The effectiveness of treating irrigation water using ultraviolet radiation or sulphuric acid fertilizer for reducing generic Escherichia coli on fresh produce—a controlled intervention trial

• Published in: Journal of applied microbiology 2021-09, Vol.131 (3), p.1360-1377
• Main Authors: Beauvais, W., Englishbey, A.K., Marconi, C.M., Cholula, U., Belias, A.M., Wemette, M., Usaga, J., Churey, J.J., Worobo, R.W., Enciso, J., Anciso, J.R., Nightingale, K., Ivanek, R.
• Format: Article
• Language: English
• Subjects: Agricultural industry; Agricultural Irrigation; agriculture; Colony Count, Microbial; E coli; Environmental conditions; Escherichia coli; Escherichia coli - drug effects; Fertilizers; Food Contamination - prevention & control; Food Microbiology; food safety; Irrigation; Irrigation water; microbial contamination; Microorganisms; Original; Population dynamics; Production methods; Rifampin; Risk reduction; Soil contamination; Soil dynamics; Soil resistance; Soil surfaces; Soils; Spinach; Sulfuric acid; Sulfuric Acids; Surface irrigation; ultraviolet applications; Ultraviolet radiation; Ultraviolet Rays; Vegetables - microbiology; water; Water analysis; Water Microbiology; Water sampling
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1111/jam.15011

Aims The aims of this study were to: (i) estimate the effectiveness of ultraviolet radiation (UV) and sulphuric acid‐based fertilizer (SA), at reducing levels of generic Escherichia coli in surface irrigation water and on produce and surface soil in open produce fields; and (ii) describe the population dynamics of generic E. coli in produce fields. Methods and Results Spinach and cantaloupe plots were randomly assigned to control, UV or SA treatment groups. Irrigation water was inoculated with Rifampicin‐resistant E. coli prior to treatment. More than 75% of UV‐ and SA‐treated tank water samples had counts below the detection limit, compared to a mean count of 3·3 Log10 CFU per ml before treatment. Levels of Rifampicin‐resistant E. coli in soil and produce both increased and decreased over 10–15 days after irrigation, depending on the plot and time‐period. Conclusions UV and SA treatments effectively reduce the levels of E. coli in surface irrigation water. Their effectiveness at reducing contamination on produce was dependent on environmental conditions. Applying wait‐times after irrigation and prior to harvest is not a reliable means of mitigating against contaminated produce. Significance and Impact of the Study The results are of timely importance for the agricultural industry as new FSMA guidelines require producers to demonstrate a low microbial load in irrigation water or allow producers to apply a wait‐time to mitigate the risk of contaminated produce.