P1-116 Salmonella Newport and Typhimurium Colonization of Fruit Differs from Leaves in Various Tomato Cultivars

Monday, August 4, 2014
Exhibit Hall D (Indiana Convention Center)
Sanghyun Han, University of Maryland, College Park, MD
Shirley Micallef, University of Maryland, College Park, MD
Introduction: Several outbreaks of Salmonella enterica infections have been linked to tomatoes. One cost-effective way to complement on-farm preventive measures such as Good Agricultural Practices (GAP) is to identify cultivars with inherent decreased susceptibility to Salmonella colonization. Although differential colonization of tomato leaves has been observed for different cultivars, fruit from various cultivars have not been assessed.

Purpose: The purpose of this study was to evaluate fruit and leaves of thirteen tomato cultivars (Solanum lycopersicum) with distinct phenotypes for their susceptibility to Salmonella epiphytic colonization.

Methods: Field-grown fruit or gnotobiotically-grown seedling leaves were spot inoculated with either a laboratory strain of S. Typhimurium or a tomato outbreak-associated strain of S. Newport.  Salmonella were retrieved and enumerated using direct plating after 24h for fruit and 72h for seedling leaves.  Differences in log CFU/unit of sample detected between levels of treatments were tested for significance using one-way ANOVA and Tukey’s HSD test.

Results: Epiphytic colonization of tomato fruit by S. enterica was cultivar-dependent and serotype-specific, but did not necessarily correlate with seedling leaf colonization. Fruit of cultivar ‘Heinz-1706’ were the least colonized by S. Newport, and ‘Mobox’ by S. Typhimurium, while the highest populations were retrieved from fruit of ‘Nyagous’, ‘LA4013’ and ‘Florida 91 VFF’ (P < 0.05). By contrast, seedling leaves supporting the lowest populations were ‘Florida 91 VFF’, ‘Movione’ and ‘Nyagous’ (P < 0.05). The tomato outbreak strain of S. Newport attained higher population densities on fruit than S. Typhimurium (P = 0.0002), suggesting better adaptation to tomato fruit colonization.

Significance: These data reveal that susceptibility of tomato fruit to Salmonella colonization is highly variable and could be one criterion for cultivar selection for cultivation.