Irrigation water contaminated with Salmonella enterica and Listeria monocytogenes may provide a route of contamination of raw or minimally processed fruits and vegetables. While previous work has surveyed specific and singular types of agricultural irrigation water for bacterial pathogens, few studies have simultaneously surveyed different water sources repeatedly over an extended period of time. This study quantified S. enterica and L. monocytogenes levels (MPN/L) at 6 sites, including river waters: tidal freshwater river (MA04, n = 34), non-tidal freshwater river, (MA05, n = 32), one reclaimed water holding pond (MA06, n = 25), two pond water sites (MA10, n = 35; MA11, n = 34), and one produce wash water site (MA12, n = 10) from September 2016-October 2018. Overall, 50% (84/168) and 31% (53/ 170) of sampling events recovered S. enterica and L. monocytogenes, respectively. Results showed that river waters supported significantly (p < 0.05) greater levels of S. enterica than pond or reclaimed waters. The non-tidal river water sites (MA05) with the lowest water temperature supported significantly greater level of L. monocytogenes compared to all other sites; L. monocytogenes levels were also lower in winter and spring compared to summer seasons. Filtering 10 L of water through a modified Moore swab (MMS) was 43.5 (Odds ratio, p < 0.001) and 25.5 (p < 0.001) times more likely to recover S. enterica than filtering 1 L and 0.1 L, respectively; filtering 10 L was 4.8 (p < 0.05) and 3.9 (p < 0.05) times more likely to recover L. monocytogenes than 1L and 0.1 L, respectively. Work presented here shows that S. enterica and L. monocytogenes levels are higher in river waters compared to pond or

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As climate change continues to stress freshwater resources, we have a pressing need to identify alternative (non-traditional) sources of microbially safe water for irrigation of fresh produce. This study is part of the center CONSERVE, which aims to facilitate the adoption of adequate agricultural water sources. A 26-month longitudinal study was conducted at 11 sites to assess the prevalence of bacteria indicating water quality, fecal contamination and crop contamination risk (Escherichia coli, total coliforms (TC), Enterococcus, Aeromonas). Sites included non-tidal freshwater rivers/creeks (NF), a tidal brackish river (TB), irrigation ponds (PW) and reclaimed water sites (RW). Water samples were filtered for bacterial quantification. E. coli, TC and enterococci (∼86%, 98% and 90% positive, respectively; n=333), and Aeromonas (∼98% positive; n=133) were widespread in water samples tested. Highest E. coli counts were in rivers, TC counts in TB rivers and enterococci in rivers and ponds (all p<0.001), compared to other water types. Aeromonas counts were consistent across sites. Seasonal dynamics were detected in NF and PW samples only. E. coli counts were higher in the vegetable crop-growing (May-October) than non-growing (November-April) season in all water types (p<0.05). Only one RW and both PW sites met the US Food Safety Modernization Act water standards. However, implementation of recommended mitigation measures of allowing time for microbial die-off between irrigation and harvest would bring all other sites into compliance within two days. This study provides comprehensive microbial data on alternative irrigation water and serves as an important resource for food safety planning and policy-setting. Importance Increasing demands for fresh fruit and vegetables, a variable climate impacting agricultural water availability and microbial food safety goals are pressing the need to identify new, safe, alternative sources of irrigation water. Our study generated microbial data collected over a two-year period from potential sources of irrigation (rivers, ponds and reclaimed water sites). Pond water was found to comply with Food Safety Modernization Act (FSMA) microbial standards for irrigation of fruit and vegetables. Bacterial counts in reclaimed water, a resource that is not universally allowed on fresh produce in the US, generally met microbial standards or needed minimal mitigation. We detected the most seasonality and the highest microbial loads in river water, which emerged as the water type that would require the most mitigation to be compliant with established FSMA standards. This dataset represents one of the most comprehensive, longitudinal analysis of alternative irrigation water sources in the United States.

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Plant growth-promoting rhizobacterium Bacillus subtilis UD1022 has been shown to trigger an induced systemic response in Arabidopsis thaliana. This interaction causes plant stomata to close, protecting the plant from infection by plant pathogens and thereby increasing crop yield. The purpose of this study was to determine whether UD1022 applied to the roots of plants is able to induce stomata closure in leafy greens as well as influence the persistence of human pathogens (Listeria and Salmonella) on plants. UD1022 induced stomata closure in the presence of human pathogens on both lettuce and spinach 3 h post-inoculation (p<0.0001). Results were confirmed by root inoculation with heat-killed UD1022, which did not induce stomata closure. Presence of UD1022 on lettuce roots significantly reduced the persistence of Listeria on plants after 3 days post-inoculation (p=0.02) but had less of an effect on the persistence of Salmonella. The results of this study indicate that plant growth-promoting rhizobacterium B. subtilis UD1022 may be able to prevent contamination by some human pathogens. This is the first study to investigate the use of plant growth-promoting rhizobacteria to control the persistence of human pathogens on plants.