Persistence of Human Pathogens in Manure-Amended Australian Soils Used for Production of Leafy Vegetables

Jennifer Ekman, Adam Goldwater, Mark Bradbury, Jim Matthews and Gordon Rogers
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Jennifer Ekman: Applied Horticultural Research, Biosciences Building, 1 Central Avenue, Eveleigh, Sydney, NSW 2015, Australia
Adam Goldwater: Applied Horticultural Research, Biosciences Building, 1 Central Avenue, Eveleigh, Sydney, NSW 2015, Australia
Mark Bradbury: ARC Training Centre for Food Safety in the Fresh Produce Industry, School of Life and Environmental Sciences, University of Sydney, LEES Building, Chippendale, Sydney, NSW 2006, Australia
Jim Matthews: Sydney Informatics and Data Science Hub, University of Sydney, Queen St, Chippendale, Sydney, NSW 2006, Australia
Gordon Rogers: Applied Horticultural Research, Biosciences Building, 1 Central Avenue, Eveleigh, Sydney, NSW 2015, Australia

Agriculture, 2020, vol. 11, issue 1, 1-18

Abstract: Incorporation of manures into soil can add nutrients, improve soil structure and enhance biodiversity, thereby improving the sustainability of vegetable production systems. Unfortunately, manures can also potentially contain human enteric pathogens. To reduce the risk of contamination, Australian guidelines recommend a withholding period of 90 days between manure application and harvest for high-risk products such as leafy salad greens. Our study examined the appropriateness of these guidelines under conditions replicating those on a commercial vegetable farm. Cow manure and poultry litter with/without addition of non-pathogenic strains of Escherichia coli (E. coli) , Listeria innocua and Salmonella sv. sofia were added to sandy and clay loam soils typical of those used to grow vegetables. Bacterial populations were monitored in the soil and on crops of cos lettuce during spring (A), summer (B) and autumn (C) trials, with testing conducted by a commercial laboratory. Significant declines in E. coli occurred within 6 to 16 days in all trials. Modelling indicated that E. coli populations would be at or close to the limit of detection within 50 days for all of the combinations tested. A 2–3 log die-off of Salmonella spp. occurred within three weeks. However, occasional detections continued throughout trial A. As a result, the probability of detection after 50 days fell from 1.0 to 0.1 and 0.02 in trials B and C, respectively, but remained at 0.44 in trial A. Listeria spp. was the most persistent in soil but was not detected on lettuce at commercial maturity. While this study was limited in scope, the results suggest that a 90 day withholding period between application of manure and harvest significantly reduces risk from enteric pathogens under Australian field conditions.

Keywords: E. coli; Salmonella; Listeria; food safety; lettuce; leafy vegetable; manure (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2020
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