Longitudinal Assessment of the Dynamics of Escherichia coli, Total Coliforms, Enterococcus spp., and Aeromonas spp. in Alternative Irrigation Water Sources: a CONSERVE Study

Abstract

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.

Prevalence of Escherichia coli and Antibiotic-Resistant Bacteria During Fresh Produce Production (Romaine Lettuce) Using Municipal Wastewater Effluents

“…For all water types, higher E. coli counts ( p < 0.05) were observed in the vegetable crop growing (May-October) than non-growing (November-April) season. Additionally, this study found that bacterial counts in reclaimed water generally met microbial standards by federal guidelines or needed minimal mitigation ( Solaiman et al, 2020 ). Another recent work studied the prevalence of Shigatoxigenic E. coli (STEC) and atypical enteropathogenic E. coli (aEPEC) in untreated surface water and reclaimed water in the mid-Atlantic United States ( Haymaker et al, 2019 ).…”

“…A recent study conducted by Solaiman et al (2020) assessed the prevalence of bacteria indicating water quality, fecal contamination and crop contamination risk ( E. coli , total coliforms, Enterococcus , and Aeromonas ) over a 26-month longitudinal study in the mid-Atlantic region of the United States. For all water types, higher E. coli counts ( p < 0.05) were observed in the vegetable crop growing (May-October) than non-growing (November-April) season.…”

Microbial and physicochemical assessment of irrigation water treatment methods

“…Escherichia coli is a thermo-tolerant organism that is part of the coliform group that is considered as an indicator of faecal contamination (Steele and Odumeru, 2004). Studies done previously looking at the water quality in different regions of the United States have utilized E. coli and coliform populations as an indicator for assessing the microbiological safety (McEgan et al 2013;Havelaar et al 2017;Partyka et al 2018;Truitt et al 2018;Solaiman et al 2020). Some have shown a correlation between E. coli or coliform populations with target bacterial pathogens (Salmonella and Shiga-toxigenic E. coli) in surface water (Partyka et al 2016;Truitt et al 2018).…”

Zero-Valent Iron Filtration Reduces Microbial Contaminants in Irrigation Water and Transfer to Raw Agricultural Commodities

“…Non-traditional water sources in the Mid-Atlantic region of the United States were surveyed for Escherichia coli, total coliforms, and enterococci. These organisms were each detected in more than 85% of the 333 samples tested, and E. coli levels were significantly higher during the growing season of May through October, compared to other months [3]. Truitt et al evaluated Virginian surface waters used for agricultural irrigation during 2015 and 2016; Salmonella was detected in 19% of the four hundred samples collected [4].…”

“…In many studies where enteric pathogens and fecal contamination of water sources are investigated, the primarily focus on one type of organism [3][4][5][6][7]. However, bacteria and viruses are both found in human feces, but their structural differences create variations in the persistence and efficacy of water treatment technologies.…”