Ecology ofE. coliO157:H7 andSalmonella entericain the Primary Vegetable Production Chain

Transcriptional and functional responses of Escherichia coli O157:H7 growing in the lettuce rhizoplane

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

Spread and change in stress resistance of Shiga toxin-producing Escherichia coli O157 on fungal colonies

To elucidate the effect of fungal hyphae on the behaviour of Shiga toxin-producing Escherichia coli (STEC) O157, the spread and change in stress resistance of the bacterium were evaluated after coculture with 11 species of food-related fungi including fermentation starters. Spread distances of STEC O157 varied depending on the co-cultured fungal species, and the motile bacterial strain spread for longer distances than the non-motile strain. The population of STEC O157 increased when co-cultured on colonies of nine fungal species but decreased on colonies of Emericella nidulans and Aspergillus ochraceus. Confocal scanning microscopy visualization of green fluorescent protein-tagged STEC O157 on fungal hyphae revealed that the bacterium colonized in the water film that existed on and between hyphae. To investigate the physiological changes in STEC O157 caused by co-culturing with fungi, the bacterium was harvested after 7 days of co-culturing and tested for acid resistance. After co-culture with eight fungal species, STEC O157 showed greater acid resistance compared to those cultured without fungi. Our results indicate that fungal hyphae can spread the contamination of STEC O157 and can also enhance the stress resistance of the bacteria.

Assessments of total and viable Escherichia coli O157:H7 on field and laboratory grown lettuce

Leafy green produce has been associated with numerous outbreaks of foodborne illness caused by strains of Escherichia coli O157:H7. While the amounts of culturable E. coli O157:H7 rapidly decline after introduction onto lettuce in the field, it remains to be determined whether the reduction in cell numbers is due to losses in cell viability, cell injury and a subsequent inability to be detected by standard laboratory culturing methods, or a lack of adherence and hence rapid removal of the organism from the plants during application. To assess which of these options is most relevant for E. coli O157:H7 on leafy green produce, we developed and applied a propidium monoazide (PMA) real-time PCR assay to quantify viable (with PMA) and total (without PMA) E. coli O157:H7 cells on growth chamber and field-grown lettuce. E. coli O157:H7, suspended in 0.1% peptone, was inoculated onto 4-week-old lettuce plants at a level of approximately 10(6) CFU/plant. In the growth chamber at low relative humidity (30%), culturable amounts of the nontoxigenic E. coli O157:H7 strain ATCC 700728 and the virulent strain EC4045 declined 100 to 1000-fold in 24 h. Fewer E. coli O157:H7 cells survived when applied onto plants in droplets with a pipette compared with a fine spray inoculation. Total cells for both strains were equivalent to inoculum levels for 7 days after application, and viable cell quantities determined by PMA real-time PCR were approximately 10(4) greater than found by colony enumeration. Within 2 h after application onto plants in the field, the number of culturable E. coli ATCC 700728 was reduced by up to 1000-fold, whereas PCR-based assessments showed that total cell amounts were equivalent to inoculum levels. These findings show that shortly after inoculation onto plants, the majority of E. coli O157:H7 cells either die or are no longer culturable.

Evaluation of pathogenic Escherichia coli occurrence in vegetable samples from district bazaars in Istanbul using real-time PCR

In this study, a total of 180 vegetable samples collected from several district bazaars of Istanbul were investigated for the occurrence of Escherichia coli using a culture-based method. The isolates were subjected to real-time PCR detection of Shiga-toxin-producing E. coli (STEC) using primers specific for the Shiga toxin (stx1 and stx2) and intimin (eae) virulence genes. The prevalences of E. coli in the samples were 93·3% in spinach, 93·3% in lettuce, 86·6% in parsley, 43·3% in carrot, 33·3% in cucumber and 13·3% in tomato. Of 180 samples, 13 contained STEC (six parsley, three carrots, three lettuces and one cucumber of 30 samples of each). Among 13 STEC-positive isolates, presence of stx1, stx2 and eae was detected in only one sample, stx2 and eae in two samples, and stx2 in ten samples. Serotype O157 was found in parsley, lettuce and carrot; O26 in lettuce, parsley, cucumber and carrot; and O111 and O113 in parsley only. In conclusion, STEC was present in vegetable samples marketed in several district bazaars in Istanbul; this might represent a route of transmission of pathogenic STEC to humans and be harmful to public health.

SIGNIFICANCE AND IMPACT OF THE STUDY

We assessed the occurrence of virulent Escherichia (E.) coli and Shiga-toxin-producing E. coli (STEC) virulent populations in the vegetable samples collected from several district bazaars in Istanbul, Turkey. The results indicated that the vegetables from the bazaars had poor microbial quality and represented a potential health risk to customers.

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

The objective of this study was to determine the effects of farm management and environmental factors on preharvest spinach contamination with generic Escherichia coli as an indicator of fecal contamination. A repeated cross-sectional study was conducted by visiting spinach farms up to four times per growing season over a period of 2 years (2010 to 2011). Spinach samples (n = 955) were collected from 12 spinach farms in Colorado and Texas as representative states of the Western and Southwestern United States, respectively. During each farm visit, farmers were surveyed about farm-related management and environmental factors using a questionnaire. Associations between the prevalence of generic E. coli in spinach and farm-related factors were assessed by using a multivariable logistic regression model including random effects for farm and farm visit. Overall, 6.6% of spinach samples were positive for generic E. coli. Significant risk factors for spinach contamination with generic E. coli were the proximity (within 10 miles) of a poultry farm, the use of pond water for irrigation, a >66-day period since the planting of spinach, farming on fields previously used for grazing, the production of hay before spinach planting, and the farm location in the Southwestern United States. Contamination with generic E. coli was significantly reduced with an irrigation lapse time of >5 days as well as by several factors related to field workers, including the use of portable toilets, training to use portable toilets, and the use of hand-washing stations. To our knowledge, this is the first report of an association between field workers' personal hygiene and produce contamination with generic E. coli at the preharvest level. Collectively, our findings support that practice of good personal hygiene and other good farm management practices may reduce produce contamination with generic E. coli at the preharvest level.

A framework for developing research protocols for evaluation of microbial hazards and controls during production that pertain to the application of untreated soil amendments of animal origin on land used to grow produce that may be consumed raw

Application of manure or soil amendments of animal origin (untreated soil amendments; UTSAs) to agricultural land has been a long-standing practice to maintain or improve soil quality through addition of organic matter, nitrogen, and phosphorus. Much smaller quantities of these types of UTSAs are applied to land used for food crops than to land used for animal grain and forage. UTSAs can harbor zoonotic enteric pathogens that may survive for extended periods after application. Additional studies are needed to enhance our understanding of preharvest microbial food safety hazards and control measures pertaining to the application of UTSAs especially for land used to grow produce that may be consumed raw. This document is intended to provide an approach to study design and a framework for defining the scope and type of data required. This document also provides a tool for evaluating the strength of existing data and thus can aid the produce industry and regulatory authorities in identifying additional research needs. Ultimately, this framework provides a means by which researchers can increase consistency among and between studies and facilitates direct comparison of hazards and efficacy of controls applied to different regions, conditions, and practices.

Consequences of disrupting Salmonella AI-2 signaling on interactions within soft rots

Within soft rots, Salmonella spp. reach population densities 10- to 100-fold higher than within intact plants. The hypothesis that Salmonella spp. exchange AI-2 signals with Pectobacterium carotovorum to increase its competitive fitness was tested using mutants involved in AI-2 production (luxS) or perception (lsrACDBF or lsrG). Co-infections of a wild-type Salmonella sp. and its AI-2 mutants (at ≈3 to 10(4)) were established in green or red tomato ('FL 47' or 'Campari' for 3 or 5 days) as well as tomato co-infected with Pectobacterium (at 10(9)) or its luxS mutant. There were no significant differences in the competitive fitness of Salmonella, indicating that AI-2 signaling is not a major input in the interactions between these organisms under the tested conditions. A Salmonella lsrG::tnpR-lacZ resolvase in vivo expression technology (RIVET) reporter, constructed to monitor AI-2-related gene expression, responded strongly to the luxS deletion but only weakly to external sources of AI-2. Growth in soft rots generally decreased RIVET resolution; however, the effect was not correlated to the luxS genotype of the Pectobacterium sp. The results of this study show that AI-2 signaling offers no significant benefit to Salmonella spp. in this model of colonization of tomato or soft rots.

Organically managed soils reduce internal colonization of tomato plants by Salmonella enterica serovar Typhimurium

A two-phase experiment was conducted twice to investigate the effects of soil management on movement of Salmonella enterica Typhimurium in tomato plants. In the first phase, individual leaflets of 84 tomato plants grown in conventional or organic soils were dip inoculated two to four times before fruiting with either of two Salmonella Typhimurium strains (10(9) CFU/ml; 0.025% [vol/vol] Silwet L-77). Inoculated and adjacent leaflets were tested for Salmonella spp. densities for 30 days after each inoculation. Endophytic bacterial communities were characterized by polymerase chain reaction denaturing gradient gel electrophoresis before and after inoculation. Fruit and seed were examined for Salmonella spp. incidence. In phase 2, extracted seed were planted in conventional soil, and contamination of leaves and fruit of the second generation was checked. More Salmonella spp. survived in inoculated leaves on plants grown in conventional than in organic soil. The soil management effect on Salmonella spp. survival was confirmed for tomato plants grown in two additional pairs of soils. Endophytic bacterial diversities of tomato plants grown in conventional soils were significantly lower than those in organic soils. All contaminated fruit (1%) were from tomato plants grown in conventional soil. Approximately 5% of the seed from infested fruit were internally contaminated. No Salmonella sp. was detected in plants grown from contaminated seed.

Impacts of climate change on the microbial safety of pre-harvest leafy green vegetables as indicated by Escherichia coli O157 and Salmonella spp

The likelihood of leafy green vegetable (LGV) contamination and the associated pathogen growth and survival are strongly related to climatic conditions. Particularly temperature increase and precipitation pattern changes have a close relationship not only with the fate and transport of enteric bacteria, but also with their growth and survival. Using all relevant literature, this study reviews and synthesises major impacts of climate change (temperature increases and precipitation pattern changes) on contamination sources (manure, soil, surface water, sewage and wildlife) and pathways of foodborne pathogens (focussing on Escherichia coli O157 and Salmonella spp.) on pre-harvested LGVs. Whether climate change increases their prevalence depends not only on the resulting local balance of the positive and negative impacts but also on the selected regional climate change scenarios. However, the contamination risks are likely to increase. This review shows the need for quantitative modelling approaches with scenario analyses and additional laboratory experiments. This study gives an extensive overview of the impacts of climate change on the contamination of pre-harvested LGVs and shows that climate change should not be ignored in food safety management and research.

Measuring root disease suppression in response to a compost water extract

Commercial application of compost to prevent plant disease is hindered by variable performance. Here, we describe the use of a growth pouch assay to measure impact of a compost water extract (CWE) on root infection under controlled conditions. Most pea roots (≥95%) inoculated with Fusarium solani or Phoma pinodella spores rapidly develop a single local lesion in the region of elongation. In the presence of CWE, infection of pea roots grown in pouches was reduced by 93 to 100%. CWE used as a drench on pea seedlings grown in sand also resulted in 100% protection but, in a heavy clay soil, infection was reduced by <50%. CWE filtered to remove microorganisms did not inhibit frequency of F. solani infection, and resulted in increased local lesion development on individual roots. CWE inhibited mycelial growth of both pea- and cucumber-infecting isolates of F. solani in culture but exerted <40% protection against cucumber root infection. CWE treatment of pea but not cucumber was associated with retention of a sheath of border cells interspersed with bacteria covering the region of elongation. Growth pouch assays may provide a system to monitor effects of specific compost mixtures on root-rhizosphere interactions, and to identify variables influencing disease control.

Evaluation of animal genetic and physiological factors that affect the prevalence of Escherichia coli O157 in cattle

Controlling the prevalence of Escherichia coli O157 in cattle at the pre-harvest level is critical to reduce outbreaks of this pathogen in humans. Multilayers of factors including the environmental and bacterial factors modulate the colonization and persistence of E. coli O157 in cattle that serve as a reservoir of this pathogen. Here, we report animal factors contributing to the prevalence of E. coli O157 in cattle. We observe the lowest number of E. coli O157 in Brahman breed when compared with other crosses in an Angus-Brahman multibreed herd, and bulls excrete more E. coli O157 than steers in the pens where cattle were housed together. The presence of super-shedders, cattle excreting >10(5) CFU/rectal anal swab, increases the concentration of E. coli O157 in the pens; thereby super-shedders enhance transmission of this pathogen among cattle. Molecular subtyping analysis reveal only one subtype of E. coli O157 in the multibreed herd, indicating the variance in the levels of E. coli O157 in cattle is influenced by animal factors. Furthermore, strain tracking after relocation of the cattle to a commercial feedlot reveals farm-to-farm transmission of E. coli O157, likely via super-shedders. Our results reveal high risk factors in the prevalence of E. coli O157 in cattle whereby animal genetic and physiological factors influence whether this pathogen can persist in cattle at high concentration, providing insights to intervene this pathogen at the pre-harvest level.

Persistence and leaching potential of microorganisms and mineral N in animal manure applied to intact soil columns

Pathogens may reach agricultural soils through application of animal manure and thereby pose a risk of contaminating crops as well as surface and groundwater. Treatment and handling of manure for improved nutrient and odor management may also influence the amount and fate of manure-borne pathogens in the soil. A study was conducted to investigate the leaching potentials of a phage (Salmonella enterica serovar Typhimurium bacteriophage 28B) and two bacteria, Escherichia coli and Enterococcus species, in a liquid fraction of raw pig slurry obtained by solid-liquid separation of this slurry and in this liquid fraction after ozonation, when applied to intact soil columns by subsurface injection. We also compared leaching potentials of surface-applied and subsurface-injected raw slurry. The columns were exposed to irrigation events (3.5-h period at 10 mm h(-1)) after 1, 2, 3, and 4 weeks of incubation with collection of leachate. By the end of incubation, the distribution and survival of microorganisms in the soil of each treatment and in nonirrigated columns with injected raw slurry or liquid fraction were determined. E. coli in the leachates was quantified by both plate counts and quantitative PCR (qPCR) to assess the proportions of culturable and nonculturable (viable and nonviable) cells. Solid-liquid separation of slurry increased the redistribution in soil of contaminants in the liquid fraction compared to raw slurry, and the percent recovery of E. coli and Enterococcus species was higher for the liquid fraction than for raw slurry after the four leaching events. The liquid fraction also resulted in more leaching of all contaminants except Enterococcus species than did raw slurry. Ozonation reduced E. coli leaching only. Injection enhanced the leaching potential of the microorganisms investigated compared to surface application, probably because of a better survival with subsurface injection and a shorter leaching path.

Factors affecting the occurrence of Escherichia coli O157 contamination in irrigation ponds on produce farms in the Suwannee River Watershed

Outbreaks of enteritis caused by Escherichia coli O157 associated with fresh produce have resulted in questions about the safety of irrigation water; however, associated risks have not been systematically evaluated. In this study, the occurrence and distribution of the human pathogen E. coli O157 from vegetable irrigation ponds within the Suwannee River Watershed in Georgia were investigated, and the relationship to environmental factors was analyzed. Surface and subsurface water samples were collected monthly from 10 vegetable irrigation ponds from March 2011 to February 2012. Escherichia coli O157 was isolated from enriched filtrates on CHROMagar and sorbitol MacConkey agar media and confirmed by an agglutination test. Presence of virulence genes stx1, stx2 , and eae was tested by polymerase chain reaction. In addition, 27 environmental variables of the sampled ponds were measured. Denaturing gradient gel electrophoresis was conducted for the analysis of bacterial communities in the water samples. Biserial correlation coefficients were calculated to evaluate the log10 colony-forming unit per millilitre correlations between the environmental factors and the occurrence of E. coli O157. Stepwise and canonical discriminant analyses were used to determine the factors that were associated with the presence and absence of E. coli O157 in water samples. All 10 ponds were positive for E. coli O157 some of the time, mainly in summer and fall of 2011. The temporal distribution of this bacterium differed among the 10 ponds. Temperature, rainfall, populations of fecal coliform, and culturable bacteria were positively correlated with the occurrence of E. coli O157 (P < 0.05), while the total nitrogen concentration, oxidation-reduction potential, and dissolved oxygen concentration were negatively correlated with the occurrence of this pathogen (P < 0.05). Temperature and rainfall were the most important factors contributing to the discrimination between samples with and without E. coli O157, followed by bacterial diversity and culturable bacteria population density. Bacterial numbers and diversity, including fecal coliforms and E. coli O157, increased after rainfall (and possibly runoff from pond margins) in periods with relatively high temperatures, suggesting that prevention of runoff may be important to minimize the risk of enteric pathogens in irrigation ponds.

Risk factors for microbial contamination in fruits and vegetables at the preharvest level: a systematic review

The objective of this study was to perform a systematic review of risk factors for contamination of fruits and vegetables with Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 at the preharvest level. Relevant studies were identified by searching six electronic databases: MEDLINE, EMBASE, CAB Abstracts, AGRIS, AGRICOLA, and FSTA, using the following thesaurus terms: L. monocytogenes, Salmonella, E. coli O157 AND fruit, vegetable. All search terms were exploded to find all related subheadings. To be eligible, studies had to be prospective controlled trials or observational studies at the preharvest level and had to show clear and sufficient information on the process in which the produce was contaminated. Of the 3,463 citations identified, 68 studies fulfilled the eligibility criteria. Most of these studies were on leafy greens and tomatoes. Six studies assessed produce contamination with respect to animal host-related risk factors, and 20 studies assessed contamination with respect to pathogen characteristics. Sixty-two studies assessed the association between produce contamination and factors related to produce, water, and soil, as well as local ecological conditions of the production location. While evaluations of many risk factors for preharvest-level produce contamination have been reported, the quality assessment of the reviewed studies confirmed the existence of solid evidence for only some of them, including growing produce on clay-type soil, the application of contaminated or non-pH-stabilized manure, and the use of spray irrigation with contaminated water, with a particular risk of contamination on the lower leaf surface. In conclusion, synthesis of the reviewed studies suggests that reducing microbial contamination of irrigation water and soil are the most effective targets for the prevention and control of produce contamination. Furthermore, this review provides an inventory of the evaluated risk factors, including those requiring more research.

Gene expression profiling of Escherichia coli in response to interactions with the lettuce rhizosphere

AIMS

The objective of this study was to examine transcriptional changes in Escherichia coli when the bacterium was growing in the lettuce rhizoshpere.

METHODS AND RESULTS

A combination of microarray analyses, colonization assays and confocal microscopy was used to gain a more complete understanding of bacterial genes involved in the colonization and growth of E. coli K12 in the lettuce root rhizosphere using a novel hydroponic assay system. After 3 days of interaction with lettuce roots, E. coli genes involved in protein synthesis, stress responses and attachment were up-regulated. Mutants in curli production (crl, csgA) and flagella synthesis (fliN) had a reduced capacity to attach to roots as determined by bacterial counts and by confocal laser scanning microscopy.

CONCLUSIONS

This study indicates that E. coli K12 has the capability to colonize lettuce roots by using attachment genes and can readily adapt to the rhizosphere of lettuce plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results of this study show curli production and biofilm modulation genes are important for rhizosphere colonization and may provide useful targets to disrupt this process. Further studies using pathogenic strains will provide additional information about lettuce-E. coli interactions.

Adhesion and splash dispersal of Salmonella enterica Typhimurium on tomato leaflets: effects of rdar morphotype and trichome density

Salmonella enterica strains with rdar (red dry and rough) and saw (smooth and white) morphotypes have previously been associated with tomato outbreaks but the dispersal mechanisms of these morphotypes are still poorly understood. In this study, Salmonella adhesion was distinguished from attachment by comparing different contact periods. Initial adhesion of rdar and saw morphotypes of Salmonella was compared in relation to tomato plants with different leaf trichome densities. Trichome densities were increased or reduced by treatment with jasmonic or salicylic acid, respectively. The overall effect of Salmonella morphotype and trichome density on splash dispersal was assessed in a rain simulator and correlated to cell hydrophobicity and initial adhesion. The presence of the rdar morphotype increased initial adhesion at high trichome densities but not at low trichome densities. Attachment of the rdar strain occurred after 30s contact time regardless of trichome density. Splash dispersal was slightly further for the saw morphotype than the rdar morphotype of S. enterica at all trichome densities. Salmonella cells of both morphotypes survived significantly better on the surface of high trichome density leaflets.

Salmonella can reach tomato fruits on plants exposed to aerosols formed by rain

Outbreaks of Salmonella enterica have been associated with tomatoes and traced back to production areas but the spread of Salmonella in agricultural fields is still poorly understood. Post-rain Salmonella transfer from a point source to the air and then to tomato plants was evaluated. GFP-labeled kanamycin-resistant S. enterica serovar Typhimurium (10(8)CFU/mL) with and without expression of the rdar morphotype (rough colonies; cells with fimbriae and cellulose) was used as the point source in the center of a rain simulator. Rain intensities of 60 and 110 mm/h were applied for 5, 10, 20, and 30 min. Petri dishes with lactose broth and tomato plants with fruit (50-80 cm high) were placed in the simulator after the rain had ceased. Salmonella recovery from air was maximum (300 CFU/plate) after a rain episode of 60 mm/h for 10 min at distances of at least 85.5 cm above the source and when the rdar morphotype strain was used. Small scale experiments showed that the smooth-colony strain without fimbriae precipitated from the air in significantly higher numbers than the rdar strain. Transfer of aerial Salmonella with the rdar morphotype to tomato fruits on plants followed a beta distribution (2.5950, 4.7393) within the generalized range from 0 to 30 min of rain. Results show for the first time that Salmonella may transfer from rain to the air and contaminate tomato fruits at levels that could possibly be infectious to humans.

Assessment of root uptake and systemic vine-transport of Salmonella enterica sv. Typhimurium by melon (Cucumis melo) during field production

Among melons, cantaloupes are most frequently implicated in outbreaks and surveillance-based recalls due to Salmonella enterica. There is limited but compelling evidence that associates irrigation water quality as a significant risk of preharvest contamination of melons. However, the potential for root uptake from water and soil and subsequent systemic transport of Salmonella into melon fruit is uncharacterized. The aim of this work was to determine whether root uptake of S. enterica results in systemic transport to fruit at high doses of applied inoculum through sub-surface drip and furrow irrigation during field production of melons. Cantaloupe and honeydew were grown under field conditions, in a silt clay loam soil using standard agronomic practices for California. An attenuated S. enterica sv. Typhimurium strain was applied during furrow irrigation and, in separate plots, buried drip-emitter lines delivered the inoculum directly into the established root zone. Contamination of the water resulted in soil contamination within furrows however Salmonella was not detected on top of the beds or around melon roots of furrow-irrigated rows demonstrating absence of detectable lateral transfer across the soil profile. In contrast, positive detection of the applied isolate occurred in soil and the rhizosphere in drip injected plots; survival of Salmonella was at least 41 days. Despite high populations of the applied bacteria in the rhizosphere, after surface disinfection, internalized Salmonella was not detected in mature melon fruit (n=485). Contamination of the applied Salmonella was detected on the rind surface of melons if fruit developed in contact with soil on the sides of the inoculated furrows. Following an unusual and heavy rain event during fruit maturation, melons collected from the central area of the beds, were shown to harbor the furrow-applied Salmonella. Delivery of Salmonella directly into the peduncle, after minor puncture wounding, resulted in detection of applied Salmonella in the sub-rind tissue below the fruit abscission zone. Results indicate that Salmonella internalization from soil and vascular systemic transport to fruit is unlikely to occur from irrigation water in CA production regions, even if substantially above normal presumptive levels of contamination. Although contaminated irrigation water and subsequently soil in contact with fruit remains a concern for contamination of the external rind, results suggest an acceptable microbial indicator threshold and critical limit for the presence of Salmonella in applied water may be possible by defining appropriate microbiological standards for melon irrigation in California and regions with similar climate, soil texture, and crop management practices.

Electrostatic spraying of food-grade organic and inorganic acids and plant extracts to decontaminate Escherichia coli O157:H7 on spinach and iceberg lettuce

The prevalence of foodborne illnesses is continually on rise. In the U.S.A., Escherichia coli O157:H7 (E. coli) has been associated with several outbreaks in minimally processed foods. Spinach and lettuce pose higher food safety risks and recurring food recalls suggest the insufficiency of current disinfection strategies. We aimed at offering a natural antimicrobial alternative using organic acids (malic, tartaric, and lactic acids [MA, TA, and LA, respectively]) and grape seed extract (GSE) and a novel application method using electrostatic spraying to evenly distribute the antimicrobials onto produce. Spinach and lettuce samples were washed, sanitized with sodium hypochlorite solution (6.25 mL/L), dip inoculated in water containing E. coli (7.0 log CFU/mL) for 24 h, and rewashed with sterile water to remove nonadhered pathogens. The samples were sprayed electrostatically with MA, LA, and GSE alone and in combinations and for comparison, with phosphoric acid (PA) and pH controls with deionized water adjusted to 1.5/2.3/3.6 and stored at 4 °C. When combined with LA (3%), MA (3%) showed 2.1 to 4.0 log CFU/g reduction of E. coli between the days 1 and 14 on spinach and 1.1 to 2.5 log CFU/g reduction on lettuce. Treatment with PA (1.5%) and PA (1.5%)-GSE (2%) exhibited 1.1 to 2.1 log CFU/g inhibition of E. coli on spinach during the 14-d storage. Our findings demonstrated the efficacy of electrostatic spraying of MA, LA, and GSE on fresh produce to improve the safety and lower the public health burden linked to produce contamination.

PRACTICAL APPLICATION

Electrostatic spraying is an emerging technique that can be adopted to improve the distribution and application of antimicrobials during fresh produce sanitation. Relatively simple and quick, the process can access most/all parts of produce surface and offer protection from food pathogens. The use of malic and lactic acids with or without grape seed extract can serve as effective antimicrobials when sprayed electrostatically, lowering the risk from postcontamination issues with spinach and iceberg lettuce. This application technology can be extended to improve the commercial food safety of other produce, fruits, poultry, and meat.

Role of bacteriophage-encoded exotoxins in the evolution of bacterial pathogens

Recent advances in metagenomics research have generated a bounty of information that provides insight into the dynamic genetic exchange occurring between bacteriophage (phage) and their bacterial hosts. Metagenomic studies of the microbiomes from a variety of environments have shown that many of the genes sequenced are of phage origin. Among these genes are phage-encoded exotoxin genes. When phage that carry these genes infect an appropriate bacterial host, the bacterium undergoes lysogenic conversion, converting the bacterium from an avirulent strain to a pathogen that can cause human disease. Transfer of the exotoxin genes between bacteria has been shown to occur in marine environments, animal and human intestines and sewage treatment plants. Surprisingly, phage that encode exotoxin genes are commonly found in environments that lack the cognate bacteria commonly associated with the specific toxin-mediated disease and have been found to be associated with alternative environmental bacterial hosts. These findings suggest that the exotoxin genes may play a beneficial role for the bacterial host in nature, and that this environmental reservoir of exotoxin genes may play a role in the evolution of new bacterial pathogens.

Comparative examination of Escherichia coli O157:H7 survival on romaine lettuce and in soil at two independent experimental sites

Little is known about the influence of abiotic factors such as climate and soil chemistry on the survival of Escherichia coli O157:H7 in field lettuce. We applied a nalidixic acid-resistant derivative of strain ATCC 700728 to field-grown romaine lettuce in two regions in Canada characterized by large variances in soil type and climate. Surviving populations in soil and on lettuce leaves were estimated on sorbitol MacConkey agar supplemented with nalidixic acid. Data were fitted with the Weibull decline function to permit comparison of decay rates in the two experimental sites. E. coli O157:H7 populations fell from 10⁵ to <10² CFU/g on leaves, and <10³ CFU/g in soil within 7 days after inoculation. Analysis revealed there was no significant difference between decay rates at the two experimental sites in either environment. The results of this study suggest that the inherent ecological fitness of E. coli O157:H7 ATCC 700728 determines the extent of survival in the production environment.

Dispersal of Salmonella Typhimurium by rain splash onto tomato plants

Outbreaks of Salmonella enterica have increasingly been associated with tomatoes and traced back to production areas, but the spread of Salmonella from a point source onto plants has not been described. Splash dispersal by rain could be one means of dissemination. Green fluorescent protein-labeled, kanamycin-resistant Salmonella enterica sv. Typhimurium dispensed on the surface of plastic mulch, organic mulch, or soil at 10⁸ CFU/cm² was used as the point source in the center of a rain simulator. Tomato plants in soil with and without plastic or organic mulch were placed around the point source, and rain intensities of 60 and 110 mm/h were applied for 5, 10, 20, and 30 min. Dispersal of Salmonella followed a negative exponential model with a half distance of 3 cm at 110 mm/h. Dispersed Salmonella survived for 3 days on tomato leaflets, with a total decline of 5 log and an initial decimal reduction time of 10 h. Recovery of dispersed Salmonella from plants at the maximum observed distance ranged from 3 CFU/g of leaflet after a rain episode of 110 mm/h for 10 min on soil to 117 CFU/g of leaflet on plastic mulch. Dispersal of Salmonella on plants with and without mulch was significantly enhanced by increasing rain duration from 0 to 10 min, but dispersal was reduced when rainfall duration increased from 10 to 30 min. Salmonella may be dispersed by rain to contaminate tomato plants in the field, especially during rain events of 10 min and when plastic mulch is used.

Distribution and Genetic Diversity of Salmonella enterica in the Upper Suwannee River

The Suwannee River spans the Florida/Georgia border to the Gulf of Mexico, and contributes to regional irrigation and recreational activities. Association of Salmonella enterica with these resources may result in the contamination of produce and disease outbreaks. Therefore, surface water was examined for the distribution of S. enterica at multiple time points from 4 sites on the upper Suwannee River. Isolates were confirmed by detection of the invA gene, and 96% of all samples were positive for the bacterium. Most probable number enumeration ranged from <18 to 5400 MPN/100 mL. Genetic diversity of these isolates (n=110) was compared to other environmental (n=47) or clinical (n=28) strains and to an online library (n=314) using DiversiLab rep-PCR. All strains showed >60% similarity and distributed into 16 rep-PCR genogroups. Most (74%) of the Suwannee River isolates were clustered into two genogroups that were comprised almost exclusively (97%) of just these isolates. Conversely, 85% of the clinical reference strains clustered into other genogroups. However, some Suwannee River isolates (12%) were clustered with these primarily clinically-associated genogroups, supporting the hypothesis that river water can serve as a disease reservoir and that pathogenic strains may persist or possibly originate from environmental sources.

Slicing under chlorinated water improves the disinfection of fresh-cut romaine lettuce

The aim of this study was to determine whether the timing or mode of application influences the antimicrobial efficacy of a sodium hypochlorite solution against microorganisms on fresh-cut Romaine lettuce. Lettuce leaves were treated with a solution of sodium hypochlorite containing 70 mg liter(-1) free chlorine prior to slicing (WLS), while submerged in the solution (CWS), or after slicing (PCS), the last being common practice in the fresh-cut industry. Immediate antimicrobial effects were determined from analyses performed directly after treatment, while delayed effects were derived from analysis of packaged samples stored at 4 and 15°C. Experiments were performed with both uninoculated and inoculated whole leaves, using Escherichia coli O157:H7 from a type collection as an inoculum. The CWS treatment provided the greatest initial reductions in aerobic plate counts of E. coli O157:H7 populations, followed by PCS and WLS. The advantage afforded by the CWS approach was maintained over 10 days in storage at 4°C. In addition, it was noted that the visual quality attributes of the fresh-cut lettuce from the CWS approach were better than those from the other two treatments. These results collectively suggest that slicing lettuce under a sanitizer solution could provide better disinfection of fresh-cut Romaine lettuce than the current practice of washing with sanitizer after cutting has taken place.

Induction of viable but nonculturable Escherichia coli O157:H7 in the phyllosphere of lettuce: a food safety risk factor

Escherichia coli O157:H7 continues to be an important human pathogen and has been increasingly linked to food-borne illness associated with fresh produce, particularly leafy greens. The aim of this work was to investigate the fate of E. coli O157:H7 on the phyllosphere of lettuce under low temperature and to evaluate the potential hazard of viable but nonculturable (VBNC) cells induced under such stressful conditions. First, we studied the survival of six bacterial strains following prolonged storage in water at low temperature (4°C) and selected two strains with different nonculturable responses for the construction of E. coli O157:H7 Tn7gfp transformants in order to quantitatively assess the occurrence of human pathogens on the plant surface. Under a suboptimal growth temperature (16°C), both E. coli O157:H7 strains maintained culturability on lettuce leaves, but under more stressful conditions (8°C), the bacterial populations evolved toward the VBNC state. The strain-dependent nonculturable response was more evident in the experiments with different inoculum doses (10(9) and 10(6) E. coli O157:H7 bacteria per g of leaf) when strain BRMSID 188 lost culturability after 15 days and strain ATCC 43895 lost culturability within 7 days, regardless of the inoculum dose. However, the number of cells entering the VBNC state in high-cell-density inoculum (approximately 55%) was lower than in low-cell-density inoculum (approximately 70%). We recorded the presence of verotoxin for 3 days in samples that contained a VBNC population of 4 to 5 log(10) cells but did not detect culturable cells. These findings indicate that E. coli O157:H7 VBNC cells are induced on lettuce plants, and this may have implications regarding food safety.

A rapid procedure for the detection and isolation of enterohaemorrhagic Escherichia coli (EHEC) serogroup O26, O103, O111, O118, O121, O145 and O157 strains and the aggregative EHEC O104:H4 strain from ready-to-eat vegetables

Human infections with Enterohaemorrhagic Escherichia coli strains (EHEC) as agents of Haemorrhagic Colitis (HC) and Haemolytic Uraemic Syndrome (HUS) are frequently associated with the consumption of EHEC contaminated foodstuffs of different origins. EHEC O26, O103, O111, O118, O121, O145 and O157 strains are responsible for the majority of HC and HUS cases worldwide. In May 2011, the emerging aggregative EHEC O104:H4 strain caused a large outbreak with high HUS incidence in northern Germany. Contaminated sprouted seeds were suspected to be the vehicles of transmission. The examination of vegetables retailed for raw consumption revealed low numbers of E. coli (<100 cfu/g) together with high titres of Enterobacteriaceae and Pseudomonas (approx. 5.6 × 10⁷ cfu/g). Specific methods of EHEC detection adapted to vegetables are not yet published. Therefore, we have developed a rapid and sensitive method for detecting low EHEC contamination in vegetables (1-10 cfu/25 g) with artificially EHEC contaminated ready-to-eat salads. A 6-hour enrichment period in BRILA-broth was sufficient to detect 1-10 EHEC from spiked samples after plating 0.1 ml portions of enrichment culture on selective TBX-agar and CHROMagar STEC plates that were incubated at 44 °C overnight. Unlike EHEC strains, the growth of bacteria of the plant flora was substantially inhibited at 44 °C. DNA for real-time PCR detection of EHEC characteristic genes (stx(1), stx(2), eae, ehxA, and O-antigen associated) was prepared with bacteria grown on TBX-agar plates. The storage of EHEC inoculated salad samples for 72 h at 6 °C resulted in a significant reduction (mean value 14.6%) of detectable EHEC, suggesting interference of EHEC with the resident plant microflora. CHROMagar STEC was evaluated as a selective medium for the detection of EHEC strains. Growth on CHROMagar STEC was closely associated with EHEC O26:[H11], O111:[H8], O118:H16, O121:[H19], O145:[H28], O157:[H7] and aggregative EHEC O104:H4 strains and with the presence of the terB gene (tellurite resistance). TerB sequences were found in 87.2% of 235 EHEC but only in only 12.5% of 567 non-EHEC strains. EHEC strains which did not grow on CHROMagar STEC were negative for terB as frequently observed with EHEC O103:H2 (52.9%) and sorbitol-fermenting O157:NM strains (100%). The enrichment and detection method was applied in the examination of sprouted seeds incriminated as vehicles in the EHEC O104:H4 outbreak in Germany. Aggregative EHEC O104:H4 could be detected and isolated from a sample of sprouted seeds which was suspected as vector of transmission of EHEC O104 to humans.

Inhibition of verocytotoxigenic Escherichia coli by antimicrobial peptides caseicin A and B and the factors affecting their antimicrobial activities

The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n=11), other bacterial pathogenic and spoilage bacteria (n=7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log(10) cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p>0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p>0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥2 mg/ml did not significantly (p>0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.

Variability of Escherichia coli O157 strain survival in manure-amended soil in relation to strain origin, virulence profile, and carbon nutrition profile

The variation in manure-amended soil survival capability among 18 Escherichia coli O157 strains (8 animal, 1 food, and 9 human isolates) was studied using a single sandy soil sample and a single sample of cattle manure as the inoculum carrier. The virulence profiles of E. coli O157 strains were characterized by detection of virulence determinants (73 genes, 122 probes in duplicate) by using the Identibac E. coli genotyping DNA miniaturized microarray. Metabolic profiling was done by subjecting all strains to the Biolog phenotypic carbon microarray. Survival times (calculated as days needed to reach the detection limit using the Weibull model) ranged from 47 to 266 days (median, 120 days). Survival time was significantly higher for the group of human isolates (median, 211 days; minimum [min.], 71; maximum [max.], 266) compared to the group of animal isolates (median, 70 days; min., 47; max., 249) (P = 0.025). Although clustering of human versus animal strains was observed based on pulsed-field gel electrophoresis (PFGE) patterns, no relation between survival time and the presence of virulence genes was observed. Principal component analysis on the metabolic profiling data revealed distinct clustering of short- and long-surviving strains. The oxidization rate of propionic acid, α-ketobutyric acid, and α-hydroxybutyric acid was significantly higher for the long-surviving strains than for the short-surviving strains. The oxidative capacity of E. coli O157 strains may be regarded as a phenotypic marker for enhanced survival in manure-amended soil. The large variation observed in survival is of importance for risk assessment models.

Pathogenic potential of Salmonella Typhimurium DT104 following sequential passage through soil, packaged fresh-cut lettuce and a model gastrointestinal tract

From a quantitative microbial risk assessment perspective it is important to know whether certain food environments influence the pathogenic potential of pathogens and to what extent. The purpose of the present study was to examine the pathogenic potential of S. Typhimurium DT104, measured as the capability to survive a simulated gastrointestinal tract system and the capability of adhering to and invading differentiated Caco-2 cells, after sequential incubation (without intermediate culturing) into soil, lettuce and cut lettuce stored under modified atmosphere (MAP) conditions. Two S. Typhimurium DT104 strains were used, one isolated from a pig carcass and one isolated from lettuce. The most important result of the present study is that the sequential incubation of S. Typhimurium in soil and lettuce slightly increased the capability of surviving the simulated gastric fluid, increased the capability to grow in the simulated intestinal fluid but decreased the capability of epithelial attachment and invasion and decreased the overall survival probability of the gastrointestinal tract system. Some variation in responses between the strains was observed, with the lettuce strain maintaining higher epithelial attachment capability and the carcass strains maintaining higher epithelial invasion capability. This study provided quantitative data on the effect of environmental and food matrices on the pathogenic potential of S. Typhimurium DT104 using a realistic system of sequential incubations in environmental and food matrices, followed by simulated gastrointestinal tract passage without intermediate culturing. These results could aid the development of more realistic quantitative microbial risk assessments.

Persistence of Escherichia coli O157:H7 and its mutants in soils

The persistence of Shiga toxin-producing E. coli O157:H7 in the environment poses a serious threat to public health. However, the role of Shiga toxins and other virulence factors in the survival of E. coli O157:H7 is poorly defined. The aim of this study was to determine if the virulence factors, stx₁, stx₂, stx₁₋₂, and eae in E. coli O157:H7 EDL933 play any significant role in the growth of this pathogen in rich media and in soils. Isogenic deletion mutants that were missing one of four virulence factors, stx₁, stx₂, stx₁₋₂, and eae in E. coli O157:H7 EDL933 were constructed, and their growth in rich media and survival in soils with distinct texture and chemistry were characterized. The survival data were successfully analyzed using Double Weibull model, and the modeling parameters of the mutant strains were not significantly different from those of the wild type. The calculated T(d) (time needed to reach the detection limit, 100 CFU/g soil) for loamy sand, sandy loam, and silty clay was 32, 80, and 110 days, respectively. It was also found that T(d) was positively correlated with soil structure (e.g. clay content), and soil chemistry (e.g. total nitrogen, total carbon, and water extractable organic carbon). The results of this study showed that the possession of Shiga toxins and intimin in E. coli O157:H7 might not play any important role in its survival in soils. The double deletion mutant of E. coli O157:H7 (stx₁⁻stx₂⁻) may be a good substitute to use for the investigation of transport, fate, and survival of E. coli O157:H7 in the environment where the use of pathogenic strains are prohibited by law since the mutants showed the same characteristics in both culture media and environmental samples.

Distribution of Salmonella typhimurium in romaine lettuce leaves

Leafy greens are occasionally involved in outbreaks of enteric pathogens. In order to control the plant contamination it is necessary to understand the factors that influence enteric pathogen-plant interactions. Attachment of Salmonella enterica serovar typhimurium to lettuce leaves has been demonstrated before; however, only limited information is available regarding the localization and distribution of immigrant Salmonella on the leaf surface. To extend our knowledge regarding initial pathogen-leaf interactions, the distribution of green-fluorescent protein-labeled Salmonella typhimurium on artificially contaminated romaine lettuce leaves was analyzed. We demonstrate that attachment of Salmonella to different leaf regions is highly variable; yet a higher attachment level was observed on leaf regions localized close to the petiole (7.7 log CFU g(-1)) compared to surfaces at the far-end region of the leaf blade (6.2 log CFU g(-1)). Attachment to surfaces located at a central leaf region demonstrated intermediate attachment level (7.0 log CFU g(-1)). Salmonella displayed higher affinity toward the abaxial side compared to the adaxial side of the same leaf region. Rarely, Salmonella cells were also visualized underneath stomata within the parenchymal tissue, supporting the notion that this pathogen can also internalize romaine lettuce leaves. Comparison of attachment to leaves of different ages showed that Salmonella displayed higher affinity to older compared to younger leaves (1.5 log). Scanning electron microscopy revealed a more complex topography on the surface of older leaves, as well as on the abaxial side of the examined leaf tissue supporting the notion that a higher attachment level might be correlated with a more composite leaf landscape. Our findings indicate that initial attachment of Salmonella to romaine lettuce leaf depends on multiple plant factors pertaining to the specific localization on the leaf tissue and to the developmental stage of the leaf.

General suppression of Escherichia coli O157:H7 in sand-based dairy livestock bedding

Sand bedding material is frequently used in dairy operations to reduce the occurrence of mastitis and enhance cow comfort. One objective of this work was to determine if sand-based bedding also supported the microbiologically based suppression of an introduced bacterial pathogen. Bedding samples were collected in summer, fall, and winter from various locations within a dairy operation and tested for their ability to suppress introduced populations of Escherichia coli O157:H7. All sources of bedding displayed a heat-sensitive suppressiveness to the pathogen. Differences in suppressiveness were also noted between different samples at room temperature. At just 1 day postinoculation (dpi), the recycled sand bedding catalyzed up to a 1,000-fold reduction in E. coli counts, typically 10-fold greater than the reduction achieved with other substrates, depending on the sampling date. All bedding substrates were able to reduce E. coli populations by over 10,000-fold within 7 to 15 dpi, regardless of sampling date. Terminal restriction fragment length polymorphism (T-RFLP) analysis was used to identify bacterial populations potentially associated with the noted suppression of E. coli O157:H7 in sand bedding. Eleven terminal restriction fragments (TRFs) were overrepresented in paired comparisons of suppressive and nonsuppressive specimens at multiple sampling points, indicating that they may represent environmentally stable populations of pathogen-suppressing bacteria. Cloning and sequencing of these TRFs indicated that they represent a diverse subset of bacteria, belonging to the Cytophaga-Flexibacter-Bacteroidetes, Gammaproteobacteria, and Firmicutes, only a few of which have previously been identified in livestock manure. Such data indicate that microbial suppression may be harnessed to develop new options for mitigating the risk and dispersal of zoonotic bacterial pathogens on dairy farms.

Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism's survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.

Infectious colitis

PURPOSE OF REVIEW

The incidence of gastrointestinal infections continues to increase and infectious colitis contributes to significant morbidity and mortality worldwide. The purpose of this review is to highlight the recent advances in knowledge of pathogens causing infectious colitis. We describe the various pathogens and specifically focus on enterohemorrhagic Escherichia coli (EHEC) O157:H7, Salmonella, Shigella, Campylobacter, and Entamoeba histolytica infections, and their impact on long-term effects, including postinfectious irritable bowel syndrome and inflammatory bowel disease.

RECENT FINDINGS

Salmonella, Campylobacter, and EHEC outbreaks continue to occur with disturbing regularity. Peanut butter and peppers were recently responsible for outbreaks of nontyphoid Salmonella. Recent research has identified Salmonella genes required for colonization of various hosts and transposon-mediated differential hybridization was recently used to identify genes required during infection in different animal models. A number of other strains of EHEC in addition to O157:H7 are emerging as serious threats to food safety in the USA. Campylobacter jejuni isolates are of interest because of absence of genes encoding for classical enterotoxins, and lack of plasmids encoding genes promoting bacterial invasion. Recent research has identified that the organism is able to invade and replicate in infected epithelia via Toll-like receptor (TLR)-2 and TLR-4. Also patients with infectious colitis, in particular Salmonella and Campylobacter, are at increased risk of postinfectious irritable bowel syndrome and inflammatory bowel disease on long-term follow-up. The paradigm of Entamoeba histolytica infection is changing with recent reports of detection of E. dispar deoxyribonucleic acid sequences, previously considered nonpathogenic.

SUMMARY

There has been an explosion in the understanding of the epidemiology, pathobiology, and mechanisms underlying infectious colitis. Additional studies to address prevention strategies and strict screening modalities for these infections are necessary.

Development and implementation of a system for the early identification of emerging risks in food and feed

According to EFSA's Founding Regulation, the Authority is required to "undertake action to identify and characterise emerging risks" in the field of food and feed safety. EFSA provides scientific advice to the risk manager, at both European and Member State level, for the identification of risks present in the food chain. In the area of currently unrecognised but potentially significant risks for public health, EFSA has set up a dedicated unit on emerging risks (EMRISK). Through the identification of drivers of emerging risks, EFSA also intends to anticipate future risks derived from changes in current food/feed production practices or factors impinging on food/feed production or changes in human exposure through food consumption. EFSA aims to establish a data monitoring capacity, data filtering methodology and networking structures to identify emerging risks and drivers of emerging risks in a timely fashion and to communicate these to the risk manager. To date, the first step of this process (data monitoring) is in place. The following steps, that is, filtering and communication, are being rapidly established. Whilst the current data sources monitored are limited, they have been sufficient to enable the elaboration of the procedures for the next steps in the emerging risks identification process. As more data sources become accessible, the process will become more effective. All processes should be in place by mid -2010 and reported on in EFSA's first annual report on emerging risks in 2011. By the end of the second year of operation (2012), the soundness and utility of this approach will be given an initial review.

Quantitative microbial risk assessment for Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in leafy green vegetables consumed at salad bars, based on modeling supply chain logistics

Quantitative microbial risk assessments do not usually account for the planning and ordering mechanisms (logistics) of a food supply chain. These mechanisms and consumer demand determine the storage and delay times of products. The aim of this study was to quantitatively assess the difference between simulating supply chain logistics (MOD) and assuming fixed storage times (FIX) in microbial risk estimation for the supply chain of fresh-cut leafy green vegetables destined for working-canteen salad bars. The results of the FIX model were previously published (E. Franz, S. O. Tromp, H. Rijgersberg, and H. J. van der Fels-Klerx, J. Food Prot. 73:274-285, 2010). Pathogen growth was modeled using stochastic discrete-event simulation of the applied logistics concept. The public health effects were assessed by conducting an exposure assessment and risk characterization. The relative growths of Escherichia coli O157 (17%) and Salmonella enterica (15%) were identical in the MOD and FIX models. In contrast, the relative growth of Listeria monocytogenes was considerably higher in the MOD model (1,156%) than in the FIX model (194%). The probability of L. monocytogenes infection in The Netherlands was higher in the MOD model (5.18×10(-8)) than in the FIX model (1.23×10(-8)). The risk of listeriosis-induced fetal mortality in the perinatal population increased from 1.24×10(-4) (FIX) to 1.66×10(-4) (MOD). Modeling the probabilistic nature of supply chain logistics is of additional value for microbial risk assessments regarding psychrotrophic pathogens in food products for which time and temperature are the postharvest preventive measures in guaranteeing food safety.

Transfer of enteric pathogens to successive habitats as part of microbial cycles

Escherichia coli O157:H7 gfp and Salmonella enterica Typhimurium gfp passed through six successive habitats within a microbial cycle. Pathogen cultures were introduced into cow dung or fodder. Microscopically observed cells and CFUs were monitored in fodder, dung, dung-soil mix, rhizosphere and phyllosphere of cress or oat plants grown in infested dung-soil mix, and in excrements of snails or mice fed with contaminated cress or oat shoots. Both methods were sensitive enough to monitor cells and CFUs throughout the chain. There was a positive correlation between cells and CFUs. Both pathogens declined through the successive habitats, but with unexpected increased densities on plants compared to dung-soil mix. Pathogen densities were higher in the phyllosphere than the rhizosphere of cress, but for oat plants this was reverse. Survival in dung was better after passage through the digestive tract of cows than after introduction of cultures into dung. Positive correlations between pathogens and copiotrophic bacteria (CB) and dissolved organic carbon (DOC) were observed in dung and dung-soil mixtures, but at low DOC contents CB densities were higher than pathogen densities. Thus, the pathogens are able to cycle through different habitats, surviving or growing better at high DOC concentrations, but maintaining population densities that are sufficiently high to cause disease in humans.