Survival Of Enteric Pathogens Research Articles

Identification and characterization of lettuce cultivars with high inhibitory activity against the human pathogen Escherichia coli O157:H7: Toward a plant-intrinsic hurdle approach to microbial safety

Foodborne illness linked to fruit and vegetables poses a major challenge to public health and horticulture production. Processed lettuce has been implicated in recurrent outbreaks of pathogenic Shiga toxin-producing Escherichia coli (STEC) infection. We hypothesized that plant defenses elicited by mechanical injury may effect STEC inhibition in cut leaves. Intact and cut leaves of 31 lettuce cultivars (Lactuca spp.) selected from >500 accessions based on their resistance to common insect pests and the necrotrophic lettuce drop pathogen were assessed for STEC serovar O157:H7 (EcO157) survival under cold storage conditions. The cultivars were previously ranked also for phenotypes such as resistance to other phytopathogens and physiological traits. Total leaf phenolic compounds, anthocyanins, and reactive oxygen species (ROS); and phenylalanine lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO) activity were quantified in each cultivar. Principal Component Analysis (PCA) and K-means cluster analysis were applied to group phenotypes and EcO157 population decline on lettuce. In five cultivars, high resistance to herbivorous insects (aphids, leaf miners and thrips), diseases (lettuce drop, downy mildew, and Impatiens Necrotic Spot Virus), and the disorder tipburn was associated with up to 42-fold EcO157 population decline on cold-stored cut (shredded) leaves, and with up to 11-fold difference in decline on cold-stored intact vs cut leaves (ΔD). The decline on these cold-stored cut cultivars also was up to 24-fold greater than on the cultivar with the lowest decline, and up to 8-fold greater than the mean decline for all 31 cultivars (P < 0.01). Resistance to the hemibiotrophic pathogen causing lettuce bacterial leaf spot, Xanthomonas hortorum pv. vitians, was not indicative of high EcO157 inhibition in this system. High PAL activity, and phenolic and anthocyanin content (PPA); and high PAL and POD activity, were associated with high EcO157 population decline (P < 0.05). One cultivar with high susceptibility to herbivorous insects and phytopathogens, and low levels of defense metabolism nevertheless showed high EcO157 inhibition, suggesting other plant inhibitory characteristics at play. Basal plant immunity and pathways associated with a strong wound response may inform about enteric pathogen survival on minimally processed postharvest lettuce. The related traits identified in this study may serve to breed new genotypes with intrinsically enhanced microbial safety.

Growth Media of Escherichia coli Does Not Affect Its Survival in Soil under Static Conditions

Many studies have examined the survival of Escherichia coli and foodborne pathogens in agricultural soils. The results of these studies can be influenced by various growth conditions and growth media used when preparing cultures for an experiment. The objectives of this study were to (i) determine the growth curves of rifampin (R)-resistant E. coli in three types of growth media containing R: tryptic soy agar (TSA-R); tryptic soy broth (TSB-R); and poultry pellet extract (PPE-R) and (ii) evaluate the influence of growth media on the survival of E. coli in agricultural soil. Poultry pellet extract (PPE) was prepared by filter sterilizing a 1:10 suspension of heat-treated poultry pellets in sterile water. Generic E. coli (TVS 353) acclimated to 80 μg/mL of R was grown in TSA-R, TSB-R, and PPE-R at 3.0 to 3.5 log CFU/mL and incubated at 37°C. Growth curves were determined by quantifying E. coli populations at 0, 4, 8, 16, 24, and 32 h. Soil microcosms were inoculated with E. coli (6.0 log CFU/g) previously cultured in one of the three media types and stored at 25°C, and soil samples were quantified for E. coli on days 0, 1, 3, 7, 14, 28, and 42. Growth curves and survival models were generated by using DMFit and GInaFiT, respectively. E. coli growth rates were 0.88, 0.77, and 0.69 log CFU/mL/h in TSA-R, TSB-R, and PPE-R, respectively. E. coli populations in the stationary phase were greater for cultures grown in TSA-R (9.4 log CFU/mL) and TSB-R (9.1 log CFU/mL) compared with PPE-R (7.9 log CFU/mL). The E. coli populations in the soil remained stable up to 3 days before declining. An approximate 2 log CFU/g decline of E. coli in soil was observed for each culture type between days 3 and 7, after which E. coli populations declined more slowly from days 7 to 42. A biphasic shoulder model was used to evaluate E. coli survival in soils on the basis of growth media. Using standardized culture growth preparation may aid in determining the complex interactions of enteric pathogen survival in soils.

CRP i.e. cAMP receptor protein provides a competitive edge to Salmonella Typhimurium in a microbial community set-up

The survival of enteric pathogens in the multi-nutrient environment involves interaction with other organisms. The fact that competition for nutrient resources has shaped the networking of metabolic pathways is well known. The cAMP receptor protein i.e. CRP is a keystone regulatory protein, connecting various metabolic pathways. Our aim was to study the importance of CRP in nutrient uptake and utilization in Salmonella Typhimurium under intra-species and inter-species nutritive competition. The crp gene knockout (Δcrp) was co-cultured with the wild-type or other pathogens. The Δcrp failed to compete with the wild-type Salmonella Typhimurium, Escherichia coli, Vibrio cholerae and Staphylococcus aureus in nutrient intensive media. However, the survival of the co-cultured Δcrp was unaffected in nutrient-poor media. These results suggest that CRP is necessary for the effective acquisition of readily available nutrients as found in rich media in co-culture. The role of released antimicrobials or surface proteins of the co-cultured strains was also overruled by culturing the mutant in the supernatant of these organisms and separating the cultures in the same media respectively. The co-cultured Δcrp showed an enhanced survival when overall metabolism was reduced with low temperature and antibiotics like chloramphenicol. A circumstantial evidence that CRP manages the global and limits the futile metabolism is provided by this study. The absence of CRP doesn’t affect the survival of the standalone culture. However, the role of this protein becomes obvious in a bacterial community setup. Therefore, CRP is crucial for Salmonella to survive in an intestinal and external environment.

Proportion of Sewage Sludge to Soil Influences the Survival of Salmonella Dublin and Escherichia coli

The survival of enteric pathogens in sewage sludge can lead to their transferral into the soil environment and subsequent contamination of crops and water courses. This, in turn, can increase the potential spread of gastrointestinal disease. This work aims to determine the persistence of several microorganisms, co‐introduced with sewage sludge, when exposed to varying proportions of sewage sludge to soil. Three microcosm‐based studies are established, inoculated with Salmonella Dublin or an environmentally persistent strain of Escherichia coli (quantified periodically over a period of 42 days), or indigenous sewage sludge E. coli (quantified over a period of 56 days). Treatments consist of a mixture containing: 0, 15, 25, 50, 75, and 100% soil or sludge, depending upon the experiment. Each introduced microorganism decline significantly over time, with greater quantities of soil generally instigating greater die‐off particularly in the cases of environmentally persistent E. coli and S. Dublin. However, this relationship is not proportionally related as sludge/soil mixtures show greater declines than pure soil treatments. In contrast, indigenous sewage sludge E. coli has a more consistent decline across all treatments. This indicates that indigenous strains are more resilient and can be indicative of natural behavior. Moreover, the effects of soil‐borne factors on pathogen attenuation are context dependent and non‐linear, possibly arising from the relative spatial distribution of introduced sludge and attendant microbes in soil.

RpoS Affects Gene Expression in Salmonella enterica serovar Typhi Under Early Hyperosmotic Stress.

During the infectious procedure of Salmonella enterica serovar Typhi (S. Typhi), Salmonella would suffer from some severe environmental stresses, such as gastric acid stress, enteric hyperosmotic stress, bile acids stress, and oxidative stress. S. Typhi must regulate the expression of numerous genes through the complex regulatory network to adapt strict stresses. RpoS, which encodes sigma factor σs, was reported to be a very important regulator in the maximal survival of enteric pathogens including S. enterica in the stress conditions. However, the role of RpoS in S. Typhi under early hyperosmotic stress is not clear. In this study, we prepared the RpoS-deleted mutant (△RpoS) and compared the growth of △RpoS and wild-type strain. In addition, we analyzed its global transcription profile under early hyperosmotic stress by a microarray. The results showed that △RpoS grew significantly slower than wild-type strain and 24 genes displayed differential expression between the wild-type strain and ΔRpoS upon 30-min exposure in the high osmolarity. Most of these genes are associated with enzymes of metabolism. Taken together, our study firstly demonstrated that RpoS affects gene expression in S. Typhi under early hyperosmotic stress and may impact the growth of bacteria by regulating bacterial metabolic enzymes.

Impact of mulches and growing season on indicator bacteria survival during lettuce cultivation

In fresh produce production, the use of mulches as ground cover to retain moisture and control weeds is a common agricultural practice, but the influence that various mulches have on enteric pathogen survival and dispersal is unknown. The goal of this study was to assess the impact of different mulching methods on the survival of soil and epiphytic fecal indicator bacteria on organically grown lettuce during different growing seasons. Organically managed lettuce, cultivated with various ground covers — polyethylene plastic, corn-based biodegradable plastic, paper and straw mulch — and bare ground as a no-mulch control, was overhead inoculated with manure-contaminated water containing known levels of generic Escherichia coli and Enterococcus spp. Leaves and soil samples were collected at intervals over a two week period on days 0, 1, 3, 5, 7, 10 and 14, and quantitatively assessed for E. coli, fecal coliforms and Enterococcus spp. Data were analyzed using mixed models with repeated measures and an exponential decline with asymptote survival model. Indicator bacterial concentrations in the lettuce phyllosphere decreased over time under all treatments, with more rapid E. coli declines in the fall than in the spring (p<0.01). Persistence of E. coli in spring was correlated with higher maximum and minimum temperatures in this season, and more regular rainfall. The survival model gave very good fits for the progression of E. coli concentrations in the phyllosphere over time (R2=0.88±0.12). In the spring season, decline rates of E. coli counts were faster (2013 p=0.18; 2014 p<0.005) for the bare ground-cultivated lettuce compared to mulches. In fall 2014, the E. coli decline rate on paper mulch-grown lettuce was higher (p<0.005). Bacteria fluctuated more, and persisted longer, in soil compared to lettuce phyllosphere, and mulch type was a factor for fecal coliform levels (p<0.05), with higher counts retrieved under plastic mulches in all trials, and higher enterococci levels under straw in fall 2014 (p<0.05). This study demonstrates that mulches used in lettuce production may impact the fate of enteric bacteria in soil or on lettuce, most likely in relation to soil moisture retention, and other weather-related factors, such as temperature and rainfall. The data suggest that the time between exposure to a source of enteric bacteria and harvesting of the crop is season dependent, which has implications for determining best harvest times.

Enteric pathogen survival varies substantially in irrigation water from Belgian lettuce producers.

It is accepted that irrigation water is a potential carrier of enteric pathogens, such as Salmonella and E. coli O157:H7 and, therefore, a source for contamination of fresh produce. We tested this by comparing irrigation water samples taken from five different greenhouses in Belgium. The water samples were inoculated with four zoonotic strains, two Salmonella and two E. coli O157:H7 strains, and pathogen survival and growth in the water were monitored up till 14 days. The influence of water temperature and chemical water quality was evaluated, and the survival tests were also performed in water samples from which the resident aquatic microbiota had previously been eliminated by filter sterilization. The pathogen’s survival differed greatly in the different irrigation waters. Three water samples contained nutrients to support important growth of the pathogens, and another enabled weaker growth. However, for all, growth was only observed in the samples that did not contain the resident aquatic microbiota. In the original waters with their specific water biota, pathogen levels declined. The same survival tendencies existed in water of 4 °C and 20 °C, although always more expressed at 20 °C. Low water temperatures resulted in longer pathogen survival. Remarkably, the survival capacity of two E. coli 0157:H7 strains differed, while Salmonella Thompson and Salmonella Typhimurium behaved similarly. The pathogens were also transferred to detached lettuce leaves, while suspended in two of the water samples or in a buffer. The effect of the water sample on the pathogen’s fitness was also reproduced on the leaves when stored at 100% relative humidity. Inoculation of the suspension in buffer or in one of the water samples enabled epiphytic growth and survival, while the pathogen level in the other water sample decreased once loaded on the leaves. Our results show that irrigation waters from different origin may have a different capacity to transmit enteric pathogens and an important impact on the fitness of the pathogens to sustain and even grow on the leaf surface.

Enteric pathogen-plant interactions: molecular connections leading to colonization and growth and implications for food safety.

Leafy green vegetables have been identified as a source of foodborne illnesses worldwide over the past decade. Human enteric pathogens, such as Escherichia coli O157:H7 and Salmonella, have been implicated in numerous food poisoning outbreaks associated with the consumption of fresh produce. An understanding of the mechanisms responsible for the establishment of pathogenic bacteria in or on vegetable plants is critical for understanding and ameliorating this problem as well as ensuring the safety of our food supply. While previous studies have described the growth and survival of enteric pathogens in the environment and also the risk factors associated with the contamination of vegetables, the molecular events involved in the colonization of fresh produce by enteric pathogens are just beginning to be elucidated. This review summarizes recent findings on the interactions of several bacterial pathogens with leafy green vegetables. Changes in gene expression linked to the bacterial attachment and colonization of plant structures are discussed in light of their relevance to plant-microbe interactions. We propose a mechanism for the establishment and association of enteric pathogens with plants and discuss potential strategies to address the problem of foodborne illness linked to the consumption of leafy green vegetables.

Examination of factors for use as potential predictors of human enteric pathogen survival in soil

Three soils that varied in their physicochemical characteristics and microbial diversity were inoculated with Escherichia coli O157:H7 and Salmonella to determine the relative impact of abiotic and biotic factors on the pathogens' survival when the soil was held at 25°C. Three soils that were classified as having low, medium and high microbial diversity were divided into two batches for adjustment to 20% of water-holding capacity and to 40% of water-holding capacity. Soils were inoculated with both green fluorescent-labelled E. coli O157:H7 and red fluorescent-labelled Salmonella (5 log CFU g(-1) dry weight) and held at 25°C. Pathogens inoculated into an acidic soil died off within 9 weeks, whereas they were still detected in the other two soils by enrichment culture after 18 weeks. Moisture did not affect inactivation of E. coli O157:H7, but did affect Salmonella inactivation in soil having the greatest organic load and microbial diversity. Using multiple linear regression analysis, 98.7% of the variability in the inactivation rate for E. coli O157:H7 was explained by a model that included the variables of initial pH and electrical conductivity. Salmonella's inactivation rate was predicted by a model that included pH and initial cell numbers of copiotrophic and oligotrophic bacteria. This study provided evidence of specific properties that impact inactivation of E. coli O157:H7 and Salmonella in soils at 25°C. Identification of factors influential in the die-off of enteric pathogens will assist in developing guidelines for safe intervals between field contamination events and planting or harvesting of fresh-cut produce crops.

Long-term survival of Escherichia coli O157:H7 and Salmonella enterica on butterhead lettuce seeds, and their subsequent survival and growth on the seedlings

The long-term survival of enteric pathogens on butterhead lettuce seeds, and their subsequent survival and growth on seedlings were investigated. Lettuce seeds were inoculated at a high level with two Salmonella enterica and two Escherichia coli O157:H7 strains each (±8log10 CFU/g seed) and the survival of the pathogens was monitored over two years using standard plating techniques on selective medium. The Salmonella strains (serovars Typhimurium and Thompson) survived significantly better on the seeds than the E. coli O157:H7 strains (MB3885 and NCTC12900). When individual seeds were tested two years after inoculation, Salmonella was recovered from each individual seed, whereas E. coli O157:H7 only from 4% to 14% of the seeds, depending on the recovery method. When contaminated stored seeds were germinated and the seedlings examined for presence of the pathogens, it was clear that both pathogens were able to proliferate on the seedlings. Pathogen counts up to 5.92log10 CFU and 4.41log10 CFU per positive seedling were observed for Salmonella and E. coli O157:H7, respectively. Our study not only confirms the long-term survival of enteric pathogens on seeds but also shows that the pathogens maintain their ability to resuscitate and proliferate on the seedlings. Seeds or seedlings should be considered as contamination sources for the cultivation of leafy vegetables such as butterhead lettuce grown in greenhouses.

A reconstruction of Rainfall, Droughts, Nutrients and Algae in a drinking water reservoir near Sydney, Australia

In contrast to studies on (long-term) survival of enteric pathogens in the environment, investigations on the principles of their growth and competition with autochthonous aquatic bacteria are rare and unexplored. Hence, improved basic knowledge is crucial for an adequate risk assessment and for understanding (and avoiding) the spreading of waterborne diseases. Therefore, the pathogen Escherichia coli O157 was grown in competition with a drinking water bacterial community on natural assimilable organic carbon (AOC) originating from diluted wastewater, in both batch and continuous culture. Growth was monitored by flow cytometry enabling enumeration of total cell concentration as well as specific E. coli O157 detection using fluorescently-labelled antibodies. An enhanced competitive fitness of E. coli O157 with higher AOC concentrations, higher temperatures and increased dilution rates (continuous culture) was observed. A classical “opportunist” versus “gleaner” relationship, where E. coli O157 is the “opportunist”, specialised for growth at high nutrient concentrations (μmax: 0.87 h−1 and Ks: 489 μg consumed DOC L−1), and the bacterial community is the “gleaner” adapted to nutrient-poor environments (μmax: 0.33 h−1 and Ks: 7.4 μg consumed DOC L−1) was found. The obtained competition results can be explained by the growth properties of the two competitors determined in pure cultures and it was possible to model many of the observed dynamics based on Monod kinetics. The study provides new insights into the principles governing competition of an enteric pathogen with autochthonous aquatic bacteria.

Competition of Escherichia coli O157 with a drinking water bacterial community at low nutrient concentrations

In contrast to studies on (long-term) survival of enteric pathogens in the environment, investigations on the principles of their growth and competition with autochthonous aquatic bacteria are rare and unexplored. Hence, improved basic knowledge is crucial for an adequate risk assessment and for understanding (and avoiding) the spreading of waterborne diseases. Therefore, the pathogen Escherichia coli O157 was grown in competition with a drinking water bacterial community on natural assimilable organic carbon (AOC) originating from diluted wastewater, in both batch and continuous culture. Growth was monitored by flow cytometry enabling enumeration of total cell concentration as well as specific E. coli O157 detection using fluorescently-labelled antibodies. An enhanced competitive fitness of E. coli O157 with higher AOC concentrations, higher temperatures and increased dilution rates (continuous culture) was observed. A classical “opportunist” versus “gleaner” relationship, where E. coli O157 is the “opportunist”, specialised for growth at high nutrient concentrations (μmax: 0.87 h−1 and Ks: 489 μg consumed DOC L−1), and the bacterial community is the “gleaner” adapted to nutrient-poor environments (μmax: 0.33 h−1 and Ks: 7.4 μg consumed DOC L−1) was found. The obtained competition results can be explained by the growth properties of the two competitors determined in pure cultures and it was possible to model many of the observed dynamics based on Monod kinetics. The study provides new insights into the principles governing competition of an enteric pathogen with autochthonous aquatic bacteria.

Impact of Changes in Sugar Exudate Created by Biological Damage to Tomato Plants on the Persistence of Escherichia coli O157:H7

The survival of enteric pathogens on vegetable leaves improves due to presence of phytopathogens. Phytopathogen damage alters the microenvironment on the leaf surface. The objective of this study was to identify differences in sugar concentrations in tomato leaves damaged by biotropic plant pathogens and determine if these differences affect Escherichia coli O157:H7 survival. E. coli O157:H7 survived better on tomato plants damaged by Xanthomonas campestris than on healthy plants (P = 0.012). The most common sugars and sugar alcohols in the damaged leaf exudate were glucose, fructose, inositol, and sucrose. The abundance of sucrose and inositol differed between the healthy and infected plants (P < 0.05). In this study, it was found that phytopathogen damaged plants increased sugar availability on the leaf surface for E. coli O157:H7 to proliferate. Keeping plants free from biological damage can limit the amount of leaching of sugars that could allow human pathogens to proliferate. There is the possibility of increasing food safety of vegetable products by limiting phytopathogenic damage to plants.

Toxin-Mediated Effects on the Innate Mucosal Defenses: Implications for Enteric Vaccines

Recent studies have confirmed older observations that the enterotoxins enhance enteric bacterial colonization and pathogenicity. How and why this happens remains unknown at this time. It appears that toxins such as the heat-labile enterotoxin (LT) from Escherichia coli can help overcome the innate mucosal barrier as a key step in enteric pathogen survival. We review key observations relevant to the roles of LT and cholera toxin in protective immunity and the effects of these toxins on innate mucosal defenses. We suggest either that toxin-mediated fluid secretion mechanically disrupts the mucus layer or that toxins interfere with innate mucosal defenses by other means. Such a breach gives pathogens access to the enterocyte, leading to binding and pathogenicity by enterotoxigenic E. coli (ETEC) and other organisms. Given the common exposure to LT(+) ETEC by humans visiting or residing in regions of endemicity, barrier disruption should frequently render the gut vulnerable to ETEC and other enteric infections. Conversely, toxin immunity would be expected to block this process by protecting the innate mucosal barrier. Years ago, Peltola et al. (Lancet 338:1285-1289, 1991) observed unexpectedly broad protective effects against LT(+) ETEC and mixed infections when using a toxin-based enteric vaccine. If toxins truly exert barrier-disruptive effects as a key step in pathogenesis, then a return to classic toxin-based vaccine strategies for enteric disease is warranted and can be expected to have unexpectedly broad protective effects.

High Tunnel and Organic Horticulture: Compost, Food Safety, and Crop Quality

High tunnels and protected horticultural structures provide organic and conventional growers with an economic means for extending the harvest season of fresh fruits and vegetables in a wide range of climate zones in North America and elsewhere. This report focuses on benefits associated with high tunnel production of fresh organic produce, including recent data on phytonutrient quality. In addition, this report discusses concerns and knowledge gaps associated with the use of composts and manures relative to food safety of fresh produce and survival of enteric pathogens in the moist, cool, reduced ultraviolet conditions often prevalent in high tunnels during cool-season production. The role of preplant and production elements of Good Agricultural Practices and Good Handling Practices applicable to high tunnel systems is provided.

Survival and Dissemination of Escherichia coli O157:H7 on Physically and Biologically Damaged Lettuce Plants

The ecology of the vegetable leaf surface is important to the survival of enteric pathogens. Understanding changes in ecological parameters during the preharvest stages of production can lead to development of approaches to minimize the hazard of contamination of fresh fruits and vegetables with foodborne pathogens. In this study, survival levels of Escherichia coli O157 over a 10-day period were compared among traumatically injured, phytopathogen-damaged, and healthy lettuce plants. Leaves from lettuce plants cracked along the central vein, plants infected with Xanthomonas campestris pv. vitians, and healthy plants were inoculated with E. coli O157:H7. The presence of E. coli O157:H7 populations on inoculated leaves and non-inoculated leaves of these same plants was determined for 10 days. The density of E. coli O157:H7 decreased over time on the inoculated leaves regardless of the treatment. The population of E. coli O157:H7 remained higher on traumatically injured leaves than on healthy plants (P < 0.001). E. coli O157:H7 was detected on leaves other than the direct inoculation site of the enteric pathogen in all three treatments groups. Preharvest damage, especially that caused by traumatic injury, impacted the survivability of E. coli O157:H7. Maintaining healthy plants and minimizing physical damage around the time of harvest might improve the safety of fresh produce.

Comparative survival of enteric indicators, E. coli and somatic and F-RNA bacteriophages on turf-grass irrigated with recycled water

The aim of this study was to elucidate whether the current withholding period of 4 hours following irrigation of public recreational areas with some classes of recycled water, as prescribed in some Australian state regulations, is valid or whether the holding time can be reduced under specified ambient conditions. A secondary objective was to evaluate laboratory simulations of ambient field conditions for microbial survival experiments. Results suggest that the currently prescribed 4 hour withholding period achieves a reduction of health risk associated with bacterial enteric pathogens that would not otherwise occur if the withholding period was reduced. However, this may not be the case for viral enteric pathogens as the survival of bacteriophages, PRD-1 and MS-2 on turf-grass did not significantly change even after 6 hours, except PRD-1 under high solar conditions. These results suggest that bacteriophages, PRD-1 and MS-2 are more conservative indicators of enteric pathogen survival on UV exposed turf-grass compared with E. coli. The simulations of field conditions in the laboratory were somewhat problematic, with the variations in natural conditions that occur temporally, sometimes for short periods, difficult to reproduce.

Escherichia coli O157:H7 Survival and Growth on Lettuce Is Altered by the Presence of Epiphytic Bacteria

Escherichia coli O157:H7 can survive in low numbers in soil and on plants. Occasionally, conditions may occur in the field that lead to contamination of produce. Survival of enteric pathogens in the field is controlled to a certain extent by complex interactions with indigenous soilborne and seedborne epiphytes. Identifying these interactions may assist in developing strategies to improve produce safety. Two epiphytes were isolated from pathogen-contaminated plants that interact differently with E. coli O157:H7. Wausteria paucula enhanced the survival of E. coli O157:H7 six-fold on lettuce foliage grown from coinoculated lettuce seed. In contrast, Enterobacter asburiae decreased E. coli O157:H7 survival 20- to 30-fold on foliage. Competition also occurred in the rhizosphere and in plant exudate. This competition may be the result of E. asburiae utilization of several of the carbon and nitrogen substrates typically present in exudate and also used by E. coli O157:H7. Hence, competition observed on the plant may involve one or more nutrients provided by the plant. In contrast, a different mechanism may exist between E. coli O157:H7 and W. paucula since commensalism was only observed on foliage, not in the rhizosphere or plant exudate. Good agricultural practices that encourage the growth of competing bacteria, like E. asburiae, may reduce the incidence of produce contamination.

Fitness of Human Enteric Pathogens on Plants and Implications for Food Safety

The continuous rise in the number of outbreaks of foodborne illness linked to fresh fruit and vegetables challenges the notion that enteric pathogens are defined mostly by their ability to colonize the intestinal habitat. This review describes the epidemiology of produce-associated outbreaks of foodborne disease and presents recently acquired knowledge about the behavior of enteric pathogens on plants, with an emphasis on Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes. The growth and survival of enteric pathogens on plants are discussed in the light of knowledge and concepts in plant microbial ecology, including epiphytic fitness, the physicochemical nature of plant surfaces, biofilm formation, and microbe-microbe and plant-microbe interactions. Information regarding the various stresses that affect the survival of enteric pathogens and the molecular events that underlie their interactions in the plant environment provides a good foundation for assessing their role in the infectious dose of the pathogens when contaminated fresh produce is the vehicle of illness.

SURVIVAL OF CAMPYLOBACTER JEJUNI IN MARINATED AND NONMARINATED CHICKEN PRODUCTS

Consumption of chicken products has been increasing. Most of these products in Finland are sold as fresh marinated pieces in consumer packages. The impact of marination on the survival of enteric pathogens is not known. We studied the survival of Campylobacter jejuni on marinated chicken drumsticks and sliced breast strips stored at a refrigerator temperature of +4C. The marinade was an emulsion of vegetable oil and water with spices, NaCl (5.9% wt/wt) and its pH was adjusted to 4.5 with lactic and acetic acid. The survival of C. jejuni was similar in marinated and nonmarinated chicken drumsticks and strips. The organisms were detected for at least nine days at the higher inoculum level (101– 102 CFU/mL) and for at least five days at the lower inoculum level (101– 102 CFU/mL). C. jejuni, inoculated into plain marinade and stored at 4C, was detected after 24 h but not after 48 h. Our results revealed that marination procedure used to reduce and prevent the growth of spoilage organisms does not significantly decrease the survival of Campylobacter jejuni in chicken products.