Dataset Information

A System Model for Understanding the Role of Animal Feces as a Route of Contamination of Leafy Greens before Harvest.

ABSTRACT: The majority of foodborne outbreaks in the United States associated with the consumption of leafy greens contaminated with Escherichia coli O157:H7 have been reported during the period of July to November. A dynamic system model consisting of subsystems and inputs to the system (soil, irrigation, cattle, wild pig, and rainfall) simulating a hypothetical farm was developed. The model assumed two crops of lettuce in a year and simulated planting, irrigation, harvesting, ground preparation for the new crop, contamination of soil and plants, and survival of E. coli O157:H7. As predicted by the baseline model for crops harvested in different months from conventional fields, an estimated 13 out of 257 (5.05%) first crops harvested in July would have at least one plant with at least 1 CFU of E. coli O157:H7. Predictions indicate that no first crops would be contaminated with at least 1 CFU of E. coli O157:H7 for other months (April to June). The maximum E. coli O157:H7 concentration in a plant was higher in the second crop (27.10 CFU) than in the first crop (9.82 CFU). For the second crop, the probabilities of having at least one plant with at least 1 CFU of E. coli O157:H7 in a crop were predicted as 15/228 (6.6%), 5/333 (1.5%), 14/324 (4.3%), and 6/115 (5.2%) in August, September, October, and November, respectively. For organic fields, the probabilities of having at least one plant with ?1 CFU of E. coli O157:H7 in a crop (3.45%) were predicted to be higher than those for the conventional fields (2.15%).

Importance

This study is the first attempt toward developing a mathematical system model to understand the pathway of E. coli O157:H7 in the production of leafy greens. Results of the presented system model indicate that the seasonality of outbreaks of E. coli O157:H7-associated contamination of leafy greens was in good agreement with the prevalence of this pathogen in cattle and wild pig feces in a major leafy greens-producing region in California. On the basis of comparisons among the results of different scenarios, it can be recommended that the concentration of E. coli O157:H7 in leafy greens can be reduced considerably if contamination of soil with wild pig and cattle feces is mitigated.

SUBMITTER: Mishra A

PROVIDER: S-EPMC5203627 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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A System Model for Understanding the Role of Animal Feces as a Route of Contamination of Leafy Greens before Harvest.

Mishra Abhinav A Pang Hao H Buchanan Robert L RL Schaffner Donald W DW Pradhan Abani K AK

Applied and environmental microbiology 20161230 2

The majority of foodborne outbreaks in the United States associated with the consumption of leafy greens contaminated with Escherichia coli O157:H7 have been reported during the period of July to November. A dynamic system model consisting of subsystems and inputs to the system (soil, irrigation, cattle, wild pig, and rainfall) simulating a hypothetical farm was developed. The model assumed two crops of lettuce in a year and simulated planting, irrigation, harvesting, ground preparation for the ...[more]

PMID: 27836846

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Project description:Lettuce has been implicated in human norovirus (HuNoV) outbreaks. The virus is stable on the leaf surface for at least 2 weeks; however, the dynamics of virus internalization have not been fully investigated. The purpose of this study was to assess the internalization and distribution of HuNoV and two surrogate viruses, porcine sapovirus (SaV) and Tulane virus (TV), in lettuce and spinach. Viral inoculations through the roots of seedlings and the petiole of leaves from mature plants were performed, and the viruses were tracked on days 1 and 6 post-root inoculation and at 16 h and 72 h post-petiole inoculation. Confocal microscopy was used to visualize root-internalized HuNoV. In both lettuce and spinach, (i) HuNoV was internalized into the roots and leaves at similar RNA titers, whereas surrogate viruses were more restricted to the roots, (ii) all three viruses were stable inside the roots and leaves for at least 6 days, and (iii) HuNoV disseminated similarly inside the central veins and leaf lamina, whereas surrogate viruses were more restricted to the central veins. Infectious TV, but not SaV, was detectable in all tissues, suggesting that TV has greater stability than SaV. HuNoV was visualized inside the roots' vascular bundle and the leaf mesophyll of both plants. In conclusion, using surrogate viruses may underestimate the level of HuNoV internalization into edible leaves. The internalization of HuNoV through roots and cut leaves and the dissemination into various spinach and lettuce tissues raise concerns of internal contamination through irrigation and/or wash water.IMPORTANCE Human noroviruses are the leading cause of foodborne outbreaks, with lettuce being implicated in the majority of outbreaks. The virus causes acute gastroenteritis in all age groups, with more severe symptoms in children, the elderly, and immunocompromised patients, contributing to over 200,000 deaths worldwide annually. The majority of deaths due to HuNoV occur in the developing world, where limited sanitation exists along with poor wastewater treatment facilities, resulting in the contamination of water resources that are often used for irrigation. Our study confirms the ability of lettuce and spinach to internalize HuNoV from contaminated water through the roots into the edible leaves. Since these leafy greens are consumed with minimal processing that targets only surface pathogens, the internalized HuNoV presents an added risk to consumers. Thus, preventive measures should be in place to limit the contamination of irrigation water. In addition, better processing technologies are needed to inactivate internalized viral pathogens.

Project description:Giardia duodenalis is one of the most common food and water-borne intestinal parasites of humans and animals worldwide. Fresh, ready-to-eat produce such as leafy greens and salad mixes are considered potential transmission vehicles for Giardia infection in humans. Therefore, a specific, sensitive, and reliable method for Giardia detection in leafy greens is needed. We optimized washing procedures for the recovery of Giardia cysts from leafy greens and adapted and validated an existing EF1α LAMP assay for the detection of Giardia DNA to support routine diagnostic surveillance and disease outbreak investigations. Four leafy green types (35 ± 1 g) were spiked with 100 Giardia cysts and we compared washing by shaking with 1 M glycine (n = 20) or 0.1% Alconox (n = 20). DNA was extracted from washes, tested by LAMP and melt curve analysis, and time to positive (TTP) values compared. The detection limit was determined by spiking 10 (n = 40) Giardia cysts onto these same types of leafy greens and processing as above with 0.1% Alconox. Method robustness was assessed by subjecting spring mix (n = 45 total) to aging (1, 3 or 7 days) and washes to aging and freezing conditions prior to testing. Assay repeatability and specificity were evaluated, and an artificial positive control (APC) distinguishable by melt temperature (Tm) from DNA of Giardia spiked on leafy greens was designed to rule out cross-contamination from the control. Giardia detection rates were higher and TTP was lower (P < 0.05) for 0.1% Alconox (19/20, 8.85 ± 0.3 min) compared with 1 M glycine (15/20, 14.53 ± 7.2 min). The LAMP assay detected 10 Giardia cysts spiked on leafy greens in 13-34 min in 14/40 samples tested. Robustness assessment showed that TTP was higher (P < 0.0001) when spiked produce was stored for 7 days (13.09 ± 1.14 min) compared to fresh (9.72 ± 0.43 min). No unspiked samples were positive by LAMP, and the Tm for DNA of Giardia spiked on leafy greens was higher (P < 0.0001, 87.43 ± 0.05 °C) than the APC (86.43 ± 0.12 °C). Within-assay repeatability co-efficient of variation (CV) for TTP was 5.4% and no cross-contamination occurred when spiked and un-spiked samples were processed in alternate order. The optimized sample processing procedure combined with the EF1α LAMP assay is a sensitive, specific, labour-saving, and rapid method for the detection of Giardia cysts in leafy greens.

Dataset Information

A System Model for Understanding the Role of Animal Feces as a Route of Contamination of Leafy Greens before Harvest.

Importance

Publications

A System Model for Understanding the Role of Animal Feces as a Route of Contamination of Leafy Greens before Harvest.

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