Fate of foodborne bacterial pathogens in pesticide products

Abstract

AbstractThe effects of diluting concentrated pesticide products with water containing Escherichia coli O157:H7 (human, bovine and ground meat strains), Salmonella typhimurium, Salmonella enteritidis, Shigella sonnei, Shigella flexneri and Listeria monocytogenes were investigated. Individual cultures were inoculated at about 102 colony‐forming units (cfu) ml−1 into the following commercial pesticide products—Roundup, Poast & Merge, Gramoxone, Afolan, 2,4‐D amine, Dithane M45, Benlate, Bravo 500, Ridomil 240EC, Thiram 75WP, Sevin XLR+, Lorsban 4E, Diazinon 500, Ambush 500EC and Lagon 480E—following dilution with sterile tap water to recommended spray application concentrations (pesticide solution). Following incubation at 22 °C for 1 h, survivor levels for all three E coli O157:H7 strains in pesticide solutions of Roundup, Poast & Merge, Gramoxone, Dithane M45, Ridomil 240EC and Lagon 480E were lower (P ≤ 0.05) compared to their survival in water. In several pesticide solutions (Afolan, Bravo 500, Lorsban 4E and Ambush 500EC), survivor levels were no different (P≥0.05) from the control after 1 h; however, by 24 h, population levels of all strains in these four pesticide solutions were higher (P ≤ 0.05) than those observed at 1 h. Overall, similar survivor or growth patterns were observed with the remaining bacteria, with the exception of S flexneri. For this bacterium, survival or growth was poor, especially in Bravo 500, which consistently supported substantial growth of the other micro‐organisms. Time course growth studies over 96 h at 22 °C were conducted with Salmonella, Shigella, Listeria and E coli O157:H7 in solutions of Afolan, Bravo 500, Lorsban 4E and Ambush 500EC. Overall, a 100 to 1060‐fold increase in population was usually obtained in these pesticide solutions by 96 h. Changes in either the initial inoculum level of E coli O157:H7 from about 102 to 104 cfu ml−1 or temperature (from 20–22 to 31 °C) and concentration (from 0.5 to 1.5 times the recommended spray concentration) were shown to affect its growth in the pesticide solutions. The findings of this study indicate that some pesticide products, when diluted using contaminated water, may have the potential to promote growth of pathogens which could increase the risk of more widespread contamination of standing crops, including fruits.© 2001 Society of Chemical Industry