Efficacy of Acetic Acid or Chitosan for Reducing the Prevalence of Salmonella- and Escherichia coli O157:H7-Contaminated Leafy Green Plants in Field Systems.

Outbreaks associated with fresh-cut leafy greens continue to occur despite efforts to implement horticultural practices that minimize introduction of enteric pathogens to the crop. The experimental trials in this study were designed to examine the efficacy of an acetic acid (AA)- and chitosan-based spray treatment, applied 1 day prior to harvest, for reducing the prevalence of Escherichia coli O157:H7 (O157) and Salmonella in field-grown leafy greens contaminated at levels detectable only through enrichment culture. Responses to the treatment solution were variable and depended on the type of leafy green (leafy lettuce, spinach, or cabbage), cultivar, pathogen, and AA concentration (0.3 to 0.7%). No significant differences in E. coli O157 prevalence were found for untreated and treated cabbage heads and spinach plants (P > 0.05). In contrast, treatment significantly affected Salmonella on 'Bravo F1' green cabbage and '7-Green' spinach (P < 0.05), with odds ratios of 2.2 and 3.3 for finding the pathogen on untreated versus treated greens, respectively. Salmonella was also 7.1 times more likely to be found on an untreated lettuce plant than on a lettuce plant sprayed with a 0.7% AA treatment solution (95% confidence interval [CI], 4.1 to 12.2; P < 0.0001). In studies addressing the efficacy of chitosan (0.1 or 0.3%), this chemical failed to reduce the prevalence of either pathogen on lettuce (P > 0.05). Similarly, spraying with 0.3% AA did not affect the prevalence of Salmonella on lettuce plants (P > 0.05); however, treatment solutions with 0.4% AA reduced the likelihood of detecting Salmonella in treated versus untreated plants by 6.6 times (95% CI, 2.1 to 20.9; P = 0.0007). After the lettuce was harvested and hand washed, consumers failed to distinguish either visually or organoleptically between untreated lettuce and lettuce sprayed with an acetic acid solution (P > 0.05). These results indicate that acetic acid could be used to reduce the microbiological risk of preharvest leafy greens.

Exploratory Study of the Application of Smoke Aerosols to Manure-Based Composting Materials To Reduce Prevalence of Salmonella.

During the early stages of aerobic composting, heat is generated and when the materials are self-insulating, extended exposure of pathogens to this heat source will lead to significant reduction, if not elimination, of the pathogens. However, when insufficient heat is applied to the composting materials, pathogens may survive. Under those conditions if the compost had contained material of animal origin or food waste, it would be considered untreated and would not be allowed in fields growing crops that may be consumed raw. However, alternative treatment processes are allowed, provided they are validated to meet the microbial standards stipulated in the Produce Safety final rule of the Food Safety Modernization Act and that the physical parameters of the process are documented to ensure that the conditions under which the process was validated have been met. Hence, this exploratory study was undertaken in a laboratory setting to determine the potential for application of aerosolized smoke to inactivate Salmonella in manure-based compost. Smoke generated from wood chips (oak or pecan) and introduced to the headspace of contaminated cow manure compost (≤3 log CFU/g) in sealed containers (35 g per container) resulted in no Salmonella detected by enrichment culture in 100% (0 of 14) of the samples after 18 to 48 h of exposure, whereas Salmonella in control samples remained at initial levels over the same time period. Shorter exposure times (6 h) to the smoke aerosols were less effective (11 of 24 samples positive by enrichment culture), and additional flushes with the wood smoke during this time failed to decrease the prevalence of contamination. Smoke aerosols generated from waste agricultural materials and held in containers with Salmonella-contaminated compost for 18 h significantly reduced the prevalence of the pathogen in samples compared with control samples (P < 0.05). The odds of not finding Salmonella in smoke-exposed compost were 14 (pine needles and rice hulls), 23 (cocoa hulls, orange rind, and peanut hulls), and 28 (sunflower hulls) times greater compared with samples not exposed to smoke. Many other variables remain to be examined (e.g., compost composition, compost maturity, and anaerobic conditions) to determine whether this approach could be universally applied to manure-based compost. Validation under field conditions will be required and may entail use of this approach in combination with suboptimal thermal conditions (<55°C).

Survival of Salmonella enterica and Escherichia coli O157:H7 Sprayed onto the Foliage of Field-Grown Cabbage Plants.

To reduce the number of cabbage pathogen outbreaks, it is essential to understand the fate of enteric pathogens that contaminate plants in the field. To assist in that effort, two independent trials were conducted with a red cultivar (cv. Red Dynasty) and a green cultivar (cv. Bravo F1) of field-grown cabbage ( Brassica oleracea var. capitata). In the first trial, plants with small heads were sprayed with an inoculum containing both attenuated Salmonella enterica Typhimurium and Escherichia coli O157:H7 (5.0 log CFU/mL). Initial pathogen levels (ca. 3.9 log CFU per head), determined through plate count enumeration (limit of detection was 1.3 log CFU/g), dropped precipitously such that 2 days later, they could not be detected by enrichment culture in 22 to 35% of the heads. However, subsequent declines were at a slower rate; no differences were observed between red and green cabbage heads ( P > 0.05), and heads were still positive for the pathogens 22 days after being sprayed with the inoculum. As a result, the logistic model revealed that for every 2 days contaminated cabbage heads remained in the field, the probability of finding a positive sample decreased by a factor of 1.1 (95% confidence interval from 1.0 to 1.2, P = 0.0022) and 1.2 (95% confidence interval from 1.0 to 1.4, P ≤ 0.0001) for Salmonella and E. coli O157:H7, respectively. In the second trial occurring 2 weeks later, plants with medium red or green cabbage heads were sprayed with an inoculum at a dose of 3.5 log CFU/mL. A similar decay in prevalence over time occurred for green cabbage as in trial 1; however, pathogen decline in red cabbage was less in trial 2 than in trial 1. The extended persistence of pathogens in cabbage heads exhibited in both trials infers that harvest of contaminated cabbage destined for raw consumption is risky. Additional field studies are necessary to determine whether similar pathogen fates occur in other regions or climates and to clarify the effect of the maturity of red cabbage on pathogen inactivation.

Survival and internalization of Salmonella and Escherichia coli O157:H7 sprayed onto different cabbage cultivars during cultivation in growth chambers.

BACKGROUND: Cabbage may become contaminated with enteric pathogens during cultivation. Using multiple cabbage cultivars at two maturity stages (small plants or plants with small heads) in growth chamber studies, the fate (internalization or surface survival) of Salmonella and Escherichia coli O157:H7 (0157) were examined in conjunction with any potential relationships to the plant's antimicrobial content. RESULTS: Internalized Salmonella was detected in cabbage within 24 h with prevalence ranging from 62% (16 of 26) for the 'Super Red 80' cultivar to 92% (24 of 26) for the 'Red Dynasty' cultivar. Surface survival of pathogens on small cabbage plants over nine days was significantly affected by cultivar with both pathogens surviving the most on the 'Farao' cultivar and Salmonella and O157 surviving the least on the 'Super Red 80' and 'Capture' cultivars, respectively (P < 0.05). Survival of O157 was slightly higher on cabbage heads for O157 than small plants suggesting that the maturity stage may affect this pathogen's fate. An inverse relationship existed between antimicrobial levels and the pathogen's surface survival on cabbage heads (P < 0.05). CONCLUSIONS: The fate of pathogens varied with the cabbage cultivar in growth chamber studies highlighting the potential to explore cultivar in field studies to reduce the risk of microbiological contamination in this crop. © 2019 Society of Chemical Industry.

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

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

Disposition of Salmonella and Escherichia coli O157:H7 following Spraying of Contaminated Water on Cucumber Fruit and Flowers in the Field.

Cucumbers are frequently consumed raw and have been implicated in several recent foodborne outbreaks. Because this item may become contaminated at the farm, it is vital to explore the fate of attenuated Salmonella Typhimurium or Escherichia coli O157:H7 sprayed onto foliage, flowers, and fruit in fields and determine whether pre- or postcontamination spray interventions could minimize contamination. After spraying cucumber plants with contaminated irrigation water (3.8 log CFU/mL of Salmonella Typhimurium and E. coli O157:H7), 60 to 78% of cucumber fruit were not contaminated because the plant's canopy likely prevented many of the underlying fruit from being exposed to the water. Subsequent exposure of contaminated cucumber plants to a simulated shower event did not appear to dislodge pathogens from contaminated foliage onto the fruit, nor did it appear to consistently wash either pathogen from the fruit. Spraying flowers and attached ovaries directly with a pathogen inoculum (4.6 log CFU/mL) initially led to 100% and 65 to 90% contamination, respectively. Within 3 days, 30 to 40% of the flowers were still contaminated; however, contamination of ovaries was minimal (≤10%), suggesting it was unlikely that internalization occurred through the flower to the ovary with these pathogen strains. In another study, both pathogens were found on a withered flower but not on the fruit to which the flower was attached, suggesting that this contaminated flower could serve as a source of cross-contamination in a storage bin if harvested with the fruit. Because pre- and postcontamination acetic acid-based spray treatments failed to reduce pathogen prevalence, the probability that fruit initially contaminated at 1.3 to 2.8 log CFU of Salmonella Typhimurium or E. coli O157:H7 per cucumber would be positive by enrichment culture decreased by a factor of 1.6 and 1.9 for Salmonella Typhimurium and E. coli O157:H7, respectively, for every day the fruit was held in the field ( P ≤ 0.0001). Hence, to reduce the prevalence of Salmonella Typhimurium on cucumbers below 5%, more than 1 week would be required.

Composting To Inactivate Foodborne Pathogens for Crop Soil Application: A Review.

Compost is organic material that has been degraded into a nutrient-stabilized humus-like substance through intense microbial activity, which can provide essential plant nutrients (nitrogen, phosphorus) to aid in the growth of fruits and vegetables. Compost can be generated from animal waste feedstocks; these can contain human pathogens, which can be inactivated through the heat and microbial competition promoted during the composting process. Outbreaks of infections caused by bacterial pathogens such as Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on fruit and vegetable commodities consumed raw emphasize the importance of minimizing the risk of pathogenic contamination on produce commodities. This review article investigates factors that affect the reduction and survival of bacterial foodborne pathogens during the composting process. Interactions with indigenous microorganisms, carbon:nitrogen ratios, and temperature changes influence pathogen survival, growth, and persistence in finished compost. Understanding the mechanisms of pathogen survival during the composting process and mechanisms that reduce pathogen populations can minimize the risk of pathogen contamination in the cultivation of fruits and vegetables.

Inactivation of Escherichia coli O157:H7 and Salmonella during washing of contaminated gloves in levulinic acid and sodium dodecyl sulfate solutions.

Field workers often wear gloves harvesting ready-to-eat produce; however, fields are not sterile environments and gloves may become contaminated numerous times during a working shift. This study explored the potential for inactivation of Escherichia coli O157:H7 and Salmonella when contaminated gloves were washed in levulinic acid (LV) and sodium dodecyl sulfate (SDS) solutions. Washing nitrile gloves with increasing concentrations of LV above 1.0% led to a decreased prevalence of glove contamination by Salmonella (P = 0.0000). A higher level of prevalence occurred for solid agar-cultured pathogens than liquid broth-cultured pathogens after nitrile gloves were washed in LV/SDS (P = 0.0000). Pathogens residing on latex gloves were more likely to be completely inactivated by washing in 0.5% LV/0.1% SDS solutions than nitrile or Canners gloves that exhibited inconsistent responses dependent on the pathogen strain. However, drying after washing nitrile gloves in 0.5% LV/0.1% SDS led to additional pathogen inactivation (P = 0.0394). Pathogen transfer from gloves to produce was implied as the pathogen prevalence on cantaloupe rind handled by LV/SDS-washed gloves was not statistically different from the prevalence on gloves (P = 0.7141). Hence, the risk of produce contamination may still exist but would be reduced by washing gloves in LV/SDS.

Inactivation of Escherichia coli O157:H7 and Salmonella deposited on gloves in a liquid state and subjected to drying conditions.

Gloves are worn by workers harvesting ready-to-eat produce as a deterrent for contaminating the produce with enteric pathogens that may reside on their hands. As fields are not sterile environments, the probability for gloves to become contaminated still exists and therefore it is critical to understand the conditions that affect the survival of pathogens on gloves. Both Escherichia coli O157:H7 and Salmonella deposited on glove surfaces in a liquid state survived longer when the pathogen had been suspended in lettuce sap than when suspended in water. Despite this protection, pathogens deposited on clean single-use gloves were more likely to survive during drying than pathogens deposited on dirty gloves (a film of lettuce sap had been applied to the surface prior to pathogen application and soil had been ground into the gloves). Survival of both E. coli O157:H7 and Salmonella was biphasic with the greatest losses occurring during the first hour of drying followed by much slower losses in the ensuing hours. Pathogens grown in rich media (tryptic soy broth) versus minimal media (M9) as well as those cultured on solid agar versus liquid broth were also more likely to be resistant to desiccation when deposited onto gloves. Although survival of E. coli O157:H7 on nitrile gloves was in general greater than it was on latex gloves, the relative survival of Salmonella on the two glove types was inconsistent. Due to these inconsistencies, no one glove type is considered better than another in reducing the risk for contamination with enteric pathogens. In addition, the extended survival of what are generally referred to as stress-resistant pathogens suggests that gloves either be changed frequently during the day or washed in a disinfectant to reduce the risk of glove contamination that could otherwise contaminate product handled with the contaminated gloves.

The Challenges of Eliminating or Substituting Antimicrobial Preservatives in Foods.

Consumers' criteria for evaluating food safety have evolved recently from considering the food's potential to cause immediate physical harm to considering the potential long-term effects that consumption of artificial ingredients, including antimicrobial preservatives, would have on health. As bacteriostatic and bactericidal agents to prevent microbial spoilage, antimicrobials not only extend shelf life, but they also enhance the product's safety. Antimicrobials and their levels that may be used in foods are specified by regulatory agencies. This review addresses the safety of antimicrobials and the potential consequences of removing those that are chemically synthesized or replacing them with antimicrobials from so-called natural sources. Such changes can affect the microbiological safety and spoilage of food as well as reduce shelf life, increase wastage, and increase the occurrence of foodborne illnesses.

Clostridium botulinum Toxin Production in Relation to Spoilage of Atlantic Salmon (Salmo salar) Packaged in Films of Varying Oxygen Permeabilities and with Different Atmospheres.

Shelf life of fish packaged under modified atmosphere (MA) is extended, but within the United States, commercial application of MA with impermeable packaging films is restricted due to concerns that botulinum toxin production would precede spoilage when contaminated fish are held at abusive storage temperatures. Use of semipermeable packaging films has been advocated; however, previous studies are inconclusive in determining the oxygen transmission rate (OTR) of a film that is needed to achieve an acceptable margin of safety (i.e., toxin production occurs only after spoilage). This study was conducted to determine the influence of OTR (target OTRs of 3 to 15,000) on the development of spoilage volatiles and toxin in salmon inoculated with type E Clostridium botulinum and subjected to air, vacuum, or 75:25 CO2:N2 MA and storage temperatures of 4, 8, 12, or 16°C. The most dominant headspace volatile peak that was produced during spoilage of samples at 4, 8 or 12°C was a peak, having a Kovats retention index (KI) of 753, and at which external standards of 2- or 3-methyl 1-butanol also eluted. Under anaerobic conditions, both the aerobic microbial populations and the size of the KI 753 spoilage peak were less in inoculated samples compared with uninoculated samples. C. botulinum-inoculated samples that were stored at 12 or 16°C under conditions favorable for anaerobic growth were also characterized by a KI 688 peak. Using a previously developed model that related the percentage of elderly consumers who would prepare a sample having the KI 753 spoilage peak of a specific size, it was determined that for salmon packaged with 3 or 3,000 OTR films under any atmosphere and stored at 12 or 16°C, 2 to 61% of the consumers could potentially prepare toxin-contaminated samples. Hence, when abusive storage conditions are suspected, the fish should not be consumed.

Development of Models To Relate Microbiological and Headspace Volatile Parameters in Stored Atlantic Salmon to Acceptance and Willingness To Prepare the Product by Senior Consumers.

Microbial spoilage of salmon occurs during extended refrigerated storage and is often accompanied by unpleasant aromas. When spoilage is detected, it is assumed that consumers will reject the product for consumption. Because sensory panels of trained individuals or consumers are expensive and labor intensive, identification of microbiological or chemical indicators to characterize the extent to which fish has spoiled is needed when experimental process and storage treatments are being evaluated. A consumer panel of 53 senior citizens (60 to 85 years of age) evaluated in duplicate raw salmon subjected to 10 storage conditions, and the fish quality was targeted to range from fresh to very spoiled. This population group was chosen because they would be expected to have a greater prevalence of olfactory impairments and higher odor thresholds than the general population; in turn, a shorter safety margin or time period between product rejection due to spoilage and the generation of Clostridium botulinum toxins would be likely. Low hedonic scores for aroma and overall acceptance (2 or 3 of 9), corresponding to "dislike very much" to "dislike moderately," did not equate with unwillingness to prepare the sample for consumption by up to seven panelists (13%) when the product was presumed to have already been purchased. Despite these outliers, significant models (P = 0.0000) were developed for the willingness of consumers to prepare the sample for consumption and the sample's aerobic and anaerobic microbiological populations and two volatile peaks with Kovats indices of 640 and 753. However, these models revealed that the levels of microbiological and chemical markers must be very high before some consumers would reject the sample; hence, spoilage detection by smell would likely not be an adequate safeguard against consuming salmon in which C. botulinum toxin had been generated.

Contamination of knives and graters by bacterial foodborne pathogens during slicing and grating of produce.

Poor hygiene and improper food preparation practices in consumers' homes have previously been demonstrated as contributing to foodborne diseases. To address potential cross-contamination by kitchen utensils in the home, a series of studies was conducted to determine the extent to which the use of a knife or grater on fresh produce would lead to the utensil's contamination with Escherichia coli O157:H7 or Salmonella enterica. When shredding inoculated carrots (ca. 5.3 log CFU/carrot), all graters became contaminated and the number of E. coli O157:H7 present on the utensil was significantly greater than Salmonella (p < 0.05). Contamination of knives after slicing inoculated produce (4.9-5.4 log CFU/produce item) could only be detected by enrichment culture. After slicing tomatoes, honeydew melons, strawberries, cucumbers, and cantaloupes, the average prevalence of knife contamination by the two pathogens was 43%, 17%, 15%, 7%, and 3%, respectively. No significant increase in the incidence or level of contamination occurred on the utensils when residues were present (p > 0.05); however, subsequent contamination of 7 produce items processed with the contaminated utensils did occur. These results highlight the necessity of proper sanitization of these utensils when used in preparation of raw produce.

Role of Brushes and Peelers in Removal of Escherichia coli O157:H7 and Salmonella from Produce in Domestic Kitchens.

Consumers are being advised to increase their consumption of fruits and vegetables to reduce their risk of chronic disease. However, to achieve that goal, consumers must be able to implement protocols in their kitchens to reduce their risk of consuming contaminated produce. To address this issue, a study was conducted to monitor the fate of Escherichia coli O157:H7 and Salmonella on produce (cantaloupe, honeydew melon, carrots, and celery) that were subjected to brushing or peeling using common kitchen utensils. Removal of similar levels of Salmonella from carrots was accomplished by peeling and by brushing, but significantly greater removal of E. coli O157:H7 from carrots was accomplished by peeling than by brushing under running water (P < 0.05). Brushing removed significantly fewer pathogens from contaminated cantaloupes than from other produce items (P < 0.05), suggesting that the netted rind provided sites where the pathogen cells could evade the brush bristles. A Sparta polyester brush was less effective than a scouring pad for removing Salmonella from carrots (P < 0.05). In all cases, brushing and peeling failed to eliminate the pathogens from the produce items, which may be the result of contamination of the utensil during use. High incidences of contamination (77 to 92%) were found among peelers used on carrots or celery, the Sparta brush used on carrots, and the scouring pad used on carrots and cantaloupe. Of the utensils investigated, the nylon brush had the lowest incidence of pathogen transference from contaminated produce (0 to 12%). Transfer of pathogens from a potentially contaminated Sparta brush or peeler to uncontaminated carrots did not occur or occurred only on the first of seven carrots processed with the utensil. Therefore, risk of cross-contamination from contaminated utensils to uncontaminated produce may be limited.

Effectiveness of levulinic acid and sodium dodecyl sulfate employed as a sanitizer during harvest or packing of cantaloupes contaminated with Salmonella Poona.

Freshly harvested Eastern variety cantaloupes (Cucumis melo L. var. reticulatus cv. Athena) were subjected to three different harvest and wash treatments to examine conditions under which the efficacy of the sanitizer, levulinic acid (LV) plus sodium dodecyl sulfate (SDS), could be enhanced to reduce Salmonella contamination. In treatment set one, cantaloupes were spot inoculated with Salmonella enterica serovar Poona (prepared from solid or liquid media cultures) before or after a 1-min dip treatment in LV (2.5, 5.0, 7.5, or 10%) and 2.5% SDS. S. Poona initial populations on rind tissue (4.26-5.04 log CFU/sample) were reduced to detection by enrichment culture when cantaloupes were subsequently exposed to any of the LV/SDS solutions. When S. Poona was introduced after cantaloupes had been dip-treated, greater decreases in pathogen populations at the stem scar were observed when cantaloupes were treated with increasing concentrations of LV. In treatment set two, the response of S. Poona dip-treated with 5% LV/2.5% SDS was compared to a simulated commercial dump tank treatment incorporating 200 ppm chlorine as well as a two-stage treatment employing both the chlorine tank and LV/SDS dip treatments. S. Poona levels (log CFU/sample or # positive by enrichment culture/# analyzed) after treatments were 5.25, 3.07, 7/10, 5/10 (stem scar) and 3.90, 25/40, 28/40, 20/40 (rind) for non-treated, chlorine tank, LV/SDS dip, and tank plus dip treatments, respectively. In treatment set three, freshly harvested cantaloupes were first treated in the field using a needle-free stem scar injection (200 µl, 7.5% LV/1.0% SDS, 60 psi) and a cantaloupe spray (30 ml, 7.5% LV/0.5% SDS). Cantaloupe stem scar and rind tissue were then spot-inoculated with S. Poona using either a liquid or soil-based medium followed by a simulated dump tank treatment incorporating either 200 ppm chlorine or 5% LV/2% SDS. S. Poona inoculated on field-treated cantaloupe rind decreased by 4.7 and 5.31 (liquid) and 3.27 and 3.36 (soil) log CFU/sample after simulated chlorine and LV/SDS tank treatments, respectively. In the case of stem scar tissue, S. Poona populations exhibited a 1.0 log greater reduction when cantaloupes were treated with LV/SDS compared to chlorine in the dump tank (P<0.05). Based on this study, application of multiple hurdles is warranted, as additional decreases in S. Poona populations were obtained when cantaloupes were subjected to a chlorine dump tank followed by a LV/SDS dip treatment.

The food industry's current and future role in preventing microbial foodborne illness within the United States.

During the past century, the microbiological safety of the US food supply has improved; however, many foodborne illnesses and outbreaks occur annually. Hence, opportunities for the food industry to improve the safety of both domestic and imported food exist through the adoption of risk-based preventive measures. Challenging food safety issues that are on the horizon include demographic changes to a population whose immune system is more susceptible to foodborne and opportunistic pathogens, climate changes that will shift where food is produced, and consumers' preferences for raw and minimally processed foods. Increased environmental and product testing and anonymous data sharing by the food industry with the public health community would aid in identifying system weaknesses and enabling more targeted corrective and preventive actions. Clinicians will continue to play a major role in reducing foodborne illnesses by diagnosing and reporting cases and in helping to educate the consumer about food safety practices.

Survival of Salmonella or Escherichia coli O157:H7 during holding of manure-based compost mixtures at sublethal temperatures as influenced by the carbon amendment.

During the early phases of aerobic composting of animal manures, pathogens are inactivated primarily from the accumulation of heat produced by indigenous microbial activity. When compost materials are not exposed to these lethal temperatures, the required holding time needed to obtain a pathogen-free product that may be applied to fields is unknown. Consequently, a series of studies examined whether the carbon amendment (wheat straw, peanut hulls, rice hulls, and pine needles) added to animal manures affected survival of either Salmonella or E. coli O157:H7 during storage of compost mixtures at sublethal temperatures (20 to 40°C). Pathogens consistently survived for longer periods of time in compost mixtures prepared with pine needles than compost mixtures prepared with either of the other three carbon amendments. Pathogen inactivation in wheat straw- or peanut hull-amended compost mixtures was dependent on the target pathogen, moisture level, and storage temperature. Moisture levels in wheat straw-amended compost mixtures stored at 40°C had no effect on inactivation of E. coli O157:H7. In contrast, wheat straw-amended mixtures stored at 30 to 35°C and equilibrated to suboptimal moisture contents (30 to 40%) were less effective for inactivating pathogens compared with drier (25% moisture) or moister (60% moisture) mixtures. In peanut hull-amended compost mixtures, inactivation of E. coli O157:H7 was affected minimally by moisture levels, whereas Salmonella survival increased as the moisture level was decreased. The different inactivation responses of Salmonella and E. coli O157:H7 in compost mixtures prepared with wheat straw or peanut hulls and equilibrated to different moisture levels suggest that there are different mechanisms for inactivation. Hence, developing reliable guidelines relying on time-temperature for holding of compost mixtures at sublethal temperatures will be challenging and, perhaps, not possible.

Manure source and age affect survival of zoonotic pathogens during aerobic composting at sublethal temperatures.

Heat is the primary mechanism by which aerobic composting inactivates zoonotic bacterial pathogens residing within animal manures, but at sublethal temperatures, the time necessary to hold the compost materials to ensure pathogen inactivation is uncertain. To determine the influence of the type of nitrogen amendment on inactivation of Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7 in compost mixtures stored at sublethal temperatures, specific variables investigated in these studies included the animal source of the manure, the initial carbon/nitrogen (C:N) ratio of the compost mixture, and the age of the manure. Salmonella and L. monocytogenes were both inactivated more rapidly in chicken and swine compost mixtures stored at 20°C when formulated to an initial C:N ratio of 20:1 compared with 40:1, whereas a C:N ratio did not have an effect on inactivation of these pathogens in cow compost mixtures. Pathogen inactivation was related to the elevated pH of the samples that likely arises from ammonia produced by the indigenous microflora in the compost mixtures. Indigenous microbial activity was reduced when compost mixtures were stored at 30°C and drier conditions (<10% moisture level) were prevalent. Furthermore, under these drier conditions, Salmonella persisted to a greater extent than L. monocytogenes, and the desiccation resistance of Salmonella appeared to convey cross-protection to ammonia. Salmonella persisted longer in compost mixtures prepared with aged chicken litter compared with fresh chicken litter, whereas E. coli O157:H7 survived to similar extents in compost mixtures prepared with either fresh or aged cow manure. The different responses observed when different sources of manure were used in compost mixtures reveal that guidelines with times required for pathogen inactivation in compost mixtures stored at sublethal temperatures should be dependent on the source of nitrogen, i.e., type of animal manure, present.

Inactivation of pathogens during aerobic composting of fresh and aged dairy manure and different carbon amendments.

Two separate studies were conducted to address the condition and the type of feedstocks used during composting of dairy manure. In each study, physical (temperature), chemical (ammonia, volatile acids, and pH), and biological (Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7) parameters were monitored during composting in bioreactors to assess the degree to which they were affected by the experimental variables and, ultimately, the ability of the chemical and physical parameters to predict the fate of pathogens during composting. Compost mixtures that contained either aged dairy manure or pine needles had reduced heat generation; therefore, pathogen reduction took longer than if fresh manure or carbon amendments of wheat straw or peanut hulls were used. Based on regression models derived from these results, ammonia concentration, in addition to heat, were the primary factors affecting the degree of pathogen inactivation in compost mixtures formulated to an initial carbon-nitrogen (C:N) ratio of 40:1, whereas, the pH of the compost mixture along with the amount of heat exposure were most influential in compost mixtures formulated to an initial C:N ratio of 30:1. Further studies are needed to validate these models so that additional criteria in addition to time and temperature can be used to evaluate the microbiological safety of composted manures.

Construction and characterization of outbreak Escherichia coli O157:H7 surrogate strains for use in field studies.

Escherichia coli O157:H7 has been the causative agent of many outbreaks associated with leafy green produce consumption. Elucidating the mechanism by which contamination occurs requires monitoring interactions between the pathogen and the plant under typical production conditions. Intentional introduction of virulent strains into fields is not an acceptable practice. As an alternative, attenuated strains of natural isolates have been used as surrogates of the virulent strains; however, the attachment properties and environmental stabilities of these attenuated isolates may differ from the unattenuated outbreak strains. In this study, the Shiga toxin (stx1, stx2, and/or stx2c) genes as well as the eae gene encoding intimin of two E. coli O157:H7 outbreak isolates, F4546 (1997 alfalfa sprout) and K4492 (2006 lettuce), were deleted. Individual gene deletions were confirmed by polymerase chain reaction (PCR) and DNA sequencing. The mutant strains did not produce Shiga toxin. The growth kinetics of these mutant strains under nutrient-rich and minimal conditions were identical to those of their wild-type strains. Attachment to the surface of lettuce leaves was comparable between wild-type/mutant pairs F4546/MD46 and K4492/MD47. Adherence to soil particles was also comparable between the virulent and surrogate pairs, although the F4546/MD46 pair exhibited statistically greater attachment than the K4492/MD47 pair (p≤0.05). Wild-type and mutant pairs F4546/MD46 and K4492/MD47 inoculated into wet or dry soils had statistically similar survival rates over the 7-day storage period at 20°C. A plasmid, pGFPuv, containing green fluorescent protein was transformed into each of the mutant strains, allowing for ease of identification and detection of surrogate strains on plant material or soil. These pGFPuv-containing surrogate strains will enable the investigation of pathogen interaction with plants and soil in the farm production environment where the virulent pathogen cannot be used.