Summer meeting 2007 the problems with fresh produce: an overview

Biological Control of Escherichia coli O157:H7 in Dairy Manure-Based Compost Using Competitive Exclusion Microorganisms

BACKGROUND

Animal manure-based compost is a valuable organic fertilizer and biological soil amendment. To ensure the microbiological safety of compost products, the effectiveness of competitive exclusion microorganisms (CE) in reducing Escherichia coli O157:H7 in dairy manure-based compost was evaluated.

METHODS

A cocktail of E. coli O157:H7 strains were inoculated into dairy compost along with CE strains isolated from compost, and the reduction in E. coli O157:H7 by CE was determined in compost with 20%, 30%, and 40% moisture levels at 22 °C and 30 °C under laboratory conditions, as well as in fall, winter, and summer seasons under greenhouse settings.

RESULTS

Under lab conditions, CE addition resulted in 1.1-3.36 log reductions in E. coli O157:H7 in compost, with enhanced pathogen reduction by higher moisture and lower temperature. In the greenhouse, >99% of the E. coli O157:H7 population in compost with ≥30% moisture due to cross-contamination can be effectively inactivated by CE within 2 days during colder seasons. However, it took ≥8 days to achieve the same level of reduction for heat-adapted E. coli O157:H7 cells.

CONCLUSIONS

Our results demonstrated that the competitive exclusion of microorganisms can be an effective tool for controlling foodborne pathogens in compost and reducing the potential for soil and crop contamination.

Multi-laboratory validation study of a real-time PCR method for detection of Salmonella in baby spinach

The FDA Bacteriological Analytical Manual (BAM) Salmonella culture method takes at least 3 days for a presumptive positive result. The FDA developed a quantitative PCR (qPCR) method to detect Salmonella from 24-h preenriched cultures, using ABI 7500 PCR system. The qPCR method has been evaluated as a rapid screening method for a broad range of foods by single laboratory validation (SLV) studies. The present multi-laboratory validation (MLV) study was aimed to measure the reproducibility of this qPCR method and compare its performance with the culture method. Sixteen laboratories participated in two rounds of MLV study to analyze twenty-four blind-coded baby spinach test portions each. The first round yielded ∼84% and ∼82% positive rates across laboratories for the qPCR and culture methods, respectively, which were both outside the fractional range (25%-75%) required for fractionally inoculated test portions by the FDA's Microbiological Method Validation Guidelines. The second round yielded ∼68% and ∼67% positive rates. The relative level of detection (RLOD) for the second-round study was 0.969, suggesting that qPCR and culture methods had similar sensitivity (p > 0.05). The study demonstrated that the qPCR yields reproducible results and is sufficiently sensitive and specific for the detection of Salmonella in food.

Lytic Escherichia phage OSYSP acts additively and synergistically with gaseous ozone against Escherichia coli O157:H7 on spinach leaves

Bacteriophage and gaseous ozone are evolving as meritorious alternatives to conventional sanitizers in food postharvest applications. Here, we investigated the efficacy of sequential treatments of a lytic bacteriophage and gaseous ozone, during vacuum cooling of fresh produce, against Escherichia coli O157:H7. Spinach leaves were spot-inoculated with 10⁵-10⁷ CFU g^-1 E. coli O157:H7 B6-914 and treated with Escherichia phage OSYSP spray (10⁹ PFU g^-1), gaseous ozone, or their combination. Vacuum cooling, which preceded or followed phage application but ran concomitantly with ozone treatment, was performed in a custom-made vessel at the following process sequence: vacuum to 28.5 in. Hg, vessel pressurization to 10 psig with gas containing 1.5 g ozone/kg gas-mix, holding for 30 min, and vessel depressurization to ambient pressure. Bacteriophage or gaseous ozone inactivated E. coli O157:H7, applied at different initial populations on spinach leaves, by 1.7-2.0 or 1.8-3.5 log CFU g^-1, respectively. At the high inoculum levels tested (7.1 log CFU g^-1), sequential treatments of phage and ozone reduced E. coli O157:H7 population by 4.0 log CFU g^-1, but when treatment order was reversed (i.e., ozone followed by bacteriophage), the combination synergistically decreased pathogen's population on spinach leaves by 5.2 log CFU g^-1. Regardless the antibacterial application order, E. coli O157:H7 populations, applied initially at ~ 10⁵ CFU g^-1, were reduced below the enumeration method's detection level (i.e., < 10¹ CFU g^-1). The study proved that bacteriophage-ozone combination, applied in conjunction with vacuum cooling, is a potent pathogen intervention strategy in fresh produce post-harvest applications.

Microorganisms in Organic Food-Issues to Be Addressed

The review aimed to analyse the latest data on microorganisms present in organic food, both beneficial and unwanted. In conclusion, organic food's microbial quality is generally similar to that of conventionally produced food. However, some studies suggest that organic food may contain fewer pathogens, such as antibiotic-resistant strains, due to the absence of antibiotic use in organic farming practices. However, there is little discussion and data regarding the importance of some methods used in organic farming and the risk of food pathogens presence. Concerning data gaps, it is necessary to plan and perform detailed studies of the microbiological safety of organic food, including foodborne viruses and parasites and factors related to this method of cultivation and specific processing requirements. Such knowledge is essential for more effective management of the safety of this food. The use of beneficial bacteria in organic food production has not yet been widely addressed in the scientific literature. This is particularly desirable due to the properties of the separately researched probiotics and the organic food matrix. The microbiological quality of organic food and its potential impact on human health is worth further research to confirm its safety and to assess the beneficial properties resulting from the addition of probiotics.

Possible sources of Listeria monocytogenes contamination of fresh-cut apples and antimicrobial interventions during antibrowning treatments: a review

Fresh-cut apples, being rich in antioxidants and other nutrients, have emerged as popular snacks in restaurants, at home and in school lunch programs, partially due to freshness, convenience, and portion size availability. Two major challenges in processing fresh-cut apples are browning of cut surfaces and contamination with human pathogens. Regarding human pathogens, contamination by Listeria monocytogenes is a major concern, as evidenced by two recent outbreaks of whole apples and numerous recalls of fresh-cut apples. Antibrowning agents currently used by the industry have little to no antimicrobial properties. The present review discusses possible origins of L. monocytogenes in fresh-cut apples, including contaminated whole apples, and contamination via the processing environment and the equipment in fresh-cut facilities. Treatment with antibrowning solutions could be an opportunity for Listeria contamination and represents the last chance to inactivate pathogens. The discussion is focused on the antibrowning treatments where formulations and coatings with antibrowning and antimicrobial properties have been developed and evaluated against Listeria and other microorganisms. In addition, several research needs and considerations are discussed to further reduce the chance of pathogen contamination on fresh-cut apples.

Eugenol nanoemulsion inactivates Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 on cantaloupes without affecting rind color

Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7 are the major foodborne pathogens that have been implicated in outbreaks related to consumption of contaminated cantaloupes. Current chlorine-based decontamination strategies are not completely effective for inactivating the aforementioned pathogens on cantaloupes, especially in the presence of organic matter. This study investigated the efficacy of eugenol nanoemulsion (EGNE) wash treatments in inactivating L. monocytogenes, Salmonella spp., and E. coli O157:H7 on the surface of cantaloupes. In addition, the efficacy of EGNE in inhibiting the growth of the three pathogens on cantaloupes during refrigerated and room temperature storage of 5 days was investigated. Moreover, the effect of EGNE wash treatment on cantaloupe color was assessed using a Miniscan® XE Plus. The EGNE was prepared with either Tween 80 (TW) or a combination of Gum arabic and Lecithin (GA) as emulsifiers. The cantaloupe rind was washed with EGNE (0.3, 0.6, and 1.25%), in presence or absence of 5% organic load, for 1, 5, or 10 min at 25°C. Enumeration of surviving pathogens on cantaloupe was performed by serial dilution and plating on Oxford, XLD or SMA agar followed by incubation at 37°C for 24–48 h. EGNE-GA and EGNE-TW wash significantly reduced all three pathogens by at least 3.5 log CFU/cm2 as early as 5 min after treatment. EGNE-GA at 1.25% inactivated L. monocytogenes, E. coli O157:H7 and S. Enteritidis on cantaloupes to below the detectable limit within 5 and 10 min of treatment, respectively (~4 log CFU/cm2, P &lt; 0.05). EGNE treatments significantly reduced the survival of L. monocytogenes, S. Enteritidis, and E. coli O157:H7 on cantaloupe by at least 6 log CFU/cm2 at day 5 of storage at 25 and 4°C (P &lt; 0.05). Presence of organic matter did not modulate the antimicrobial efficacy of nanoemulsion treatments (P &gt; 0.05). EGNE treatments did not affect the rind color of cantaloupes (P &gt; 0.05). In conclusion, eugenol nanoemulsions could potentially be used as a natural sanitizer to inactivate foodborne pathogens on cantaloupes. Further investigations in an industry setting are warranted.

A Review of Essential Oils as Antimicrobials in Foods with Special Emphasis on Fresh Produce

ABSTRACT

Consumer safety concerns over established fresh produce washing methods and the demand for organic and clean-label food has led to the exploration of novel methods of produce sanitization. Essential oils (EOs), which are extracted from plants, have potential as clean-label sanitizers because they are naturally derived and act as antimicrobials and antioxidants. In this review, the antimicrobial effects of EOs are explored individually and in combination, as emulsions, combined with existing chemical and physical preservation methods, incorporated into films and coatings, and in vapor phase. We examined combinations of EOs with one another, with EO components, with surfactants, and with other preservatives or preservation methods to increase sanitizing efficacy. Components of major EOs were identified, and the chemical mechanisms, potential for antibacterial resistance, and effects on organoleptic properties were examined. Studies have revealed that EOs can be equivalent or better sanitizing agents than chlorine; nevertheless, concentrations must be kept low to avoid adverse sensory effects. For this reason, future studies should address the maximum permissible EO concentrations that do not negatively affect organoleptic properties. This review should be beneficial to food scientists or industry personnel interested in the use of EOs for sanitization and preservation of foods, including fresh produce.

HIGHLIGHTS

Regulation Mechanisms of Virulence Genes in Enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is one of the most common E. coli pathotypes reported to cause several outbreaks of foodborne illnesses. EHEC is a zoonotic pathogen, and ruminants, especially cattle, are considered important reservoirs for the most common EHEC serotype, E. coli O157:H7. Humans are infected indirectly through the consumption of food (milk, meat, leafy vegetables, and fruits) and water contaminated by animal feces or direct contact with carrier animals or humans. E. coli O157:H7 is one of the most frequently reported causes of foodborne illnesses in developed countries. It employs two essential virulence mechanisms to trigger damage to the host. These are the development of attaching and effacing (AE) phenotypes on the intestinal mucosa of the host and the production of Shiga toxin (Stx) that causes hemorrhagic colitis and hemolytic uremic syndrome. The AE phenotype is controlled by the pathogenicity island, the locus of enterocyte effacement (LEE). The induction of both AE and Stx is under strict and highly complex regulatory mechanisms. Thus, a good understanding of these mechanisms, major proteins expressed, and environmental cues involved in the regulation of the expression of the virulence genes is vital to finding a method to control the colonization of reservoir hosts, especially cattle, and disease development in humans. This review is a concise account of the current state of knowledge of virulence gene regulation in the LEE-positive EHEC.

The live bacterial load and microbiota composition of prepacked "ready-to-eat" leafy greens during household conditions, with special reference to E. coli

Ready-to-eat (RTE) leafy greens are popular products that unfortunately have been associated with numerous foodborne illness outbreaks. Since the influence of consumer practices is essential for their quality and safety, the objective of this study was to analyze the microbiota of RTE products throughout shelf life during simulated household conditions. Products from different companies were analyzed in terms of plate counts, and resealed and unopened packages were compared. High bacterial loads were found, up to a total plate count of 9.6 log₁₀ CFU/g, and Enterobacteriaceae plate counts up to 6.0 CFU/g on the expiration date. The effect of consumer practice varied, thus no conclusions regarding resealed or unopened bags could be drawn. The tested products contained opportunistic pathogens, such as Enterobacter homaechei, Hafnia paralvei and Pantoea agglomerans. Amplicon sequencing revealed that the relative abundance of major taxonomic groups changed during shelf life; Pseudomonadaceae and Xanthomonadaceae decreased, while Flavobacteriaceae and Marinomonadaceae inceased. Inoculation with E. coli CCUG 29300^T showed that the relative abundance of Escherichia-Shigella was lower on rocket than on other tested leafy greens. Inoculation with E. coli strain 921 indicate growth at the beginning of shelf-life time, while E. coli 731 increases at the end, seemingly able to adapt to cold storage conditions. The high levels of live microorganisms, the detection of opportunistic pathogens, and the ability of E. coli strains to grow at refrigeration temperature raise concerns and indicate that the shelf life may be shortened to achieve a safer product. Due to variations between products, further studies are needed to define how long the shelf-life of these products should be, to ensure a safe product even at the end of the shelf-life period.

Food Safety Governance and Guardianship: The Role of the Private Sector in Addressing the EU Ethylene Oxide Incident

Sesame seeds within the European Union (EU) are classified as foods not of animal origin. Two food safety issues associated with sesame seeds have emerged in recent years, i.e., Salmonella contamination and the presence of ethylene oxide. Fumigation with ethylene oxide to reduce Salmonella in seeds and spices is not approved in the EU, so its presence in sesame seeds from India was a sentinel incident sparking multiple trans-European product recalls between 2020-2021. Following an interpretivist approach, this study utilises academic and grey sources including data from the EU Rapid Alert System for Food and Feed (RASFF) database to inform a critical appraisal of current EU foods not of animal origin legislation and associated governance structures and surveillance programs. This is of particular importance as consumers are encouraged towards plant-based diets. This study shows the importance of collaborative governance utilizing data from company testing and audits as well as official regulatory controls to define the depth and breadth of a given incident in Europe. The development of reflexive governance supported by the newest technology (e.g., blockchain) might be of value in public-private models of food safety governance. This study contributes to the literature on the adoption of risk-based food safety regulation and the associated hybrid public-private models of food safety governance where both regulators and private organizations play a vital role in assuring public health.

Surface enhanced Raman scattering for the multiplexed detection of pathogenic microorganisms: towards point-of-use applications

Surface enhanced Raman scattering (SERS) is a technique that demonstrates a number of advantages for the rapid, specific and sensitive detection of pathogenic microorganisms. In this review, an overview of label-free and label-based SERS approaches, including microfluidics, nucleic acid detection and immunoassays, for the multiplexed detection of pathogenic bacteria and viruses from the last decade will be discussed, as well as their transition into promising point-of-use detection technologies in industrial and medical settings.

Microbial Quality Assessment and Efficacy of Low-Cost Disinfectants on Fresh Fruits and Vegetables Collected from Urban Areas of Dhaka, Bangladesh

This study aimed to examine the total viable bacteria (TVBC); total coliform (TCC); fecal coliform (TFC); pathogenic Pseudomonas spp., Staphylococcus aureus, and total fungi (TF); and the effect of different low-cost disinfectants (sterile water, salt water, blanched, and vinegar) in decontamination of 12 types of fruit and 10 types of vegetables. In fruit samples, the lowest TVBC was enumerated at 3.18 ± 0.27 log CFU/g in Indian gooseberry and the highest at 6.47 ± 0.68 log CFU/g in guava. Staphylococci (2.04 ± 0.53-5.10 ± 0.02 log CFU/g), Pseudomonas (1.88 ± 0.03-5.38 ± 0.08 log CFU/g), and total fungi (2.60 ± 0.18-7.50 ± 0.15 log CFU/g) were found in all fruit samples; however, no Salmonella was detected in fruit samples. Similarly, the lowest TVBC recorded 5.67± 0.49 log CFU/g in cucumber and the highest 7.37 ± 0.06 log CFU/g in yard long bean. The Staphylococci (3.48 ± 0.13-4.81 ± 0.16 log CFU/g), Pseudomonas (3.57± 0.21- 4.75 ± 0.23 log CFU/g), TCC (1.85 ± 1.11-56.50 ± 37.14 MPN/g), TFC (1.76 ± 0.87- 3.78 ± 3.76 MPN/g), and TF (3.79 ± 0.18-4.40 ± 0.38 log CFU/g) were recorded in all vegetables samples, but no Salmonella was detected in yard long bean, pointed gourd, carrot, tomato, cucumber, or brinjal. However, vinegar showed the highest microbial load reduction of selected fruit and vegetables among the different treatments. With vinegar treatment, the highest reduction of TVBC (1.61-log) and TF (2.54-log) was observed for fruits, and TVBC (2.31-log) and TF (2.41-log) for vegetables. All the disinfectant treatments resulted in significant (p < 0.01) bacterial load reduction compared to control for the studied fruits and vegetable samples.

Synergistic effect of citric acid and xenon light for inactivating foodborne pathogens on spinach leaves

The aim of this study was to evaluate the synergistic antimicrobial effect of xenon light (XL) and citric acid (CA) combination against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach leaves and determine the effect of XL-CA combination on quality of spinach leaves. The XL-CA combined treatment for 8 min synergistically decreased the cell counts of E. coli O157:H7 and S. Typhimurium by 5.25 and 5.05 log CFU/cm², respectively, and additively decreased the L. monocytogenes cells by 5.02 log unit on spinach. The mechanisms underlying synergistic lethal effect of the XL-CA combination were investigated. Qualitative and quantitative analyses revealed that the bacterial cell membrane damage was strongly associated with the synergistic antimicrobial effect of the XL-CA combination. Additionally, treatment with XL-CA combination for 8 min did not affect the quality attributes (color, total phenol contents, and texture) of spinach leaves. These results suggest that the XL-CA combination treatment can be effectively used to control major pathogens on fresh produce.

Quantification of Survival and Transfer of Salmonella on Fresh Cucumbers during Waxing

ABSTRACT

Cucumbers found in retail markets are often waxed to improve visual appeal and retard moisture loss. This waxing may affect bacterial survival, and the waxing process may facilitate cross-contamination between cucumbers. This study assessed the survival of Salmonella on waxed and unwaxed cucumbers and the potential for Salmonella cross-contamination during the waxing process. Fresh waxed or unwaxed cucumbers were spot inoculated with a cocktail of Salmonella enterica strains. Three different wax coatings (mineral oil, vegetable oil, or petroleum wax) were manually applied to unwaxed cucumbers using polyethylene brushes. Salmonella transfer from inoculated cucumbers to the brush or to uninoculated cucumbers was quantified. Higher Salmonella concentrations were observed on waxed cucumbers during the first 3 days of storage, but the final concentration on unwaxed cucumbers was higher than on waxed cucumbers at the end of storage, regardless of storage temperature. The wax formulation did affect the survival of Salmonella inoculated directly into waxes, with a significant decline in Salmonella populations observed in vegetable-based wax coating but with populations unchanged over 7 days at 7 or 21°C in mineral oil-based and petroleum-based waxes. Salmonella cells could transfer from inoculated unwaxed cucumbers to brushes used for waxing and then to uninoculated cucumbers during waxing. A significantly higher log percentage of transfer to brushes was observed when cucumbers were waxed with vegetable oil (0.71 log percent, P = 0.00441) than with mineral oil (0.06 log percent) or petroleum (0.05 log percent). Transfer to uninoculated cucumbers via brushes was also quantified (0.18 to 0.35 log percent transfer). Salmonella remaining on contaminated cucumbers after waxing could be detected for up to 7 days, and Salmonella survived better on cucumbers treated with a petroleum-based wax. These findings should be useful in managing the risk of Salmonella contamination in cucumbers during postharvest handling.

HIGHLIGHTS

Adhesion and removal of E. coli K12 as affected by leafy green produce epicuticular wax composition, surface roughness, produce and bacterial surface hydrophobicity, and sanitizers

Contaminated leafy vegetables have been associated with high-profile outbreaks causing severe illnesses. A good understanding of the interactions between human pathogen and produce is important for developing improved food safety control strategies. Currently, the role played by produce surface physiochemical characteristics in such interactions is not well-understood. This work was performed to examine the effects of produce physiochemical characteristics, including surface roughness, epicuticular wax composition, and produce and bacteria surface hydrophobicity on attachment and removal of vegetative bacteria. Escherichia coli K12 was used as a model microorganism to evaluate attachment to and removal from five leafy green vegetables after washing with selected sanitizers. A detailed epicuticular wax component analysis was conducted and the changes of wax composition after sanitation were also evaluated. The results showed that E. coli K12 removal is positively correlated with alkanes, ketones, and total wax content on leaf surfaces. Vegetables with high surface wax content had less rough leaf surfaces and more bacterial removal than the low wax produce. Produce surface roughness positively correlated to E. coli K12 adhesion and negatively correlated to removal. The cells preferentially attached to cut vegetable surfaces, with up to 1.49 times more attachment than on leaf adaxial surfaces.

On farm interventions to minimise Campylobacter spp. contamination in chicken

1. This review explores current and proposed on-farm interventions and assess the potential of these interventions against Campylobacter spp. 2. Interventions such as vaccination, feed/water-additives and, most importantly, consistent biosecurity, exhibit potential for the effective control of this pathogen and its dissemination within the food chain. 3. Due to the extensive diversity in the Campylobacter spp. genome and surface-expressed proteins, vaccination of poultry is not yet regarded as a completely effective strategy. 4. The acidification of drinking water through the addition of organic acids has been reported to decrease the risk of Campylobacter spp. colonisation in broiler flocks. Whilst this treatment alone will not completely protect birds, use of water acidification in combination with in-feed measures to further reduce the level of Campylobacter spp. colonisation in poultry may be an option meriting further exploration. 5. The use of varied types of feed supplements to reduce the intestinal population and shedding rate of Campylobacter spp. in poultry is an area of growing interest in the poultry industry. Such supplements include pro - and pre-biotics, organic acids, bacteriocins and bacteriophage, which may be added to feed and water. 6. From the literature, it is clear that a distinct, albeit not unexpected, difference between the performance of in-feed interventions exists when examined in vitro compared to those determined in in vivo studies. It is much more likely that pooling some of the discussed approaches in the in-feed tool kit will provide an answer. 7. Whilst on-farm biosecurity is essential to maintain a healthy flock and reduce disease transmission, even the most stringent biosecurity measures may not have sufficient, consistent and predictable effects in controlling Campylobacter spp. Furthermore, the combination of varied dietary approaches and improved biosecurity measures may synergistically improve control.

The Composition of Microbial Communities in Six Streams, and Its Association With Environmental Conditions, and Foodborne Pathogen Isolation

Surface water used for produce production is a potential source of pre-harvest contamination with foodborne pathogens. Decisions on how to mitigate food safety risks associated with pre-harvest water use currently rely on generic Escherichia coli-based water quality tests, although multiple studies have suggested that E. coli levels are not a suitable indicator of the food safety risks under all relevant environmental conditions. Hence, improved understanding of spatiotemporal variability in surface water microbiota composition is needed to facilitate identification of alternative or supplementary indicators that co-occur with pathogens. To this end, we aimed to characterize the composition of bacterial and fungal communities in the sediment and water fractions of 68 agricultural water samples collected from six New York streams. We investigated potential associations between the composition of microbial communities, environmental factors and Salmonella and/or Listeria monocytogenes isolation. We found significantly different composition of fungal and bacterial communities among sampled streams and among water fractions of collected samples. This indicates that geography and the amount of sediment in a collected water sample may affect its microbial composition, which was further supported by identified associations between the flow rate, turbidity, pH and conductivity, and microbial community composition. Lastly, we identified specific microbial families that were weakly associated with the presence of Salmonella or Listeria monocytogenes, however, further studies on samples from additional streams are needed to assess whether identified families may be used as indicators of pathogen presence.

AB_SA: Accessory genes-Based Source Attribution - tracing the source of Salmonella enterica Typhimurium environmental strains

The partitioning of pathogenic strains isolated in environmental or human cases to their sources is challenging. The pathogens usually colonize multiple animal hosts, including livestock, which contaminate the food-production chain and the environment (e.g. soil and water), posing an additional public-health burden and major challenges in the identification of the source. Genomic data opens up new opportunities for the development of statistical models aiming to indicate the likely source of pathogen contamination. Here, we propose a computationally fast and efficient multinomial logistic regression source-attribution classifier to predict the animal source of bacterial isolates based on 'source-enriched' loci extracted from the accessory-genome profiles of a pangenomic dataset. Depending on the accuracy of the model's self-attribution step, the modeller selects the number of candidate accessory genes that best fit the model for calculating the likelihood of (source) category membership. The Accessory genes-Based Source Attribution (AB_SA) method was applied to a dataset of strains of Salmonella enterica Typhimurium and its monophasic variant (S. enterica 1,4,[5],12:i:-). The model was trained on 69 strains with known animal-source categories (i.e. poultry, ruminant and pig). The AB_SA method helped to identify 8 genes as predictors among the 2802 accessory genes. The self-attribution accuracy was 80 %. The AB_SA model was then able to classify 25 of the 29 S. enterica Typhimurium and S. enterica 1,4,[5],12:i:- isolates collected from the environment (considered to be of unknown source) into a specific category (i.e. animal source), with more than 85 % of probability. The AB_SA method herein described provides a user-friendly and valuable tool for performing source-attribution studies in only a few steps. AB_SA is written in R and freely available at https://github.com/lguillier/AB_SA.

Parasitic contamination and public health risk of commonly consumed vegetables in Ibadan-Nigeria

Introduction

vegetables form a major component of the human diet. However, poor agronomic practices may put consumers at risk of parasitic infections. This study evaluated the parasitic contamination of vegetables grown in selected farms in Ibadan, Nigeria.

Methods

Two hundred and eighty vegetable species: African eggplant (Solanum macrocarpon), lettuce (Lactuca sativa), cucumber (Brassica oleracea), spinach (Amaranthus cruentus), white jute (Corchorus olitorius), pumpkin (Telfaria occidentalis), green pepper (Capsicum sp.), okro (Abelmoschus esculentus), quill grass (Celosia argenta L), tomato (Lycopersicum sativus) were collected from farms within Ibadan. Samples were washed in water, and the resulting washing solution was filtered and centrifuged to concentrate the parasitic stages. Sediments were examined by iodine and modified Ziehl-Neelsen stained smears technique.

Results

parasites were detected in 14 (5.0%, 95% CI 32.6%-67.3%) of samples. The highest contaminated vegetable was white jute 32.1 (95% CI 17.9%-50.6%), followed by pumpkin 7.1(95% CI 1.9-22.6), quill grass 7.1% (95% CI 1.9-22.6) and lettuce 3.5 (95% CI 0.6-17.7). The commonest parasites were Strongyloides stercoralis larvae 42.9 (95% CI 21.3-67.4), Entamoeba histolytica/E.dipaar 21.4 (95% CI 7.5-47.5), Trichostrongylus spp 21.4 (95% CI 21.3-67.4), and Ascaris sp. 14.3 (95% CI 4.0-39.9).

Conclusion

these findings provide evidence of contamination of vegetables from farms in Ibadan with parasites of public health importance. Information on best practices should be designed, packaged and disseminated through appropriate channels to enhance positive behavior change among farmers.

Cold plasma enhances the efficacy of aerosolized hydrogen peroxide in reducing populations of Salmonella Typhimurium and Listeria innocua on grape tomatoes, apples, cantaloupe and romaine lettuce

In the present study, we investigated whether cold plasma activation affected the efficacy of aerosolized hydrogen peroxide against S. Typhimurium and L. innocua. Stem scars and smooth surfaces of grape tomatoes, surfaces of Granny Smith apples and Romaine lettuce (both midrib and upper leaves) and cantaloupe rinds were inoculated with two-strain cocktails of S. Typhimurium and 3-strain cocktails of L. innocua. The inoculated samples were treated with 7.8% aerosolized H2O2 with and without cold plasma for various times. For all fresh produce items and surfaces, cold plasma significantly (P < 0.05) improved the efficacy of aerosolized H2O2 against Salmonella and L. innocua. Without cold plasma activation, H2O2 aerosols only reduced populations of Salmonella by 1.54-3.17 log CFU/piece while H2O2 with cold plasma achieved 2.35-5.50 log CFU/piece reductions of Salmonella. L. innocua was more sensitive to the cold plasma-activated H2O2 than Salmonella. Cold plasma activated H2O2 aerosols reduced Listeria populations by more than 5 log CFU/piece on all types and surfaces of fresh produce except for the tomato stem scar area. Without cold plasma, the reductions by H2O2 were only 1.35-3.77 log CFU/piece. Overall, our results demonstrated that cold plasma activation significantly enhanced the efficacy of H2O2 mist against bacteria on fresh produce.

Environmental and Adaptive Changes Necessitate a Paradigm Shift for Indicators of Fecal Contamination

Changes in the occurrence, distribution, and seasonal variation of waterborne pathogens due to global climate change may increase the risk of human exposure to these microorganisms, thus heightening the need for more reliable surveillance systems. Routine monitoring of drinking water supplies and recreational waters is performed using fecal indicator microorganisms, such as Escherichia coli , Enterococcus spp., and coliphages. However, the presence and numbers of these indicators, especially E. coli and Enterococcus spp., do not correlate well with those of other pathogens, especially enteric viruses, which are a major cause of waterborne outbreaks associated with contaminated water and food, and recreational use of lakes, ponds, rivers, and estuarine waters. For that reason, there is a growing need for a surveillance system that can detect and quantify viral pathogens directly in water sources to reduce transmission of pathogens associated with fecal transmission. In this review, we present an updated overview of relevant waterborne enteric viruses that we believe should be more commonly screened to better evaluate water quality and to determine the safety of water use and reuse and of epidemiological data on viral outbreaks. We also discuss current methodologies that are available to detect and quantify these viruses in water resources. Finally, we highlight challenges associated with virus monitoring. The information presented in this review is intended to aid in the assessment of human health risks due to contact with water sources, especially since current environmental and adaptive changes may be creating the need for a paradigm shift for indicators of fecal contamination.

Quantitative PCR Detection of Enteric Viruses in Wastewater and Environmental Water Sources by the Lisbon Municipality: A Case Study

Current regulations and legislation require critical revision to determine safety for alternative water sources and water reuse as part of the solution to global water crisis. In order to fulfill those demands, Lisbon municipality decided to start water reuse as part of a sustainable hydric resources management, and there was a need to confirm safety and safeguard for public health for its use in this context. For this purpose, a study was designed that included a total of 88 samples collected from drinking, superficial, underground water, and wastewater at three different treatment stages. Quantitative Polimerase Chain Reaction (PCR) detection (qPCR) of enteric viruses Norovirus (NoV) genogroups I (GI) and II (GII) and Hepatitis A (HepA) was performed, and also FIB (E. coli, enterococci and fecal coliforms) concentrations were assessed. HepA virus was only detected in one untreated influent sample, whereas NoV GI/ NoV GI were detected in untreated wastewater (100/100%), secondary treated effluent (47/73%), and tertiary treated effluent (33/20%). Our study proposes that NoV GI and GII should be further studied to provide the support that they may be suitable indicators for water quality monitoring targeting wastewater treatment efficiency, regardless of the level of treatment.

Occurrence of selected viral and bacterial pathogens and microbiological quality of fresh and frozen strawberries sold in Spain

Strawberry production and exports have been increasing in Spain in recent decades. However, little information is available about their microbiological quality. Due to the growing concern about the microbial safety of these fruits, the objective of this investigation was to study the microbiological quality and the prevalence of the main foodborne pathogens on strawberries sold in Spain. Fresh (n = 152) and frozen (n = 31) samples were obtained from marketplaces and fields in 2017 and 2018. The samples were assayed for total aerobic mesophilic microorganisms (TAM), moulds and yeasts (M&Y), total coliforms (TC), Escherichia coli, Salmonella spp., Listeria monocytogenes as well as Norovirus (NoV) GI and GII. The microbiological counts ranged from <1.70 (detection limit, dl) - 5.89 log₁₀ CFU/g (mean 3.78 log₁₀ CFU/g) for TAM; 2.10-5.86 log₁₀ CFU/g (mean 3.80 log₁₀ CFU/g) for M&Y; and <0.70 (dl) - 4.91 log₁₀ CFU/g (mean 2.15 log₁₀ CFU/g) for TC in fresh strawberries. In frozen strawberries, the counts were <1.70 (dl) - 3.66 log₁₀ CFU/g (mean 2.30 log₁₀ CFU/g) for TAM; <1.70 (dl) - 2.76 log₁₀ CFU/g (mean 1.82 log₁₀ CFU/g) for M&Y; and <0.70(dl) - 1.74 log₁₀ CFU/g (mean 0.77 log₁₀ CFU/g) for TC. All the samples in this study tested negative for Salmonella spp., L. monocytogenes. E. coli and NoV GI and GII genome. A global overview of all the data was executed using Principal Component Analysis (PCA), and the results showed that the scores and loadings according to principal components 1 (PC1) and 2 (PC2) accounted for 75.9% of the total variance, allowing a distinction between fresh and frozen samples. The presence of moulds was significantly higher in the supermarket samples whereas the presence of total coliforms was significantly higher in the field samples (p < 0.05). Although pathogenic microorganisms were not found, preventative measures and prerequisites in the strawberry production chain must be considered in order to avoid possible foodborne diseases related to the microbiological quality of the fruit.

Evaluation of Pre-harvest Microbiological Safety of Blueberry Production With or Without Manure-Derived Fertilizer

Blueberry is an important commodity in Washington State, which was one of the leading blueberry producers in the United States. As a ready-to-eat fruit, blueberry has no or limited post-harvest processing, highlighting an imperative need to evaluate its microbial safety during pre-harvest practice. This study accessed the microbiological safety of blueberry produced in a commercial blueberry field applied with or without manure-derived ammonium sulfate (AS) fertilizer in a 2-year study. Indicator microorganisms of total coliforms and generic E. coli, Shiga toxin-producing Escherichia coli (STEC), Salmonella, and Listeria monocytogenes were monitored in fertilizer, soil, foliar, and blueberry fruit samples by culture methods for each production season. The population of total coliforms in soils was 3.17-3.82 Log10 CFU/g, which was stable throughout the production season and similar between two cropping seasons. Generic E. coli in soils remained at very low levels throughout the 2018 production season. Total coliforms or generic E. coli was not detected in fertilizer, foliar, and blueberry fruit samples collected in both 2017 and 2018 production seasons. STEC and L. monocytogenes were below the detection limit in fertilizer, soil, foliar, and blueberry fruit samples collected in both production seasons. Salmonella was not detected except for soil samples collected pre- and post-fertilizer application in the 2018 cropping season. Collectively, data indicated, under good agricultural practices, blueberry fruits produced in the field with or without manure-derived AS fertilizers had no microbiological safety concern.

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.

Impact of municipal wastewater reuse through micro-irrigation system on the incidence of coliforms in selected vegetable crops

The incidence of coliforms in soil and agricultural produce was evaluated in two vegetable crops, namely, cauliflower and eggplant, which were grown using wastewater for irrigation. Field experiment was conducted at Indian Agricultural Research Institute (IARI), New Delhi, India. In the field experiments to irrigate the crop, municipal wastewater was applied through drip system. The filtration of irrigation water was done through sand media, disk media and their combination. The laterals were placed at surface and subsurface of soil. All filtration processes significantly reduced total coliforms (12-20%) and E. coli (15-25%) populations when evaluated against untreated wastewater. The population dynamics of coliforms in soil profiles indicated that the maximum population of E. coli was estimated on the surface of soil profile when using surface drip, which decreased with soil depth under subsurface placement of drip lateral. After crop harvesting, E. coli in the soil reduced until 20 days after the cessation of irrigation and was highly correlated with soil moisture. E. coli and total coliforms availability were noticed on the surface and in the tissues of leaf and fruit, the coliform count is higher on the surface of plants under surface placement of drip lateral. The concentration of coliforms was lower with eggplant in comparison to cauliflower due to the smooth fruit surface of eggplant. Our study reveals the critical role of subsurface drip irrigation in reducing the load of coliform both in the soil and the crop produce ensuring safety of the consumers against health hazards. In another way protect the environment from wastewater disposal and reduce the burden on synthetic fertilizers as well as shrinking freshwater resources.

Replicating Arabidopsis Model Leaf Surfaces for Phyllosphere Microbiology

Artificial surfaces are commonly used in place of leaves in phyllosphere microbiology to study microbial behaviour on plant leaf surfaces. These surfaces enable a reductionist approach to be undertaken, to enable individual environmental factors influencing microorganisms to be studied. Commonly used artificial surfaces include nutrient agar, isolated leaf cuticles, and reconstituted leaf waxes. Recently, replica surfaces mimicking the complex topography of leaf surfaces for phyllosphere microbiology studies are appearing in literature. Replica leaf surfaces have been produced in agar, epoxy, polystyrene, and polydimethylsiloxane (PDMS). However, none of these protocols are suitable for replicating fragile leaves such as of the model plant Arabidopsis thaliana. This is of importance, as A. thaliana is a model system for molecular plant genetics, molecular plant biology, and microbial ecology. To overcome this limitation, we introduce a versatile replication protocol for replicating fragile leaf surfaces into PDMS. Here we demonstrate the capacity of our replication process using optical microscopy, atomic force microscopy (AFM), and contact angle measurements to compare living and PDMS replica A. thaliana leaf surfaces. To highlight the use of our replica leaf surfaces for phyllosphere microbiology, we visualise bacteria on the replica leaf surfaces in comparison to living leaf surfaces.

Experimental In-Field Transfer and Survival of Escherichia coli from Animal Feces to Romaine Lettuce in Salinas Valley, California

This randomized controlled trial characterized the transfer of E. coli from animal feces and/or furrow water onto adjacent heads of lettuce during foliar irrigation, and the subsequent survival of bacteria on the adaxial surface of lettuce leaves. Two experiments were conducted in Salinas Valley, California: (1) to quantify the transfer of indicator E. coli from chicken and rabbit fecal deposits placed in furrows to surrounding lettuce heads on raised beds, and (2) to quantify the survival of inoculated E. coli on Romaine lettuce over 10 days. E. coli was recovered from 97% (174/180) of lettuce heads to a maximal distance of 162.56 cm (5.33 ft) from feces. Distance from sprinklers to feces, cumulative foliar irrigation, and lettuce being located downwind of the fecal deposit were positively associated, while distance from fecal deposit to lettuce was negatively associated with E. coli transference. E. coli exhibited decimal reduction times of 2.2 and 2.5 days when applied on the adaxial surface of leaves within a chicken or rabbit fecal slurry, respectively. Foliar irrigation can transfer E. coli from feces located in a furrow onto adjacent heads of lettuce, likely due to the kinetic energy of irrigation droplets impacting the fecal surface and/or impacting furrow water contaminated with feces, with the magnitude of E. coli enumerated per head of lettuce influenced by the distance between lettuce and the fecal deposit, cumulative application of foliar irrigation, wind aspect of lettuce relative to feces, and time since final irrigation. Extending the time period between foliar irrigation and harvest, along with a 152.4 cm (5 ft) no-harvest buffer zone when animal fecal material is present, may substantially reduce the level of bacterial contamination on harvested lettuce.

There's a frog in my salad! A review of online media coverage for wild vertebrates found in prepackaged produce in the United States

Prepackaged leafy green vegetables represent one of the fastest growing segments of the fresh-produce industry in the United States. Several steps in the production process have been mechanized to meet the downstream demand for prebagged lettuces. The growth in this market, however, has come with drawbacks, and chief among them are consumers finding wild animals in prepackaged crops. These incidents may signal an overburdened produce supply chain, but we currently lack the information needed to determine if this is a food-safety problem or food-quality concern. Here, we address this gap by reviewing online media coverage of wild vertebrates found in prepackaged produce items by customers in the United States. We discovered 40 independent incidents since 2003 with 95% having occurred during 2008-2018, suggesting that the frequency of incidents may have increased during the last decade. The minority of incidents included wild animals found in organic produce (27.5%), whereas the majority involved conventionally grown crops (72.5%). Most incidents involved amphibians (52.5%) and reptiles (22.5%), while fewer contained mammals (17.5%) and birds (7.5%). Frogs and toads made up all of the amphibian-related incidents, with more than 60% comprising small-bodied treefrogs found in various types of fresh leafy greens. At least seven incidents involved Pacific Treefrogs (Hyliola regilla) and three comprised Green Anoles (Anolis carolinensis). One lizard and nine frogs were found alive, and at least two frogs were released into non-native areas. This is the first review quantifying incidents of vertebrates found by customers in prepackaged produce, yet it remains unclear whether these occurrences indicate a food-safety crisis or a complaint against food quality. Nevertheless, wild animals can spread diseases to humans via contaminated produce, therefore we contend that industry professionals can reduce the potential health risk to their consumers and negative economic consequences to themselves through increased attention to this matter.

Comparison of replica leaf surface materials for phyllosphere microbiology

Artificial surfaces are routinely used instead of leaves to enable a reductionist approach in phyllosphere microbiology, the study of microorganisms residing on plant leaf surfaces. Commonly used artificial surfaces include, flat surfaces, such as metal and nutrient agar, and microstructured surfaces, such as isolate leaf cuticles or reconstituted leaf waxes. However, interest in replica leaf surfaces as an artificial surface is growing, as replica surfaces provide an improved representation of the complex topography of leaf surfaces. To date, leaf surfaces have predominantly been replicated for their superhydrophobic properties. In contrast, in this paper we investigated the potential of agarose, the elastomer polydimethylsiloxane (PDMS), and gelatin as replica leaf surface materials for phyllosphere microbiology studies. Using a test pattern of pillars, we investigated the ability to replicate microstructures into the materials, as well as the degradation characteristics of the materials in environmental conditions. Pillars produced in PDMS were measured to be within 10% of the mold master and remained stable throughout the degradation experiments. In agarose and gelatin the pillars deviated by more than 10% and degraded considerably within 48 hours in environmental conditions. Furthermore, we investigated the surface energy of the materials, an important property of a leaf surface, which influences resource availability and microorganism attachment. We found that the surface energy and bacterial viability on PDMS was comparable to isolated Citrus × aurantium and Populus × canescens leaf cuticles. Hence indicating that PDMS is the most suitable material for replica leaf surfaces. In summary, our experiments highlight the importance of considering the inherent material properties when selecting a replica leaf surface for phyllosphere microbiology studies. As demonstrated, a PDMS replica leaf offers a control surface that can be used for investigating microbe-microbe and microbe-plant interactions in the phyllosphere, which will enable mitigation strategies against pathogens to be developed.

Plant species affects establishment of Escherichia coli O157:H7 gfp+ on leafy vegetables

AIMS

Greenhouse trials were conducted with different cultivars of baby leaf spinach, rocket and Swiss chard and inoculation of Escherichia coli O157:H7 gfp+, to determine whether plant species and cultivar have an impact on the establishment of this strain.

METHODS AND RESULTS

Three cultivars each of spinach, rocket and Swiss chard were spray inoculated with E. coli O157:H7 gfp+ at doses of log 7 CFU per ml. Due to the different lengths of growing period spinach and Swiss chard were spray inoculated three times and rocket five times, with final inoculation performed 3 days prior to harvest. After a growing period of 26-33 days, E. coli O157:H7 gfp+ was recovered from the leaf surface in mean populations between log 1 and 6 CFU per gram. The lowest occurrence of E. coli O157:H7 gfp+ was found on rocket leaves and the highest on spinach. There was no significant difference in the establishment of E. coli O157:H7 gfp+ between cultivars, but there were differences between plant species. Indigenous phyllosphere bacteria were pure cultured and identified with 16S rRNA gene sequencing.

CONCLUSIONS

Despite the same high inoculation dose of E. coli O157:H7 gfp+ on leaves, the establishment rate differed between plant species. However, plant cultivar did not affect establishment. Pantoea agglomerans dominated the identified bacterial isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

As previous studies are inconclusive on choice of model plant species and cultivar, we studied whether plant species or cultivar determines the fate of E. coli O157:H7 gfp+ on leafy vegetables. The findings indicate that plant species is a key determinant in the establishment of E. coli O157:H7 gfp+.

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.

Pre-harvest internalization and surface survival of Salmonella and Escherichia coli O157:H7 sprayed onto different lettuce cultivars under field and growth chamber conditions

Plant genotype has been advocated to have an important role in the fate of enteric pathogens residing in lettuce foliage. This study was therefore undertaken under the premise that different pathogen responses could occur in lettuce cultivars with cultivar selection being one of several hurdles in an overall strategy for controlling foodborne pathogens on field-grown produce. Up to eight lettuce cultivars ('Gabriella', 'Green Star', 'Muir', 'New Red Fire', 'Coastal Star', 'Starfighter', 'Tropicana', and 'Two Star') were examined in these experiments in which the plants were subjected to spray contamination of their foliage with pathogens. In an experiment that addressed internalization of Salmonella, cultivar was determined to be a significant variable (P < 0.05) with 'Gabriella' and 'Muir' being the least and most likely to exhibit internalization of this pathogen, respectively. Furthermore, antimicrobials (total phenols and antioxidant capacity chemicals) could be part of the plant's defenses to resist internalization as there was an inverse relationship between the prevalence of internalization at 1 h and the levels of these antimicrobials (r = -0.75 to -0.80, P = 0.0312 to 0.0165). Internalized cells appeared to be transient residents in that across all cultivars, plants sampled 1 h after being sprayed were 3.5 times more likely to be positive for Salmonella than plants analyzed 24 h after spraying (95% CI from 1.5 to 8.2, P = 0.0035). The fate of surface-resident Salmonella and Escherichia coli O157:H7 was addressed in subsequent growth chamber and field experiments. In the growth chamber study, no effect of cultivar was manifested on the fate of either pathogen when plants were sampled up to 12 days after spray contamination of their foliage. However, in the field study, five days after spraying the plants, Salmonella contamination was significantly affected by cultivar (P < 0.05) and the following order of prevalence of contamination was observed: 'Muir' < 'Gabriella' < 'Green Star' = 'New Red Fire' < 'Coastal Star'. Nine days after spray contamination of plants in the field, no effect of cultivar was exhibited due primarily to the low prevalence of contamination observed for Salmonella (8 of 300 plant samples positive by enrichment culture) and E. coli O157 (4 of 300 plant samples positive by enrichment culture). Given the narrow window of time during which cultivar differences were documented, it is unlikely that cultivar selection could serve as a viable option for reducing the microbiological risk associated with lettuce.

Innovative Nonthermal Technologies: Chlorophyllin and Visible Light Significantly Reduce Microbial Load on Basil

Due to the high amount of biologically active compounds, basil is one of the most popular herbs. However, several outbreaks have been reported in the world due to the consumption of basil contaminated with different food pathogens. The aim of this study is to apply nonthermal and ecologically friendly approach based on photosensitization for microbial control of basil which was naturally contaminated with mesophils and inoculated with thermoresistant food pathogen Listeria monocytogenes 56Ly. The obtained data indicate that soaking the basil in 1.5·10^-4 M chlorophyllin (Chl) for 15 min and illumination with light for 15 min at 405 nm significantly reduced total aerobic microorganisms on basil by 1.3 log CFU/g, and thermoresistant L. monocytogenes 56Ly from 6.1 log CFU/g in control to 4.5 log CFU/g in the treated samples. It is important to note that this treatment had no impact on enzymatic activity of polyphenol oxidase and pectinesterase. Results obtained in this study support the idea that photosensitization technique with its high selectivity, antimicrobial efficiency and nonthermal nature can serve in the future for the development of safe nonthermal and environmentally friendly preservation technology for different fruits and vegetables.

Decontamination and survival of Enterobacteriaceae on shredded iceberg lettuce during storage

Enterobacteriaceae family can contaminate fresh produce at any stage of production either at pre-harvest or post-harvest stages. The objectives of the current study were to i) identify Enterobacteriaceae species on iceberg lettuce, ii) compare the decontamination efficiency of water, sodium hypochlorite (free chlorine 200 ppm), peroxyacetic acid (PA 80 ppm; Kenocid 2100®) or their combinations and ionizing radiation against Enterobacteriaceae on shredded iceberg lettuce and iii) determine the survival of Enterobacteriaceae post-treatment storage of shredded iceberg lettuce at 4, 10 and 25 °C, for up to 7 days. Klebsiella pneumonia spp. pneumonia, Enterobacter cloacae, Klebsiella oxytoca, Pantoea spp., Leclercia adecarboxylata and Kluyvera ascorbate were identified on iceberg lettuce. No significant difference (P≥ 0.05) among Enterobacteriaceae survival after washing with water or sanitizing with sodium hypochlorite or Kenocid 2100® (reduction ≤ 0.6 log CFU/g) were found. Combined sanitizer treatments were more effective against Enterobacteriaceae than single washing/sanitizing treatments. Sanitization of iceberg lettuce with combined washing/sanitizing treatments reduced Enterobacteriaceae by 0.85-2.24 CFU/g. Post-treatment growth of Enterobacteriaceae during storage on samples sanitized with sodium hypochlorite and Kenocid 2100® was more than on samples washed with water. The D10-value of Enterobacteriaceae on shredded iceberg lettuce was 0.21 KGy. The reduction of Enterobacteriaceae populations on iceberg after gamma radiation (0.6 KGy) was 3 log CFU/g, however, Enterobacteriaceae counts increased post-irradiation storage by 4-5 log CFU/g. Therefore, washing shredded iceberg lettuce with combined sanitizing treatment (sodium hypochlorite/sodium hypochlorite, sodium hypochlorite/Kenocid 2100®, or Kenocid 2100®/Kenocid 2100®) for total time of 6 min or exposing it to gamma irradiation (0.6 KGy) can decrease the risk of Enterobacteriaceae (reduction ≥ 2 log). Post-washing storage of sliced iceberg lettuce (4, 10, 25 °C) could increase the risk of Enterobacteriaceae as their counts increased during storage even at low temperatures.

Sources and contamination routes of microbial pathogens to fresh produce during field cultivation: A review

Foodborne illness resulting from the consumption of contaminated fresh produce is a common phenomenon and has severe effects on human health together with severe economic and social impacts. The implications of foodborne diseases associated with fresh produce have urged research into the numerous ways and mechanisms through which pathogens may gain access to produce, thereby compromising microbiological safety. This review provides a background on the various sources and pathways through which pathogenic bacteria contaminate fresh produce; the survival and proliferation of pathogens on fresh produce while growing and potential methods to reduce microbial contamination before harvest. Some of the established bacterial contamination sources include contaminated manure, irrigation water, soil, livestock/ wildlife, and numerous factors influence the incidence, fate, transport, survival and proliferation of pathogens in the wide variety of sources where they are found. Once pathogenic bacteria have been introduced into the growing environment, they can colonize and persist on fresh produce using a variety of mechanisms. Overall, microbiological hazards are significant; therefore, ways to reduce sources of contamination and a deeper understanding of pathogen survival and growth on fresh produce in the field are required to reduce risk to human health and the associated economic consequences.

Attachment of Salmonella enterica on Mangoes and Survival Under Conditions Simulating Commercial Mango Packing House and Importer Facility

Consumption of raw mangoes has led to multiple Salmonella-associated foodborne outbreaks in the United States. Although several studies have investigated the epiphytic fitness of Salmonella on fresh produce, there is sparse information available on the survival of Salmonella on mangoes under commercial handling and storage conditions. Hence, the objective of the study was to evaluate the survival of Salmonella on mangoes under ambient conditions simulating the mango packing house and importer facility. Further, the ability of the pathogen to adhere and attach on to the mango fructoplane was also investigated. For the attachment assays, mango skin sections were inoculated with fifty microliters of S. Newport suspension (6.5 log CFU/skin section) and minimum time required for adhesion and attachment were recorded. With the survival assays, unwaxed mangoes were spot inoculated with the Salmonella cocktail to establish approximately 4 and 6.5 log CFU/mango. The fruits were then subjected to different storage regimens simulating fruit unloading, waxing, and storage at the packing house and ripening and storage at the importer facility. Results of our study reveal that Salmonella was able to adhere on to the fructoplane immediately after contact. Further, formation of attachment structures was seen as early as 2 min following inoculation. With the survival assays, irrespective of the inoculum levels, no significant increase or decrease in pathogen population was observed when fruit were stored either at ambient (29-32°C and RH 85-95%, for 48 h), ripening (20-22°C and RH 90-95% for 9 days) or refrigerated storage (10-15°C and 85-95% for 24-48 h) conditions. Therefore, once contaminated, mangoes could serve as potential vehicles in the transmission of Salmonella along the post-harvest environment. Hence development and adoption of effective food safety measures are warranted to promote the microbiological safety of mangoes.

Salmonella enterica Contamination of Market Fresh Tomatoes: A Review

Salmonella contamination associated with market fresh tomatoes has been problematic for the industry and consumers. A number of outbreaks have occurred, and dollar losses for the industry, including indirect collateral impact to agriculturally connected communities, have run into the hundreds of millions of dollars. This review covers these issues and an array of problems and potential solutions surrounding Salmonella contamination in tomatoes. Some other areas discussed include (i) the use of case-control studies and DNA fingerprinting to identify sources of contamination, (ii) the predilection for contamination based on Salmonella serovar and tomato cultivar, (iii) internalization, survival, and growth of Salmonella in or on tomatoes and the tomato plant, in biofilms, and in niches ancillary to tomato production and processing, (iv) the prevalence of Salmonella in tomatoes, especially in endogenous regions, and potential sources of contamination, and (v) effective and experimental means of decontaminating Salmonella from the surface and stem scar regions of the tomato. Future research should be directed in many of the areas discussed in this review, including determining and eliminating sources of contamination and targeting regions of the country where Salmonella is endemic and contamination is most likely to occur. Agriculturalists, horticulturalists, microbiologists, and epidemiologists may make the largest impact by working together to solve other unanswered questions regarding tomatoes and Salmonella contamination.

Demonstration tests of irrigation water disinfection with chlorine dioxide in open field cultivation of baby spinach

BACKGROUND

Treatments for the disinfection of irrigation water have to be evaluated by demonstration tests carried out under commercial settings taking into account not only their antimicrobial activity but also the potential phytotoxic effects on the crop. The consequences of the treatment of irrigation water with chlorine dioxide (ClO₂ ) used for sprinkler irrigation of baby spinach in two commercial agricultural fields was assessed.

RESULTS

Residual ClO₂ levels at the sprinklers in the treated field were always below 1 mg L^-1 . ClO₂ treatment provoked limited but statistically significant reductions in culturable Escherichia coli counts (0.2-0.3 log reductions), but not in the viable E. coli counts in water, suggesting the presence of viable but non-culturable cells (VBNC). Although disinfected irrigation water did not have an impact on the microbial loads of Enterobacteriaceae nor on the quality characteristics of baby spinach, it caused the accumulation of chlorates (up to 0.99 mg kg^-1 in plants) and the reduction of the photosynthetic efficiency of baby spinach.

CONCLUSION

Low concentrations of ClO₂ are effective in reducing the culturable E. coli present in irrigation water but it might induce the VBNC state. Presence of disinfection by-products and their accumulation in the crop must be considered to adjust doses in order to avoid crop damage and chemical safety risks. © 2017 Society of Chemical Industry.

Disinfection by-products in baby lettuce irrigated with electrolysed water

BACKGROUND

Irrigation water disinfection reduces the microbial load but it might lead to the formation and accumulation of disinfection by-products (DBPs) in the crop. If DBPs are present in the irrigation water, they can accumulate in the crop, particularly after the regrowth, and be affected by the postharvest handling such as washing and storage. To evaluate the potential accumulation of DBPs, baby lettuce was grown using irrigation water treated with electrolysed water (EW) in a commercial greenhouse over three consecutive harvests and regrowths. The impact of postharvest practices such as washing and storage on DBP content was also assessed.

RESULTS

Use of EW caused the accumulation of chlorates in irrigation water (0.02-0.14 mg L-1 ), and in the fresh produce (0.05-0.10 mg kg-1 ). On the other hand, the disinfection treatment had minor impact regarding the presence of trihalomethanes (THMs) in water (0.3-8.7 μg L-1 max), and in baby lettuce (0.3-2.9 μg kg-1 max).

CONCLUSIONS

Disinfection of irrigation water with EW caused the accumulation of chlorates in the crop reaching levels higher than the current maximum residual limit established in the EU legislation for leafy greens. © 2017 Society of Chemical Industry.

Assessment of Salmonella spp. and Escherichia coli O157:H7 growth on lettuce exposed to isothermal and non-isothermal conditions

This study aimed to assess the growth of Salmonella and Escherichia coli O157:H7 on lettuce exposed to isothermal and non-isothermal conditions. Pathogens were inoculated on lettuce separately and stored under isothermal condition at 5 °C, 10 °C, 25 °C, 37 °C for both bacteria, at 40 °C for Salmonella and 42 °C for E. coli O157:H7. Growth curves were built by fitting the data to the Baranyi's DMFit, generating R2 values greater than 0.92 for primary models. Secondary models were fitted with Ratkowsky equations, generating R2 values higher than 0.91 and RMSE lower than 0.1. Experimental data showed that both bacteria could grow at all temperatures. Also, the growth of both pathogens under non-isothermal conditions was studied simulating temperatures found from harvest to supermarkets in Brazil. Models were analysed by R2, RMSE, bias factor (Bf) and accuracy factor (Af). Salmonella and E. coli O157:H7 were able to grow in this temperature profile and the models could predict the behavior of these microorganisms on lettuce under isothermal and non-isothermal conditions. Based on the results, a negligible growth time (ς) was proposed to provide the time which lettuce could be exposed to a specific temperature and do not present an expressive growth of bacteria. The ς was developed based on Baranyi's primary model equation and on growth potential concept. ς is the value of lag phase added of the time necessary to population grow 0.5 log CFU/g. The ς of lettuce exposed to 37 °C was 1.3 h, while at 5 °C was 3.3 days.