Survival and growth of Salmonella Poona on and in tissues of cantaloupes co-infected with plant pathogenic molds and yeasts
Richards, Glenner Marie
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Multistate outbreaks of salmonellosis associated with consumption of fresh cantaloupes from salad bars suggest that contamination occurred early in the farm to fork chain, rather than immediately before consumption. Factors that may influence the adherence, survival, and growth of Salmonella enterica serotype Poona on and in cantaloupes were investigated. The effects of temperature differentials between cantaloupes and S. Poona suspensions at 4°C and 30°C, on changes in fruit weight and populations of the pathogen recovered from rinds and stem scar tissues of Eastern and Western type cantaloupes were assessed. The weight of immersed cantaloupes increased by 0.13 – 0.43%, with Western cantaloupes showing greater increases. Initial temperature of the inoculum and cantaloupe affected weight increase by Eastern cantaloupes, but not Western type cantaloupes. The histology of cantaloupe rind and stem scar tissues augments attachment and penetration by contaminating S. Poona, potentially reducing effectiveness of sanitizer treatments. Proteolytic activity and changes in pH of cantaloupe rind caused by growth of the phytopathogens Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Geotrichum candidum, and Penicillium expansum were studied. Survival and growth characteristics of S. Poona on the surface rind and in wounded tissue as affected by co-infection with molds and storage at 4°C and 20°C for up to 21 days were determined. Populations of S. Poona on intact and wounded rind tissues at 4°C decreased by 1 – 2 logs, but increased by 3 – 6 logs at 20°C. Co-infection with molds did not affect populations of S. Poona recovered from cantaloupe rinds. The pathogen migrated from wounded tissues in the rind through pulp tissues to distances as great as 3 – 4 cm below the surface, with or without coinfection with phytopathogens. Migration and survival of S. Poona in cantaloupes were enhanced by co-inoculation with C. cladosporioides and, to a lesser extent, P. expansum. Ten yeasts were screened for antagonistic activity against S. Poona in cantaloupe juice and decay by C. cladosporioides and G. candidum, in wounds on the surface of cantaloupe rind. Some of the yeasts demonstrated their potential to restrict colonization of wounded tissues by phytopathogenic molds, particularly at low storage temperatures. Test yeasts did not markedly restrict growth of S. Poona in cantaloupe juice.