviewed studies suggests L. monocytogenes growth and survival on intact produce surfaces differ substantially by commodity. Parameters such as temperature and produce surface characteristics had a considerable effect on L. monocytogenes growth and survival dynamics. This review provides an inventory of the current data on L. monocytogenes growth and/or survival on intact produce surfaces. Identification of which intact produce commodities support L. monocytogenes growth and/or survival at various conditions observed along the supply chain will assist the industry in managing L. monocytogenes contamination risk.

Quantitative PCR-based identification of enteric viruses contaminating fresh produce and surface water used for irrigation in Egypt

Fresh produce irrigated with surface water that may contain pathogens such as enteric viruses can lead to outbreaks of foodborne viral illnesses. In the current study, we performed real-time PCR (qPCR) to monitor the presence of enteric viruses such as human adenoviruses (HAdVs), hepatitis A virus (HAV), rotavirus group A (RVA), and norovirus GI (NoV GI) in surface water and fresh produce that were grown using this surface water in Egypt. Samples were collected on four occasions from different sites located in the Delta and in Greater Cairo, Egypt. Of the 32 water samples and 128 fresh produce samples, 27/32 (84.3%) and 99/128 (77.3%), respectively, were positive for at least one virus. HAdV (30/32) with a mean viral load = 1.5 × 10⁷ genome copies/L (GC/L) was the most commonly detected virus in water, followed by RVA (16/32, with a mean viral load = 2.7 × 10⁵ GC/L), HAV (11/32, with a mean viral load = 1.2 × 10⁴ GC /L), and NoV GI (10/32, with a mean viral load = 3.5 × 10³ GC/L). Additionally, HAdV (71/128, with a mean viral load = 9.8 × 10⁵ GC/g) was also the most commonly detected virus in the fresh produce, followed by NoV GI (43/128, with a mean viral load = 4.5 × 10³ GC/g), HAV (33/128, with a mean viral load = 6.4 × 10³ GC/g), and RVA (25/128, with a mean viral load = 1.5 × 10⁴ GC/g). Our results indicate that fresh produce may be contaminated with a wide range of enteric viruses, and these viruses may originate from virus-contaminated irrigation water. Moreover, this fresh produce may serve as a potential vector for the transmission of viral foodborne illnesses. These findings are important for future risk assessment analysis related to water/foodborne viruses. Graphical abstract . Please provide caption for Graphical AbstractGraphical abstract showing sample collection and processing.

Overview of Leafy Greens-Related Food Safety Incidents with a California Link: 1996 to 2016

An increase in the number of foodborne illness outbreaks associated with produce has been noted in the literature, and leafy greens have been the most common produce category associated with these outbreaks. California is the largest leafy greens producer in the United States, and many related foodborne illness incidents were traced to this state. A systematic overview of leafy greens incidents linked to California was conducted by the California Department of Public Health, Food and Drug Branch through analysis of complaints, routine surveillance sampling, disease outbreaks, and investigations covering 1996 to 2016. The goal was to develop a risk assessment tool to modernize emergency response efforts to foodborne illnesses related to leafy greens. A database including environmental, epidemiologic, and laboratory information for each incident was developed, and descriptive analysis was performed to identify trends. In the 21-year period analyzed, 134 incidents were identified, the majority of which were surveillance related. Approximately 2,240 U.S. cases of confirmed illness were reported (298 California cases resulting in 50 hospitalizations). Romaine lettuce and spinach were the most commonly implicated vehicles. The most prevalent hazard type was microbiological, in particular bacterial, specifically associated with pathogenic strains of Escherichia coli. In California, the overview provided the Food and Drug Branch with a platform to (i) enhance its Food Safety Program, Emergency Response Unit, and California Food Emergency Response Team; (ii) assist in more efficient investigation, response, control, and prevention of California-linked foodborne illness incidents; and (iii) identify knowledge gaps and develop effective definitions, procedures, training, guidelines, and policies that will be used to help prevent future outbreaks. Outcomes provide insight into the situation in the largest leafy greens-producing state and may be used to prioritize limited national food safety resources and aid in future leafy greens-related research and foodborne incident investigations.

Identification of Enterococci, Staphylococci, and Enterobacteriaceae from Slurries and Air in and around Two Pork Farms

In this study, we investigated the airborne dissemination of bacteria from the inside of two very different pork farms (an intensively confined farm and an open-range farm) to the immediate environment. Samples were taken from the slurry, from the air inside the farms (area 0), and from their immediate surroundings at a distance of 50, 100, and 150 m in four directions (north, south, east, and west). A control sample in the air of a zone far away from human or animal activity was also taken. Identification of isolates was made by means of the matrix-assisted laser desorption-ionization time of flight system. A total of 1,063 isolates were obtained, of which a mere 7 came from the air of the control area. Staphylococci, enterococci, and Enterobacteriaceae were selectively targeted for isolation and represented 48.6, 27.2, and 21.6% of the isolates, respectively. The species identified from the air of surrounding areas ( Enterococcus faecalis, Enterococcus hirae, and Staphylococcus arlettae, mainly) were also present inside the farms studied. The results suggest that air is involved in bacterial dissemination, and pork farms should be considered a potential source of foodborne bacteria that might contaminate surrounding areas, including vegetable orchards. Wind direction appears as a factor involved in bacterial dispersion through the air, but its effect may be conditioned by existing vegetation and orographic conditions.

Evaluation of sampling methods for the detection of pathogenic bacteria on pre-harvest leafy greens

Recent outbreaks of foodborne disease associated with leafy greens have led to increased pre-harvest testing for pathogens and indicator microorganisms. However, the scientific and statistical rationale and the performance attributes for pre-harvest sampling methods are not well understood. The performance of three pre-harvest sampling methods, random, stratified random, and Z-pattern sampling, was evaluated by consideration of their mathematical derivations, computer simulations and field validation. Consideration of the probabilistic basis of the sampling methods indicated that the mean detection rates were similar. However, use of simulation modeling to assess the uncertainty associated with the three sampling methods indicated that the inherent variability of the Z-pattern sampling method was substantially greater than the other two sampling methods. A simulation tool was developed in Matlab that allowed the evaluation of the effectiveness of the three sampling methods. A limited validation study also observed that Z-pattern sampling had higher variability than the other two sampling methods. This study indicates that while the mean detection probabilities for the three sampling methods are similar, the random or stratified random sampling are less variable, particularly when the number of contamination sites or number of samples analyzed are small.

Impact of chlorine dioxide disinfection of irrigation water on the epiphytic bacterial community of baby spinach and underlying soil

The contamination of pathogenic bacteria through irrigation water is a recognized risk factor for fresh produce. Irrigation water disinfection is an intervention strategy that could be applied to reduce the probability of microbiological contamination of crops. Disinfection treatments should be applied ensuring minimum effective doses, which are efficient in inhibiting the microbial contamination while avoiding formation and accumulation of chemical residues. Among disinfection technologies available for growers, chlorine dioxide (ClO₂) represents, after sodium hypochlorite, an alternative disinfection treatment, which is commercially applied by growers in the USA and Spain. However, in most of the cases, the suitability of this treatment has been tested against pathogenic bacteria and low attention have been given to the impact of chemical residues on the bacterial community of the vegetable tissue. The aim of this study was to (i) to evaluate the continual application of chlorine dioxide (ClO₂) as a water disinfection treatment of irrigation water during baby spinach growth in commercial production open fields, and (ii) to determine the subsequent impact of these treatments on the bacterial communities in water, soil, and baby spinach. To gain insight into the changes in the bacterial community elicited by ClO₂, samples of treated and untreated irrigation water as well as the irrigated soil and baby spinach were analyzed using Miseq® Illumina sequencing platform. Next generation sequencing and multivariate statistical analysis revealed that ClO₂ treatment of irrigation water did not affect the diversity of the bacterial community of water, soil and crop, but significant differences were observed in the relative abundance of specific bacterial genera. This demonstrates the different susceptibility of the bacteria genera to the ClO₂ treatment. Based on the obtained results it can be concluded that the phyllosphere bacterial community of baby spinach was more influenced by the soil bacteria community rather than that of irrigation water. In the case of baby spinach, the use of low residual ClO₂ concentrations (approx. 0.25 mg/L) to treat irrigation water decreased the relative abundance of Pseudomonaceae (2.28-fold) and Enterobacteriaceae (2.5-fold) when comparing treated versus untreated baby spinach. Members of these two bacterial families are responsible for food spoilage and foodborne illnesses. Therefore, a reduction of these bacterial families might be beneficial for the crop and for food safety. In general it can be concluded that the constant application of ClO₂ as a disinfection treatment for irrigation water only caused changes in two bacterial families of the baby spinach and soil microbiota, without affecting the major phyla and classes. The significance of these changes in the bacterial community should be further evaluated.

National outbreak of Shiga toxin-producing Escherichia coli O157:H7 linked to mixed salad leaves, United Kingdom, 2016

We investigated a large outbreak of Escherichia coli O157 in the United Kingdom (UK) with 165 cases between 31 May and 29 July 2016. No linked cases were reported in other countries. Cases were predominately female (n = 128) and adult (n = 150), 66 attended hospital and nine had features of haemorrhagic uraemic syndrome. A series of epidemiological studies (case-control, case-case, ingredients-based and venue-based studies) and supply chain investigations implicated mixed salad leaves from Supplier A as the likely outbreak vehicle. Whole genome sequencing (WGS) indicated a link with strains from the Mediterranean and informed the outbreak control team to request that Supplier A cease distributing salad leaves imported from Italy. Microbiological tests of samples of salad leaves from Supplier A were negative. We were unable to confirm the source of contamination or the contaminated constituent leaf although our evidence pointed to red batavia received from Italy as the most likely vehicle. Variations in Shiga toxin-producing E.coli surveillance and diagnosis may have prevented detection of cases outside the UK and highlights a need for greater standardisation. WGS was useful in targeting investigations, but greater coverage across Europe is needed to maximise its potential.

Landscape-Scale Factors Affecting the Prevalence of Escherichia coli in Surface Soil Include Land Cover Type, Edge Interactions, and Soil pH

Escherichia coli is deposited into soil with feces and exhibits subsequent population decline with concomitant environmental selection. Environmentally persistent strains exhibit longer survival times during this selection process, and some strains have adapted to soil and sediments. A georeferenced collection of E. coli isolates was developed comprising 3,329 isolates from 1,428 soil samples that were collected from a landscape spanning the transition from the grasslands to the eastern deciduous forest biomes. The isolate collection and sample database were analyzed together to discover how land cover, site characteristics, and soil chemistry influence the prevalence of cultivable E. coli in surface soil. Soils from forests and pasture lands had equally high prevalences of E. coli Edge interactions were also observed among land cover types, with proximity to forests and pastures affecting the likelihood of E. coli isolation from surrounding soils. E. coli is thought to be more prevalent in sediments with high moisture, but this was observed only in grass- or crop-dominated lands in this study. Because differing E. coli phylogroups are thought to have differing ecology profiles, isolates were also typed using a novel single-nucleotide polymorphism (SNP) genotyping assay. Phylogroup B1 was the dominant group isolated from soil, as has been reported in all other surveys of environmental E. coli Although differences were small, isolates belonging to phylogroups B2 and D were associated with wooded areas, slightly more acidic soils, and soil sampling after rainfall events. In contrast, isolates from phylogroups B1 and E were associated with pasture lands.IMPORTANCE The consensus is that complex niches or life cycles should select for complex genomes in organisms. There is much unexplained biodiversity in E. coli, and its cycling through complex extrahost environments may be a cause. In order to understand the evolutionary processes that lead to adaptation for survival and growth in soil, an isolate collection that associates soil conditions and isolate genome sequences is required. An equally important question is whether traits selected in soil or other extrahost habitats can be transmitted to E. coli residing in hosts via gene flow. The new findings about the distribution of E. coli in soil at the landscape scale (i) enhance our capability to study how extrahost environments influence the evolution of E. coli and other bacteria, (ii) advance our knowledge of the environmental biology of this microbe, and (iii) further affirm the emerging scientific consensus that E. coli in waterways originates from nonpoint sources not associated with human activity or livestock farming.

Microbiological quality of spinach irrigated with reclaimed wastewater and roof-harvest water

AIMS

The effect of reclaimed wastewater (RCW) and roof-harvest rainwater (RHW) on the microbiological quality of irrigated spinach was investigated.

METHODS AND RESULTS

Spinach grown in the controlled environment chamber was irrigated by RCW, RHW or creek water (CW; control water) for 4 weeks, and then six replicate spinach samples from each treatment were collected weekly at 0 h and 24 h postirrigation. Spinach samples were analysed for populations of faecal bacterial indicators and pathogens. Bacterial populations in alternative irrigation water samples were determined by the membrane filtration technique. The RCW samples contained the highest faecal bacterial indicator populations, followed by the CW and RHW throughout the entire study. Irrigation waters containing higher populations of total and faecal coliforms did not necessarily result in higher populations of these bacteria on the irrigated spinach. Higher numbers of E. coli-positive spinach samples were reported from RCW-irrigated spinach, especially with repeated irrigation. Pathogens were not detected from any water or spinach samples.

CONCLUSIONS

Spinach irrigated with RHW did not significantly affect the populations of faecal indicator bacteria when compared with CW-irrigated spinach. Repeat irrigation with RCW is not recommended due to the increased contamination of E. coli on spinach leaves.

SIGNIFICANCE AND IMPACT OF THE STUDY

RHW may potentially be used as alternative irrigation water without deleteriously affecting the microbiological safety of the spinach.

Temporal Stability of Escherichia coli Concentrations in Waters of Two Irrigation Ponds in Maryland

Fecal contamination of water sources is an important water quality issue for agricultural irrigation ponds. Escherichia coli concentrations are commonly used to evaluate recreational and irrigation water quality. We hypothesized that there may exist temporally stable spatial patterns of E. coli concentrations across ponds, meaning that some areas mostly have higher and other areas mostly lower than average concentrations of E. coli To test this hypothesis, we sampled two irrigation ponds in Maryland at nodes of spatial grids biweekly during the summer of 2016. Environmental covariates-temperature, turbidity, conductivity, pH, dissolved oxygen, chlorophyll a, and nutrients-were measured in conjunction with E. coli concentrations. Temporal stability was assessed using mean relative differences between measurements in each location and averaged measurements across ponds. Temporally stable spatial patterns of E. coli concentrations and the majority of environmental covariates were expressed for both ponds. In the pond interior, larger relative mean differences in chlorophyll a corresponded to smaller mean relative differences in E. coli concentrations, with a Spearman's rank correlation coefficient of 0.819. Turbidity and ammonium concentrations were the two other environmental covariates with the largest positive correlations between their location ranks and the E. coli concentration location ranks. Tenfold differences were found between geometric mean E. coli concentrations in locations that were consistently high or consistently low. The existence of temporally stable patterns of E. coli concentrations can affect the results of microbial water quality assessment in ponds and should be accounted for in microbial water quality monitoring design.IMPORTANCE The microbial quality of water in irrigation water sources must be assessed to prevent the spread of microbes that can cause disease in humans because of produce consumption. The microbial quality of irrigation water is evaluated based on concentrations of Escherichia coli as the indicator organism. Given the high spatial and temporal variability of E. coli concentrations in irrigation water sources, recommendations are needed on where and when samples of water have to be taken for microbial analysis. This work demonstrates the presence of a temporally stable spatial pattern in the distributions of E. coli concentrations across irrigation ponds. The ponds studied had zones where E. coli concentrations were mostly higher than average and zones where the concentrations were mostly lower than average over the entire observation period, covering the season when water was used for irrigation. Accounting for the existence of such zones will improve the design and implementation of microbial water quality monitoring.

Microbial quality of irrigation water used in leafy green production in Southern Brazil and its relationship with produce safety

Irrigation water has been recognized as an important microbial risk factor for fruits and vegetables in many production areas, but there is still a lack of information about how the microbiological quality of different irrigation water sources and climatic conditions influence the safety of vegetables produced in Brazil. This study evaluated the distribution of generic E. coli and the prevalence of E. coli O157:H7 in two different water sources (ponds and streams bordering farmlands and urban areas) used for irrigation and on commercially produced lettuces in Southern Brazil. We also evaluated the effect of agricultural factors and meteorological conditions in the potential contamination of water and produce samples. A longitudinal study was conducted on four farms during a year (July 2014 to August 2015). The results showed generic E. coli prevalence of 84.8% and 38.3% in irrigation water samples and on lettuces, respectively, indicating irrigation water as an important source of contamination of lettuces. No significant differences were detected in the counts of E. coli between the two different surface water sources. The climatic conditions, particularly rainfall and environmental temperature, have influenced the high concentration of E. coli. The highest loads of E. coli in irrigation water and on lettuces were found during the warmest time of the year. E. coli O157:H7 was detected by qualitative polymerase chain reaction (qPCR) in 13 water samples but only 4 were confirmed by isolation in culture media.

Quantitative contamination assessment of Escherichia coli in baby spinach primary production in Spain: Effects of weather conditions and agricultural practices

A quantitative microbial contamination model of Escherichia coli during primary production of baby spinach was developed. The model included only systematic contamination routes (e.g. soil and irrigation water) and it was used to evaluate the potential impact of weather conditions, agricultural practices as well as bacterial fitness in soil on the E. coli levels present in the crop at harvest. The model can be used to estimate E. coli contamination of baby spinach via irrigation water, via soil splashing due to irrigation water or rain events, and also including the inactivation of E. coli on plants due to solar radiation during a variable time of culturing before harvest. Seasonality, solar radiation and rainfall were predicted to have an important impact on the E. coli contamination. Winter conditions increased E. coli prevalence and levels when compared to spring conditions. As regards agricultural practices, both water quality and irrigation system slightly influenced E. coli levels on baby spinach. The good microbiological quality of the irrigation water (average E. coli counts in positive water samples below 1 log/100mL) could have influenced the differences observed among the tested agricultural practices (water treatment and irrigation system). This quantitative microbial contamination model represents a preliminary framework that assesses the potential impact of different factors and intervention strategies affecting E. coli concentrations at field level. Taking into account that E. coli strains may serve as a surrogate organism for enteric bacterial pathogens, obtained results on E. coli levels on baby spinach may be indicative of the potential behaviour of these pathogens under defined conditions.

Modeling the interannual variability of microbial quality metrics of irrigation water in a Pennsylvania stream

Knowledge of the microbial quality of irrigation waters is extremely limited. For this reason, the US FDA has promulgated the Produce Rule, mandating the testing of irrigation water sources for many farms. The rule requires the collection and analysis of at least 20 water samples over two to four years to adequately evaluate the quality of water intended for produce irrigation. The objective of this work was to evaluate the effect of interannual weather variability on surface water microbial quality. We used the Soil and Water Assessment Tool model to simulate E. coli concentrations in the Little Cove Creek; this is a perennial creek located in an agricultural watershed in south-eastern Pennsylvania. The model performance was evaluated using the US FDA regulatory microbial water quality metrics of geometric mean (GM) and the statistical threshold value (STV). Using the 90-year time series of weather observations, we simulated and randomly sampled the time series of E. coli concentrations. We found that weather conditions of a specific year may strongly affect the evaluation of microbial quality and that the long-term assessment of microbial water quality may be quite different from the evaluation based on short-term observations. The variations in microbial concentrations and water quality metrics were affected by location, wetness of the hydrological years, and seasonality, with 15.7-70.1% of samples exceeding the regulatory threshold. The results of this work demonstrate the value of using modeling to design and evaluate monitoring protocols to assess the microbial quality of water used for produce irrigation.

Impacts of Climate and Management Variables on the Contamination of Preharvest Leafy Greens with Escherichia coli

The observed seasonality of foodborne disease suggests that climatic conditions play a role and that changes in the climate may affect the presence of pathogens. However, it is hard to determine whether this effect is direct or whether it works indirectly through other factors, such as farm management. This study aimed to identify the climate and management variables that are associated with the contamination (presence and concentration) of leafy green vegetables with E. coli. This study used data about E. coli contamination from 562 leafy green vegetables (lettuce and spinach) samples taken between 2011 and 2013 from 23 open-field farms in Belgium, Brazil, Egypt, Norway, and Spain. Mixed-effect logistic and linear regression models were used to study the statistical relationship between the dependent and independent variables. Climate variables and agricultural management practices together had a systematic influence on E. coli presence and concentration. The variables important for E. coli presence included the minimum temperature of the sampling day (odds ratio = 1.47), region, and application of inorganic fertilizer. The variables important for concentration (R(2) = 0.75) were the maximum temperature during the 3 days before sampling and the region. Temperature had a stronger influence (had a significant parameter estimate and the highest R(2)) than did management practices on E. coli presence and concentration. Region was a variable that masked many management variables, including rainwater, surface water, manure, inorganic fertilizer, and spray irrigation. Climate variables had a positive relationship with E. coli presence and concentration. Temperature, irrigation water type, fertilizer type, and irrigation method should be systematically considered in future studies of fresh produce safety.

Validation of a Previously Developed Geospatial Model That Predicts the Prevalence of Listeria monocytogenes in New York State Produce Fields

Technological advancements, particularly in the field of geographic information systems (GIS), have made it possible to predict the likelihood of foodborne pathogen contamination in produce production environments using geospatial models. Yet, few studies have examined the validity and robustness of such models. This study was performed to test and refine the rules associated with a previously developed geospatial model that predicts the prevalence of Listeria monocytogenes in produce farms in New York State (NYS). Produce fields for each of four enrolled produce farms were categorized into areas of high or low predicted L. monocytogenes prevalence using rules based on a field's available water storage (AWS) and its proximity to water, impervious cover, and pastures. Drag swabs (n = 1,056) were collected from plots assigned to each risk category. Logistic regression, which tested the ability of each rule to accurately predict the prevalence of L. monocytogenes, validated the rules based on water and pasture. Samples collected near water (odds ratio [OR], 3.0) and pasture (OR, 2.9) showed a significantly increased likelihood of L. monocytogenes isolation compared to that for samples collected far from water and pasture. Generalized linear mixed models identified additional land cover factors associated with an increased likelihood of L. monocytogenes isolation, such as proximity to wetlands. These findings validated a subset of previously developed rules that predict L. monocytogenes prevalence in produce production environments. This suggests that GIS and geospatial models can be used to accurately predict L. monocytogenes prevalence on farms and can be used prospectively to minimize the risk of preharvest contamination of produce.

Spatial and Temporal Factors Associated with an Increased Prevalence of Listeria monocytogenes in Spinach Fields in New York State

While rain and irrigation events have been associated with an increased prevalence of foodborne pathogens in produce production environments, quantitative data are needed to determine the effects of various spatial and temporal factors on the risk of produce contamination following these events. This study was performed to quantify these effects and to determine the impact of rain and irrigation events on the detection frequency and diversity of Listeria species (including L. monocytogenes) and L. monocytogenes in produce fields. Two spinach fields, with high and low predicted risks of L. monocytogenes isolation, were sampled 24, 48, 72, and 144 to 192 h following irrigation and rain events. Predicted risk was a function of the field's proximity to water and roads. Factors were evaluated for their association with Listeria species and L. monocytogenes isolation by using generalized linear mixed models (GLMMs). In total, 1,492 (1,092 soil, 334 leaf, 14 fecal, and 52 water) samples were collected. According to the GLMM, the likelihood of Listeria species and L. monocytogenes isolation from soil samples was highest during the 24 h immediately following an event (odds ratios [ORs] of 7.7 and 25, respectively). Additionally, Listeria species and L. monocytogenes isolates associated with irrigation events showed significantly lower sigB allele type diversity than did isolates associated with precipitation events (P = <0.001), suggesting that irrigation water may be a point source of L. monocytogenes contamination. Small changes in management practices (e.g., not irrigating fields before harvest) may therefore reduce the risk of L. monocytogenes contamination of fresh produce.

Risk Factors for Salmonella, Shiga Toxin-Producing Escherichia coli and Campylobacter Occurrence in Primary Production of Leafy Greens and Strawberries

The microbiological sanitary quality and safety of leafy greens and strawberries were assessed in the primary production in Belgium, Brazil, Egypt, Norway and Spain by enumeration of Escherichia coli and detection of Salmonella, Shiga toxin-producing E. coli (STEC) and Campylobacter. Water samples were more prone to containing pathogens (54 positives out of 950 analyses) than soil (16/1186) and produce on the field (18/977 for leafy greens and 5/402 for strawberries). The prevalence of pathogens also varied markedly according to the sampling region. Flooding of fields increased the risk considerably, with odds ratio (OR) 10.9 for Salmonella and 7.0 for STEC. A significant association between elevated numbers of generic E. coli and detection of pathogens (OR of 2.3 for STEC and 2.7 for Salmonella) was established. Generic E. coli was found to be a suitable index organism for Salmonella and STEC, but to a lesser extent for Campylobacter. Guidelines on frequency of sampling and threshold values for E. coli in irrigation water may differ from region to region.