Investigation of risk criteria and foodborne pathogen reduction practices for irrigation water

Irrigation water is considered to be one of the main contamination sources of foodborne pathogens on produce. Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes are three common enteric pathogens that may exist in irrigation water and are reported to be associated with produce contamination. Science-based data are needed to generate practical and accurate prediction methods and to establish effective strategies about decontamination of irrigation water to improve produce food safety. The purpose of this research project is to 1) Investigate practical criteria for the prediction of foodborne pathogens in irrigation pond and well water; 2) Evaluate the efficacy of commercial sanitizers on the decontamination of three common foodborne pathogens, Salmonella spp., E. coli O157:H7, and L. monocytogenes, in irrigation well and pond water; and 3) Provide education and training to stakeholders on improved agricultural practices to reduce the food safety risks in irrigation water. The outcomes of this research will benefit stakeholders especially vegetable and fruit industries to reduce the contamination risks of foodborne pathogens during irrigation and achieve the new requirements of FSMA on produce safety.

Current outbreaks of foodborne illnesses associated with vegetables and fruits attract more concerns about produce safety; irrigation water is considered to be one of the main contamination sources of foodborne pathogens on fresh produce. Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes are three common enteric pathogens that may exist in irrigation water and are reported to be associated with produce contamination. Science-based data are needed to generate practical and accurate prediction methods as well as effective decontamination strategies for irrigation water to mitigate contamination of produce by human pathogens at the production level. We propose to achieve research goals by fulfilling the following objectives: Investigate practical criteria for the prediction of foodborne pathogens in irrigation pond and well water. The spatial and temporal occurrence/population of foodborne pathogens, Salmonella spp., E. coli O157:H7, and L. monocytogenes, in irrigation pond and well water from four farms on the Eastern Shore of Virginia will be monitored and correlation to environmental parameters (temperature, rainfall, flood events, pH, dissolved oxygen, conductivity, and oxidation reduction potential), fecal indicator assessments (population of generic E. coli and fecal coliforms), diversity of bacterial communities, and presence or population of specific bacterial species will be assessed. Evaluate the efficacy of commercial sanitizers on the decontamination of three common foodborne pathogens, Salmonella spp., E. coli O157:H7, and L. monocytogenes, in irrigation well and pond water. The effects of four sanitizers, Clorox® Regular-Bleach, CDG Solution 3000™, Sanidate 5.0, and Sanidate 12.0 will be tested. Population reduction of foodborne pathogens will be compared after sanitizer treatments. Impacts of bacterial initial concentration levels (population densities of 8 log, 6 log, or 4 log CFU/ml), irrigation water sources (well or pond waters from four farms), water parameters (temperature, pH, dissolved oxygen, conductivity, and oxidation reduction potential), and bacterial communities including population of generic E. coli and fecal coliforms, on the reduction and available active ingredients of tested sanitizers will be also analyzed. Provide education and training to stakeholders on improved agricultural practices to reduce the food safety risks in irrigation water. Practices to mitigate food safety risks in irrigation water will be shared with stakeholders. This study will evaluate the efficacy of physicochemical indicators and biological index organisms on the prediction of foodborne pathogen contamination in irrigation pond and well water. Analysis of the relationship between bacterial species and foodborne pathogens will improve current prediction and prevention strategies. Economical and efficient decontamination methods for irrigation water treatment will also be investigated based on the results of proposed study and shared with vegetable and fruit producers and other stakeholders. The outcomes of this research will benefit stakeholders especially vegetable and fruit industries to reduce the contamination risks of foodborne pathogens during the production and achieve the new requirements of FSMA on produce safety.

1) Investigate practical criteria for the prediction of foodborne pathogens in irrigation pond and well water. 

2) Evaluate the efficacy of commercial sanitizers on the decontamination of three common foodborne pathogens, Salmonella spp., E. coli O157:H7, and Listeria monocytogenes, in irrigation well and pond water. 

3) Provide education and training to stakeholders on improved agricultural practices to reduce the food safety risks in irrigation water.

This study found that Salmonella populations of selected samples per month and the average MPN values for each month were not correlated (p > 0.1). Weekly differences of Salmonella occurrence and populations in water samples among the same detection month indicated that intensive sampling would be necessary to identify the accurate spatial and temporal pattern of the foodborne pathogen in irrigation water. In addition, the low probability and concentration of Salmonella in collected water samples indicate that large sample amount or additional replicates (>3) would be important to find out the real prevalence in environmental samples. Distribution and diversity of Salmonella serovars varies among different types of water samples and in two sampling years, i.e., the dominant Salmonella serovar in water samples collected in 2014 was Newport (data for 2015 will be provided at the CPS 2016 Symposium). Further genotypic analyses using whole genomic sequencing of selected Salmonella strains isolated from this study will be conducted and the data will be compared with identified or sequenced clinical and environmental strains from previous studies. In addition, survival comparison study and genetic analysis will be performed to compare different strains isolated from this agricultural area, like strains of serovars Newport and Typhimurium, to identify specific bacterial properties and/or mechanisms that contribute to colonization and survival variances of Salmonella in different environments. The low correlation coefficient between fecal indicators, including generic E. coli, and foodborne pathogens in irrigation water suggests further efforts to identify more suitable indicator microorganisms or other biological markers. In addition, the prevalence and population difference of different foodborne pathogens (Salmonella spp. and L. monocytogenes in this study) in the same water samples as well as the high variance among different farms (location) bring challenges to just using one universal indicator or standard to evaluate contamination risks in agricultural water. Microbial community analysis through metagenomics provides clues to identify suitable alternative indicators and/or potential suppressors of foodborne pathogens in agricultural water for produce production. Additional searches for Listeria and Salmonella enterica were performed using the high-resolution Resphera Insight protocol; however, additional sample data are required to provide sufficient frequency in the dataset to provide a complete confident positive call. Due to budget and time limitations, only monthly water samples tested for both foodborne pathogens were selected for metagenomic analysis. Further 16s amplicon sequencing of all weekly samples (392) and subsequent computational analysis are needed to achieve a final definite conclusion. In addition, metagenomic analyses to identify eukaryotes and metabolites in irrigation water samples are underway to investigate their relationship with foodborne pathogens and to evaluate their potentials as suitable predictors. Further data analysis will be performed by principal component analysis, partial least square, stepwise and canonical discriminant analyses to identify variables and OTUs or a certain group (pattern) of variables that contributed most to the classification (pathogen presence/absence or different levels of Salmonella and Listeria monocytogenes population). Additional results will be reported at the CPS 2016 Symposium. Results derived from this study provide information for local farmers and other stakeholders to recognize the contamination risks of agricultural production with irrigation in the major horticultural area of Virginia. The prevalence, population and diversity of Salmonella strains in major produce production regions, like VA, CA, FL, GA, NY etc., need to be compared to analyze the variance of foodborne pathogens for future outbreak prediction and mitigation. Irrigation water was hypothesized to be one of the main contamination sources of Salmonella within production fields. Suitable decontamination methods for large irrigation water systems to control foodborne pathogens became an urgent request from vegetable and fruit farmers. The instant efficacy of hydrogen peroxide and PAA (Sanidate 5.0 and 12.0) at low application levels on the disinfection of foodborne pathogens in irrigation water is relatively lower compared with sodium hypochlorite (XY-12) and chlorine dioxide (CDG300). For 1-min contact time, the population of tested foodborne pathogens treated with hydrogen peroxide and PAA was significantly higher than water samples treated with sodium hypochlorite and chlorine dioxide. However, the residual concentration of active ingredient of PAA was significantly higher than that of sodium hypochlorite and chlorine dioxide after 30-min contact time, which could prevent subsequent contaminations. Further studies can be performed by inoculating additional foodborne pathogens into treated water samples after 30-min contact time to evaluate the prevention efficacy. So for instantaneous treatment, use of sodium hypochlorite and chlorine dioxide products would be recommended. However, constant detection of active ingredients and retreatment with these products would be necessary to maintain pathogen-free agricultural waters. In conclusion, considering the low population densities of foodborne pathogens in the irrigation water of this ESV region as detected in objective 1 (less than 2 log MPN/L), all test sanitizers would be qualified for irrigation water decontamination. Further studies would be necessary to investigate the effects of various disinfectants and the application in large irrigation systems in vegetable and fruit farms for food safety management.