The purpose of this project is to build on the premise of using “the right water for the right use,” augmenting current data on foodborne pathogen risk in surface water sources used for irrigation to ensure food safety and public health, while considering the crucial need to balance food safety with water resource preservation. Specifically, the goal of this project is to investigate the risk of Salmonella enterica occurrence at varying levels, persistence over time, and transmission to crops in surface waters of “undesirable” quality in a serovar-specific manner. The project will also augment food safety trainings for growers to enhance education on irrigation water safety.
Irrigation water quality is both an environmental and food safety issue, as water is a common source of contamination for foodborne pathogens. The Food safety Modernization act has compiled stringent guidelines for water quality to be used for growing fresh fruits and vegetables. This includes developing a water quality profile based on generic Escherichia coli levels for all irrigation sources used on produce covered by the regulation, as well as employing mitigation steps for water sources that are deemed below quality. Mitigation steps can include a wait period, employing drip tape irrigation, installing treatments in the drip line, or switching to groundwater for irrigation. While these interventions may address food safety concerns, all aforementioned actions require added cost, labor or time, and can detract from sustainable farming. For instance, UV water filters to improve microbial water quality are expensive to purchase, operate and maintain, and are energy-consuming. Chemical water treatments have environmental impacts and limited efficacy. Switching to other water sources such as groundwater places a burden on a precious natural resource and would constitute using “the wrong water for the wrong use .” Finally, the cost of maintenance and labor will stunt growth of small farms and discourage small farms from some markets.
While microbial safety of fresh produce is a priority, the obligation for growers to comply with current E. coli standards for water is imposed without knowledge of the “real” agricultural risk. One important foodborne pathogen, Salmonella enterica has historically been a food safety concern for agriculture on the eastern shore of Maryland , with multiple research teams identifying surface waters as a possible reservoir of this organism. However, Salmonella may or may not co-exist or correlate with E. coli levels, and the risk Salmonella poses if present in these waters is also not well understood[6, 7]. For Salmonella to successfully make the connection between persistence in environmental matrices and contamination on fresh produce, this organism must attach, mitigate stressors on the plant surface, and colonize. Elucidating environmental stressors relevant to Salmonella is paramount to developing targets for risk management in the field and differentiate between the observable risk of Salmonella in agricultural environments from the known hazard of its presence in water systems.
Many outstanding questions remain surrounding prevalence of Salmonella in surface water and the observed public health risk of irrigation with that water. Is there a threshold concentration below which Salmonella is unlikely to transfer onto crops or persist in soil? Does Salmonella in water become established in biofilms inside irrigation water distribution systems? Does Salmonella present in water make it more likely to establish on crops? Biofilms, whereby bacteria are strongly attached to surfaces, are a protective strategy for microbes against multiple common environmental stressors, and can facilitate successful colonization on plants[9-11]. It has been previously established that culturing media for bacteria can positively influence persistence on plants, such as pre-incubation of E. coli O157:H7 with manure extracts, but impact of environmental media on Salmonella has not been established. Finally, preferential plant colonization of some Salmonella serovars relative to others has been documented, but whether water environments impact this remains to be investigated . Data are needed to understand the agricultural risk of Salmonella presence in surface irrigation waters, to identify best practices that minimize contamination of crops rather than resorting to expensive and energy-consuming remedial actions or use of “higher quality” water such as groundwater that do not promote good environmental stewardship.
Food Safety trainings conducted by MDA in collaboration with the University of Maryland (UMD) provide a platform for interactive education on food safety issues and up-to-date research. How to implement on-farm interventions that minimize biological hazards during crop production, and how to develop a food safety plan are all covered during these trainings to functionally increase on-farm food safety practices. Water standards and testing are an important component of this training, but it is often difficult to convey and translate research findings to information growers can use, since so many data gaps on irrigation water-based microbial risks remain. The proposed research intends to fill these data gaps, enhancing understanding on water-based food safety risks and improve food safety trainings.
- Bell RL, Zheng J, Burrows E, Allard S, Wang CY, Keys CE, et al. Ecological prevalence, genetic diversity, and epidemiological aspects of Salmonella isolated from tomato agricultural regions of the Virginia Eastern Shore. Frontiers in Microbiology. 2015;6:415. doi: 10.3389/fmicb.2015.00415. PubMed PMID: PMC4423467.
- Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption, S. 21 CFR Parts 11, 16, and 112, Department of Health and Human Services(2015).
- Raudales RE. Characterization of water treatment technologies in irrigation: University of Florida; 2014.
- Perlman H. Groundwater depletion: U.S. Department of the Interior U.S. Geological Survey; 2016 [cited 2017 May 03]. Available from: https://water.usgs.gov/edu/gwdepletion.html.
- Bennett SD, Littrell KW, Hill TA, Mahovic M, Behravesh CB. Multistate foodborne disease outbreaks associated with raw tomatoes, United States, 1990–2010: a recurring public health problem. Epidemiology & Infection. 2015;143(07):1352-9.
- Benjamin L, Atwill ER, Jay-Russell M, Cooley M, Carychao D, Gorski L, et al. Occurrence of generic Escherichia coli, E. coli O157 and Salmonella spp. in water and sediment from leafy green produce farms and streams on the Central California coast. International Journal of Food Microbiology. 2013;165(1):65-76. doi: 10.1016/j.ijfoodmicro.2013.04.003. PubMed PMID: WOS:000320634900010.
- Winfield MD, Groisman EA. Role of nonhost environments in the lifestyles of Salmonella and Escherichia coli. Applied and Environmental Microbiology. 2003;69(7):3687-94. doi: 10.1128/aem.69.7.3687-3694.2003. PubMed PMID: WOS:000184082100001.
- Steenackers H, Hermans K, Vanderleyden J, De Keersmaecker SCJ. Salmonella biofilms: An overview on occurrence, structure, regulation and eradication. Food Research International. 2012;45(2):502-31. doi: 10.1016/j.foodres.2011.01.038. PubMed PMID: WOS:000302032200005.
- Yaron S, Römling U. Biofilm formation by enteric pathogens and its role in plant colonization and persistence. Microbial Biotechnology. 2014;7(6):496-516. doi: 10.1111/1751-7915.12186.
- Barak JD, Jahn CE, Gibson DL, Charkowski AO. The role of cellulose and O-antigen capsule in the colonization of plants by Salmonella enterica. Molecular Plant-Microbe Interactions. 2007;20(9):1083-91. doi: 10.1094/mpmi-20-9-1083. PubMed PMID: WOS:000253950800008.
- Barak JD, Gorski L, Naraghi-Arani P, Charkowski AO. Salmonella enterica virulence genes are required for bacterial attachment to plant tissue. Applied and Environmental Microbiology. 2005;71(10):5685-91. doi: 10.1128/aem.71.10.5685-5691.2005. PubMed PMID: WOS:000232504000003.
- Seo S, Matthews KR. Exposure of Escherichia coli O157:H7 to soil, manure, or water influences its survival on plants and initiation of plant defense response. Food Microbiology. 2014;38:87-92. doi: 10.1016/j.fm.2013.08.015. PubMed PMID: WOS:0003286604000
- Zheng J, Allard S, Reynolds S, Millner P, Arce G, Blodgett RJ, et al. Colonization and Internalization of Salmonella enterica in Tomato Plants. Applied and Environmental Microbiology. 2013;79(8):2494-502. doi: 10.1128/aem.03704-12. PubMed PMID: WOS:000316956200001.
The goal of this project is to evaluate the observed Salmonella risk to fresh produce safety in multiple surface water types. Specifically, I propose to assess Salmonella serovar viability in surface water over time, and investigate the degree of Salmonella transferability from surface water to fresh produce crops in growth chamber trials. Additionally, I plan to evaluate whether Salmonella adaptation to water environments increase the risk of water-crop transfer. Finally, in collaboration with the MDA I plan to enhance grower education by incorporating a seminar on irrigation water in Food Safety Trainings, sharing research findings and discussing the importance of balancing food safety practices with environmental stewardship. The goal of this project is to evaluate the observed Salmonella risk to fresh produce safety in multiple surface water types. Specifically, I propose to assess Salmonella serovar viability in surface water over time, and investigate the degree of Salmonella transferability from surface water to fresh produce crops in growth chamber trials. Additionally, I plan to evaluate whether Salmonella adaptation to water environments increase the risk of water-crop transfer. Finally, in collaboration with the MDA I plan to enhance grower education by incorporating a seminar on irrigation water in Food Safety Trainings, sharing research findings and discussing the importance of balancing food safety practices with environmental stewardship.
The objectives of this study are:
1) SURVIVAL: Measure the growth dynamics of multiple serovars of Salmonella in various types of surface irrigation water sources in Maryland. Fate of multiple Salmonella serovars in water samples representative of pond, non-tidal, and tidal river waters will determine whether viability in water is significantly influenced by water type or serovar. Salmonella will be quantified by both dilution plating and quantitative-PCR (q-PCR) using a standard curve that will enumerate not only culturable, but also non-culturable persistor phenotypes. Assessment of biofilm formation in these water microcosms will determine Salmonella serovar-dependent risk of biofilm formation in water distribution systems used in irrigation.
2) TRANSFERABILITY and ADAPTABILITY: Determine transferability potential of two Salmonella serovars from water to crops, and assess pre-adaptation to the plant-niche. I will assess the ability of Salmonella to establish on tomato via irrigation water contaminated with varying concentrations of this pathogen. This will investigate the relationship between Salmonella hazard in water and observed risk on plants. Biofilm formation, surface attachment, and stress response genes may be important for successful transfer of Salmonella onto plants. Gene expression analysis of these will evaluate Salmonella pre-adaptation to plant surface colonization.
3) FOOD SAFETY EDUCATION to MARYLAND GROWERS: Enhance food safety education for growers on water quality, testing requirements, and new research findings. Specifically, I will design a factsheet for online dissemination, and give seminars as part of Food Safety Trainings conducted by the MDA in collaboration with UMD. I will teach growers functional knowledge about water quality and testing, and employ scenario based case studies targeting best practices for addressing on-farm food safety risk factors. These seminars will also provide a platform to highlight the importance of implementing food safety measures while considering environmental sustainability and conservation.
To assess Salmonella population dynamics in various water types, filter-sterilized non-tidal river, tidal river, pond, and reclaimed water samples were inoculated with S. Heidelberg, Javiana, Typhimurium, Newport and serovar 4,5,12:i:- and enumerated over 30 days. A crystal violet attachment assay was conducted to investigate abiotic surface attachment. To assess transfer potential onto tomatoes, S. Javiana and Heidelberg were pre-incubated in water overnight before inoculation onto cv. ‘Red Robin’ tomato fruit for retrieval and quantification the next day.
S. enterica differentially persisted in water with respect to water type and serovar(p<0.05). Attachment strength varied significantly by water type; pond water supported the strongest attachment across serovars(p<0.05). S. Heidelberg exhibited the weakest attachment in all water types. Both S. Javiana and Heidelberg exhibited significantly higher transferability from all water types to tomatoes than from tryptic soy broth (p<0.05), but S. Javiana better colonized tomato fruit than S. Heidelberg (p<0.05).