WCFS - Western Center for Food Safety

Current Research

The Western Center for Food Safety (WCFS) is supported by a cooperative agreement to address the development of research approaches and data critical to high priority public health issues addressing FDA regulated fresh fruits, vegetables, and tree nuts. Such knowledge is critical to the development of scientifically validated “best practices” for mitigating those risks at the pre- and post-harvest production levels. The WCFS location near over 50% of the U.S. fresh fruit, vegetable and tree nut production, including the Salinas Valley, provides the FDA with the opportunity to conduct field trials in order to glean more information about current produce knowledge gaps in an area of the country that produces high volume of produce commodities. The knowledge gained from these studies on the West Coast has been used to enhance and expand collaborative research in other important produce production regions of the United States and Mexico.

Continuing Projects

Framework for developing research protocols to support proposed produce rule variances
Proposed Produce Preventive Controls Rule will contain standards for agricultural water that is directly applied to fresh produce and for raw manure that is used as a soil amendment. Alternate approaches to the proposed rule would likely be considered as adequate only if the operator can provide data from scientifically-valid studies to support that the proposed alternate controls as implemented are at least equally effective in reducing or eliminating pathogens. To address standardization of variance protocols, the WCFS hosted a meeting in late 2011 to begin the development of documents that provide a framework for designing field trials to evaluate survival of foodborne pathogens in the produce production environment. The first of the two documents (agricultural water) has been published and the second (soil amendments) will be submitted for publication in December 2012. The documents are available at the WCFS website.

Fate of Escherichia coli O157:H7 in field-inoculated lettuce and cilantro
The focus of this study was to understanding factors that impact the fate of E. coli O157:H7 and generic E. coli in field-and growth-chamber inoculated lettuce and cilantro plants. High humidity levels and conditions conducive to rapid desiccation consistently supported greater post-inoculation survival of E. coli O157:H7 in the laboratory. Inoculation of field lettuce or cilantro in the evening when humidity levels begin to increase also supported greater initial survival. Survival of Salmonella is better than for E. coli O157:H7 and both persist to a greater extent on cilantro. The data suggest that difference in the leafing green commodity may impact bacterial survival, which may lead to the development of different agricultural practices based on commodity.

Enhancing the safety of nuts and nut products
Nut and nut products have been implicated as the contamination vehicle in previous foodborne disease outbreaks. To complement ongoing field and laboratory studies on the safety of nuts and nut products, WCFS researchers conducted two separate risk assessments. In addition to these ongoing studies, the ability of Salmonella to survive in dry environments was also evaluated. The aims of the risk assessment were to: 1) assess the risk of salmonellosis associated with almond and pistachio consumption in North America, with current treatments in effect; 2) determine the resilience of the current production system to increases in prevalence or concentration of Salmonella on almonds and pistachios; 3) assess the impact of treating less than 100% of the crop; and 4) investigate conditions that could explain the number of cases associated with the 2001 almond outbreak. The ability of Salmonella to survive during desiccation was shown to be influenced by strain and environmental conditions. This work enhances food safety and hazard analysis efforts at FDA for nuts and nut products linked to outbreaks and recalls.

Enhancing the Quantitative Predictive Risk Assessment Model (QPRAM) for improved produce food safety
In a multi-year field trial (2011-2012) in the Salinas Valley, CA. WCFS researchers are generating real-world data regarding E. coli O157:H7 contamination of lettuce prior to harvest due to fecal pathogen transfer during foliar irrigation. Data from the first year study suggest that a 5-day interval between final irrigation and harvest combined with removal of the outer lower leaves from the head during harvest and due diligence to remove scat prior to final irrigation, would substantially reduce the risk of microbial contamination for lettuce. The initial data obtained by CFSAN assisted in the development of transfer coefficients – rates of pathogen transfer from soil to crops – to help inform the Produce Risk model, a quantitative risk assessment model under development by CFSAN.

Genomic characterization and animal infectivity of super-shedder compared to normative-shedder strains of E. coli O157:H7
In partnership with the National Cattleman’s Beef Association, this project is examining the role of super-shedder strains of E. coli O157:H7 to induce super-shedder infections in feedlot cattle.  Key questions for this project are what are the environmental, host, and bacterial factors that result in super-shedding cattle; these highly infected animals substantially elevated foodborne risk from contaminated beef products. Preliminary results suggest that oral ingested dose and not the phenotype of super shedding plays the dominant role in creating a long duration, high shedding infected animal. We are continuing to work with FDA and others on genomic characterization of the E. coli O157:H7 strains from this project to further clarify the role of the bacterial strain in this fecal shedding phenomenon. The findings will inform livestock producers about the potential risk of environmental dissemination of these pathogenic strains from the livestock production environment to nearby fresh produce fields and watersheds.

Microbial monitoring of irrigation water using high volume ultrafiltration for bacterial indictors and pathogens
This small project is in the queue to be conducted and is intended to build on the key findings from our CPS-funded project, Epidemiologic analysis and risk management practices for reducing E. coli in irrigation source water supplies and distribution systems. We have proposed that increasing the volume of water processed per assay from the standard of 100 ml to at least 1 liter will substantially increase the probability of correctly classifying irrigation water with respect to regulatory standards for microbial quality. Once we finalize our initial publication on this topic, our plan is to proceed with a field trial to verify the findings regarding the benefits of increasing sample volume for valid risk characterization. The data generated from this project will be shared with industry to enhance fresh produce irrigation water microbial testing schemes.

Sources and modes of transmission of foodborne pathogens in orchard environments
Over the past decade, contamination of California nuts with Salmonella has led to recalls and two outbreaks of salmonellosis in the U.S. The purpose of this study is to determine if contamination of almonds and pistachios with Salmonella is facilitated by movement of dusts into and around orchards and during initial post-harvest handling, and if airborne dust from adjacent animal feeding operations (cattle, poultry) may play a role in the spread of this pathogen. The air sampling methodology to measure movement of microorganisms from livestock/poultry operations to nearby almond and pistachio orchards was evaluated and optimized at two orchards during the 2012 harvest. Sampling and data analysis will continue in 2013 through the last harvest in October/November. Knowledge gained from this study will be shared with tree-nut and animal agriculture stakeholders to improve good agriculture practices that protect almond and pistachios from Salmonella contamination.

Developing scientifically-based food safety metrics for leafy greens and tomatoes
This project leverages a subaward to WCFS from the University of Maryland via the USDA NIFA Specialty Crop Research Initiative. WCFS and universities in five other states (Delaware, Florida, Maryland, New Jersey, Ohio) are conducting a three-year study aimed to develop scientifically-based food safety metrics for leafy greens and tomatoes. Two experimental field trials were conducted in 2012 in Salinas in parallel with the QPRAM trials. These Romaine lettuce trials were designed to evaluate the effectiveness of the LGMA 5-foot buffer zone around animal fecal material and the duration of survival of indicator E. coli in a fecal matrix. Preliminary analysis indicates that indicator bacteria may spread beyond 5-feet buffer immediately after irrigation, but the concentration drops several logs as the bacteria moves further from the fecal source. The indicator strain survived on outer Romaine leaves throughout the 11-day duration of the study, and differences in log reduction varied by type of feces (pig>rabbit>chicken). The research will provide scientific knowledge and data that will allow for the development of good agricultural metrics that can be used by the produce industry on a national basis for both domestic and imported produce.

Foodborne pathogen concentration and distribution in irrigation water systems at mixed produce farms in southeastern Georgia
The Suwannee rivershed is an important mixed produce production region comprising mostly small- to medium-sized farms in southeastern Georgia. Irrigation ponds are fed by dense dendritic stream networks and surrounded by extensive riparian buffer systems. This project leverages funds from the Center for Produce Safety and the Georgia Fruit and Vegetable Growers Association awarded to University of Georgia-Tifton (UGA) to study the ecology of foodborne pathogens in irrigation ponds in southeastern Georgia. WCFS established a subaward to assist with microbiological analysis of irrigation water samples. UGA collected and shipped water samples to the WCFS and CFSAN’s Office of Applied Research and Safety Assessment (OARSA) laboratories for detection and quantification of foodborne pathogens and indicator bacteria. Preliminary results indicate that Salmonella enterica is prevalent in these farm ponds, but the concentration is very low (<1 CFU/100 mls). The data from this study will be used to develop science-based approaches to improve GAP metrics in the southeastern U.S.

Identification of pre-harvest risk factors for foodborne pathogen transfer to fresh produce grown in desert environments
In 2008, an outbreak of E. coli O145 was traced to Romaine lettuce grown in Yuma, Arizona. Limited information exists on potential sources of shiga toxin-producing E. coli (STEC) and Salmonella that may contaminate agricultural water and fresh produce grown in the desert southwest. This leveraged project is a partnership between WCFS, local industry collaborators, and the Arizona Game and Fish Department. A survey of STEC and Salmonella prevalence in animals associated with intrusions into produce fields was conducted. WCFS staff also trained industry cooperators to use high volume ultrafiltration to test for bacterial indicators and pathogens in irrigation water. Preliminary findings indicate that STEC isolates are rarely isolated from domestic dog and wildlife samples, while Salmonella enterica was relatively common in all species tested. Future work will focus on assessing the relatedness and movement of STEC and Salmonella strains between domestic animals at livestock operations, terrestrial/avian wildlife, and irrigation canal water. Findings from this research will be used by industry partners in the desert production region to implement effective controls to protect fresh produce from microbial contamination.

New Projects

Survival of foodborne pathogen indicators following direct application of agricultural water to fresh basil in Hawaii
Since 2008, WCFS scientists have been leading field-based trials in experimental Romaine and cilantro plots in Salinas. These research studies aim to better understand the survival of field-borne microbial contaminants and leafy greens and herbs to inform the development and implementation of standardized, science- and risk-based approaches to good agricultural practices and outbreak investigations. Based on the success of these field trials, WCFS and the FDA Center for Food Safety and Nutrition (CFSAN) are engaging in a new collaboration with University of Hawaii at Manoa. The project aims to understand the survival of foodborne pathogens in tropical produce production environments. Linda Harris, Anne-Laure Moyne and Michele Jay-Russell visited Michael Melzer from the Department of Plant and Environmental Protection Sciences in November to discuss project design and identify potential experimental crops and locations for the early 2013 field trial. The collaboration expands the geographic scope of WCFS and will inform the industry on best food safety practices in tropical produce production regions.

Completed Projects

Evaluation of microbial communities in sediment basins and related conservation practices and their impact on nationwide food safety
Sediment basins on irrigated agricultural sites are an important conservation practice to capture and detain sediment laden runoff and allow sufficient time for the sediments to settle out. This project in collaboration with the USDA Natural Resources Conservation Service evaluated sediment basins of differing design and in differing ecological regions nationwide to determine which designs allow for maximal reduction of bacteria in surface water. While the use of sediment basins for the recovery of irrigation water has been proven to be effective in reducing sediment loads into waterways, the data obtained indicated that these surface waters may contain pathogenic bacteria, specifically Salmomella. This research demonstrates that re-using these waters for irrigation of ready-to-eat produce may pose a human health risk, which should be addressed in pre-harvest good agriculture practices. The findings will be used by industry and conservation stakeholders to improve good agriculture practices on farms that utilize sediment basins.

Epidemiologic analysis and risk management practices for reducing E. coli in irrigation source water supplies and distribution systems
WCFS conducted a comprehensive epidemiological analysis of irrigation water monitoring data currently being collected by the leafy greens produce industry in order to characterize the occurrence of generic E. coli, which has been used as an indicator of microbial produce contamination. Two datasets (2007-2010) were compiled that together represent a large number of produce growers from throughout California and from various sources of irrigation water across all seasons of the year. The data showed that the rate of exceedances was uncommon for most locations and sources of irrigation water used for leafy greens during this time period at the locations evaluated. This finding will provide useful information to FDA when developing guidance. In addition, this supports development of a risk-based approach to using generic E. coli to monitor irrigation water quality and suggests that testing could be reduced at locations with persistent high water quality and increased at locations that have a history of exceedances.

Strengthening good agricultural practices (GAPS) for reducing bacterial contamination of produce
WCFS conducted an extensive field sampling at enrolled produce farms and livestock operations in California’s central coast to identify potential sources and risk factors for microbial contamination of fresh leafy greens. Data from the multi-year (2008-2010) longitudinal study indicated that E. coli O157:H7 and Salmonella occur rarely on plants or soil during field production, but these pathogens are transiently prevalent in regional surface water, sediments, livestock, and wildlife populations. Generic E. coli concentration of pre-irrigation water was found to be positively associated with 24-hour cumulative rainfall and negatively associated with increasing distance between sample location and nearby vegetation or riparian habitat. Generic E. coli concentration in all water and sediment samples did not correlate with the presence of pathogens (E. coli O157, Salmonella). These findings are being used to refine GAP metrics for fresh produce related to irrigation water and environmental assessments.

Characterization and co-management of potential food safety risks from wildlife in riparian and wetland habitats near fresh produce fields
This CPS-leveraged research examined the impact of water quality factors and management practices on the occurrence of pathogens in cold-blooded vertebrates and waterbodies in and adjacent to fresh produce production areas in the central California coast and southeastern Georgia. Salmonella was cultured from common species of amphibians (frog, toad) and reptile (snake, lizard, turtle) samples in both states. All samples were negative for E. coli O157:H7 except a single tailwater pond sample in Monterey County, California. The findings provide the industry with data that is applicable to best practices in produce food safety addressing wildlife and water quality.

Cost-Benefit Analysis of Good Agricultural Practice(GAP) Metrics for Produce (2009-2010)
This study is a collaboration between the Western Center for Food Safety and  Drs. Helen H. Jensen and Sebastien Pouliot at Iowa State University. The goal of the project is to promote evidence-based decision making in pre-harvest food safety GAP metrics for fresh produce. The objective is to develop an assessment tool for a cost-benefit analysis of produce GAP interventions and associated metrics that integrates economics, epidemiology, and risk assessment.

Integration of risk assessment and economic modeling is becoming increasingly important to food safety risk managers in the US and Europe (as example:http://www.medvetnet.org/pdf/Reports/Report_06-003.pdf ). Recent foodborne illness outbreaks linked to fresh produce in the US have resulted in numerous pre-harvest commodity specific guidelines for produce food safety, and new or pending regulations at the state and national levels. These guidelines are based on the best scientific evidence available, to date, on risk factors and mitigation strategies to protect the food supply. Some of the management practices to prevent microbial contamination of produce in the field are very costly, and certain measures such as wildlife control may be in conflict with conservation and water quality goals for agriculture. This study proposes to use economic anlaysis to evaluate the costs and benefits of implementing GAP metrics for fresh produce.