Persistence of Escherichia coli in the soil of an organic mixed crop‐livestock farm that integrates sheep grazing within vegetable fields

Abstract

Mixed crop-livestock farms (MCLF) integrate livestock and crops using their animals to graze crop residues and/or cover crops. MCLF are considered sustainable because grazing and the manure deposited by livestock enhance soil fertility and recycles farm nutrients. However, livestock manure may introduce enteric foodborne pathogens to the soil, which could contaminate fresh produce. Organic farmers in the United States follow the USDA National Organic Program (NOP) standards, which require 90 or 120 days between incorporating raw manure into the soil and harvest. Although not specifically addressed in NOP, organic farmers using grazing within production fields may also use this standard. The objectives of this study were to generate preharvest data to assess the die-off of generic Escherichia coli (E. coli) in the soil, after cover crops were grazed by sheep; and assess the genetic relatedness of generic E. coli isolates between soil and sheep faecal samples. We conducted a repeated observational study to evaluate the persistence of generic E. coli, as an indicator of faecal contamination and surrogate for STEC, in the soil of two fields (A and B) on an organic MCLF. Results showed a 3.70 log reduction in mean generic E. coli concentration MPN in the soil of field A from the highest of 3.70 log MPN/g on 48 day postsheep grazing (DPS) to -0.70 log MPN/g on 139 DPS. Field B showed a 3.51 log reduction in mean generic E. coli concentration in the soil from the highest mean of 3.51 log MPN/g on 14 DPS to the lowest mean -0.35 log MPN/g on 112 DPS. STEC prevalence in the sheep flock was 4.17% (1/24). Closely related generic E. coli strains were found between soil and faecal samples. Developing research-based waiting periods between grazing and harvest is important to inform best practices for farmers and food safety regulators.

Microbial Safety of Dairy Manure Fertilizer Application in Raspberry Production

“…This is consistent with previous finding that generic E. coli is a poor fecal indicator in soil from fresh produce field (Ceuppens et al, 2015). Generic E. coli can be present in non-fecal environment and has the ability to proliferate in the environment (Park et al, 2016; Patterson et al, 2018; Allard et al, 2019). The above evidence collectively reinforces the need to explore a suitable generic fecal indicator microorganism of soil.…”

Interaction between Fungal Communities, Soil Properties, and the Survival of Invading E. coli O157:H7 in Soils

“…Potential EcO157 source of SP and YJsoilsmay include the application of poorly composed organic fertilizer, feces of local livestock farms and wild animals, run-off from the piles of animal wastes, and pathogen-containing dust deposited into the land. Fresh vegetables and fruitsare important directions for the prevention and control of food-borne pollution [36].Microbial community structure and composition, as well as the soil physicochemical properties, might vary significantly in soils from different land-use types [37,38], and such variation might, in turn, influence the persistence ofpathogens invaded into those soils.However, the influence of soil abiotic and biotic factors on the survival of the invading human pathogensremains poorly understood.…”

Prevalence and risk factors associated withCampylobacterspp. andSalmonella entericain livestock raised on diversified small-scale farms in California

“…Livestock integration on these diversified farms (also called mixed crop-livestock farms or integrated livestock farms) may be classified temporally, spatially or based upon partial or full integration of animals and crops: spatially separated (livestock and crops are physically isolated), partial integration (animals and crops occupy the same field but at different times) and fully integrated (animals graze underneath or in between crops while they grow) [3]. DSSF that integrate livestock may use their animals to graze forage crops [3], post-harvest crop residues and/or cover crops [4]. Integrating livestock and cropland provides benefits, such as reducing pests or weeds, improving soil fertility, strengthening farm income and increasing regional food security [3].…”

“…Diversified farms are operations that raise a variety of crops (e.g. vegetables, orchard fruit, grapes) and/or multiple species of livestock, with the goal of utilising the products of one for the growth of the other, thereby fostering a sustainable cycle [2–4]. They are also often small-scale with the intent of selling directly to consumers [2, 3].…”