Fate of foodborne bacterial pathogens in pesticide products

The 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 10(2) colony-forming units (cfu) ml(-1) into the following commercial pesticide products-Roundup, Boast & Merge, Gramoxone, Afolan, 2,4-D amine, Dithane M45, Benlate, Brave 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 degrees for 1h, survivor levels for all three E coli O157:H7 strains in pesticide solutions of Roundup, Roast & Merge, Gramoxone, Dithane M45, Ridomil 240EC and Lagon 480E were lower (P less than or equal to0.05) compared to their survival in water. In several pesticide solutions (Afolan, Brave 500, Lorsban 4E and Ambush 500EC), survivor levels were no different (P greater than or equal to0.05) from the control after Ih; however, by 24h, population levels of all strains in these four pesticide solutions were higher (P less than or equal to0.05) than those observed at Ih. 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 Brave 500, which consistently supported substantial growth of the other micro-organisms. Time course growth studies over 96h at 22 degreesC were conducted with Salmonella, Shigella, Listeria and E coli O157:H7 in solutions of Afolan, Brave 500, Lorsban 4E and Ambush 500EC. Overall, a 100 to 1060-fold increase in population was usually obtained in these pesticide solutions by 96h. Changes in either the initial inoculum level off coli O157:H7 from about 102 to 10(4)cfuml(-1) or temperature (from 20-22 to 31 degreesC) 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. (C) 2001 Society of Chemical Industry.