The persistence of bacterial and viral contaminants on the surface of seeded produce, and their removal using mechanical and chemical treatments

Outbreaks of foodborne illness associated with consumption of fresh or minimally processed produce items are becoming an all too frequent occurrence. The attachment of these pathogens to the surface of produce items, their ability to persist under a variety of conditions, as well as their responses to disinfection treatments have not been adequately explored to date. Four produce items with distinctly different surface characteristics were selected for examination: strawberries, tomatoes, romaine lettuce, and cantaloupe. The pathogenic bacteria Escherichia coli O157:H7 and Salmonella Montevideo, both implicated in outbreaks associated with produce, along with the bacteriophages MS2, PRD1, Phi-X 174, and the enterovirus polio 1 were selected as challenge organisms. The ability of the bacteria and viruses to persist on tomatoes and strawberries as influenced by temperature, location, degree of processing (i.e., waxing), and organic load was examined. Efficacy of disinfection treatments, including chlorine and chlorine dioxide solutions, was evaluated. Challenge organisms were recovered up to 21 days post-inoculation from tomatoes, after 9 days on strawberries, and challenge organisms on both fruits were resistant to disinfection treatments evaluated. Romaine lettuce was inoculated with challenge organisms to identify localization preferences, examine their ability to persist under refrigerated storage, and evaluate efficacy of disinfection treatments. Inocula demonstrated a propensity toward attachment to leaf tip and midrib portions of pre-cut lettuce and persisted throughout the 14-day study. Statistically significant reductions were obtained by all the disinfection treatments examined, including chlorine solutions applied over a broad range of pH. Localization of challenge organisms on inoculated cantaloupe was examined, with preferential attachment observed for the stem scar. Disinfection treatments were examined and greater population reductions on cantaloupe surfaces were observed than for the other products examined. Bacteria and viruses were recovered up to 30 days post-inoculation from cantaloupe. The results of this study indicate bacteria and viral agents readily attach to produce surfaces and survived for extended periods under normal storage conditions. While significant reductions were obtained by the treatments evaluated, complete elimination of challenge organisms was not achieved. These findings stress the necessity to prevent produce contamination rather than relying on disinfection procedures.