Investigating links between pathogen survival and contaminated irrigation water
Water is a potential source of microbial contamination for vegetable crops – whether applied through irrigation, crop protection sprays, or postharvest washes. Ongoing work is investigating how damage affects die off rates of pathogens applied through irrigation water. Project team member Dr Jenny Ekman from Applied Horticultural Research reports.
Many significant food safety outbreaks associated with salad greens can be traced back to contaminated water. Water that contains human pathogens such as E. coli, Salmonella spp. or Listeria monocytogenes can contaminate vegetables if it contacts the edible part.
Pathogen persistence from paddock to plate (VG16042) – a strategic levy investment under the Hort Innovation Vegetable Fund – found that E. coli and Salmonella on leafy vegetables fell below, or close to, detectable levels within 48 hours of irrigation. In contrast, bacteria could survive, and even multiply, if plants were physically damaged.
However, it was unknown whether natural damage from insect feeding or disease also increased persistence of human pathogens.
Investigations to answer these remaining questions are underway with funding from the Australian Centre for International Agricultural Research (ACIAR).
An initial trial in Cobbitty, New South Wales during spring 2020 evaluated die off rates of E. coli on lettuce. Lettuces were damaged through insect feeding (Heliothis), disease (Septoria leaf spot), or physical injury (leaf tips cut with scissors), then irrigated with water containing log 3.2 CFU/ml E. coli. Leaf samples were taken for microbial testing after 0, 1, 2, 3 and 6 days.Cutting leaves increased persistence
Average populations of E. coli multiplied ten-fold on physically damaged leaves within two days of damage and irrigation with contaminated water. In contrast, disease did not increase persistence relative to the undamaged controls, and Heliothis caterpillars had only a minor effect.
These results suggest that although avoiding physical damage is critical, insect feeding and disease do not affect the potential for contamination by irrigation water.
Perhaps, surprisingly, no previous studies have examined how food safety is affected by damage that can realistically occur during production. The trial will be repeated over spring and summer 2021 to confirm initial results.
ACIAR project (HORT 2016-188) is developing good agricultural practices for Filipino vegetable growers. In the Philippines, irrigation water is frequently contaminated, so the project is helping farmers reduce food safety risks. For more information, please contact Jenny Ekman or click here.
Guidelines on reducing risk from manure and safe use of irrigation water, as well as fact sheets produced by project VG16042, are available from the Fresh Produce Food Safety Centre website, Hort Innovation, Applied Horticultural Research and Freshcare.
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Please contact Dr Jenny Ekman at email@example.com. Applied Horticultural Research was supported by the Australian Centre for International Agricultural Research.