Evaluation of sampling protocol to provide science-based metrics for use in identification of Salmonella in irrigation water testing programs in mixed produce farms in the Suwannee River watershed.

Irrigation water has been linked to outbreaks of human foodborne illness and death associated with bacterial contamination of produce. In 2010, the FDAset forth a rule to allow for inspections of produce production systems, minimal standards to be derived for on-farm processes and resources such as quality of irrigation water. The rule also mandated documentation of actions conducted to minimize the risks of produce contamination. Requirements to document the quality of water are based on indicator bacteria and currently vary from no mandate for testing irrigation water quality to a presence/absence test to a single enumerated test to a 5-day geometric mean. There are no science-based metrics comparing the utility of these methods for detecting pathogenic bacteria in irrigation water sources. The proposed research will provide guidance for growers on water sampling methods to maximize the ability to detect bacterial contamination in surface water irrigation sources. In addition, the water sampling protocol developed in this study will provide a science-based method for collecting samples that can be documented as part of a water quality program to minimize risks of produce contamination.

Irrigation water is one of the foremost risks associated with food safety of fresh produce. Foodborne outbreaks of human disease and deaths have been linked to contamination of irrigation water with pathogenic bacteria (CDC, 2008; Greene et al., 2008). Currently, FDA is developing a rule that will establish science based minimum standards for the safe production and harvesting of fruits and vegetables and will address soil amendments, worker health and hygiene, packaging, temperature controls, water, and other issues (FDA, 2011). Although irrigation water is a recognized risk factor for bacterial pathogen contamination of produce, associated risks have not been systematically evaluated. Science-based data are needed to establish and validate Good Agricultural Practices (GAPs) metrics to prevent contamination of produce via irrigation water. In order to evaluate, modify, and implement GAPs, studies must establish appropriate assessment protocols for risk evaluation that are specific to each type of irrigation water system (surface, well, wastewater, etc.) used in a variety of produce production regions across the United States. Sampling protocols used in documenting quality of irrigation waters vary greatly in number of samples collected, timing and frequency of samples collected, sampling location, holding times prior to analysis, assay organism, and other factors. Bacteria populations are not uniformly distributed throughout surface water bodies, and concentrations fluctuate based on a variety of factors including temperature, solar radiation, and precipitation. Research-based comparisons of sampling protocol parameters are vital to growers to provide a method that most accurately measures pathogenic bacteria in irrigation water and provides information that is necessary to detect and mitigate contamination of irrigation water prior to transfer to crops. The proposed research will systematically evaluate methodologies associated with these parameters to identify and validate sampling procedures which increase the likelihood of detection of pathogenic and indicator bacteria contamination of surface irrigation waters. The safety of irrigation water used in production of fresh vegetables and fruit crops cannot be adequately assessed without a uniform system of sample collection and laboratory analysis based on sound science. Documented irrigation water quality plans will be an essential part of on-farm food safety programs. The following objectives will be addressed in this study: 1. Examine the effect of holding time following water sample collection on the survival rates of Salmonella and indicator bacteria. 2. Compare the utility of a composite sample collected from multiple locations in surface water to a single grab sample for maximizing probability of detection of Salmonella and indicator bacteria. 3. Compare concentrations and 5 day geometric means of Salmonella and indicator bacteria collected near vegetated buffer/pond and field/pond interfaces following precipitation events.

1. Compare the utility of a composite sample collected from multiple locations in surface water to a single grab sample for maximizing probability of detection of Salmonella and indicator bacteria. 

2. Explore the role of precipitation on Salmonella and indicator bacteria concentrations by a) Comparing 5-day geometric means of samples collected near vegetated buffer/pond interfaces to field/pond interfaces and b) Comparing 5-day geometric means to background levels established in Objective 1.

• A majority of the Salmonella isolates found in our water samples represented serotypes of Salmonella known to cause human illness. 

• A few of the isolates found in our water samples represented serotypes of Salmonella found in outbreaks of foodborne illness from fresh fruit/vegetable products. These include Salmonella serotypes Javiana and Newport. 

• Based on our main study, very low levels of Salmonella (of any serotype) were present in our water samples. Further research is needed to assess the actual likelihood of crop contamination from Salmonella present in irrigation water sources at varying levels.