Several Salmonella enterica outbreaks have been traced back to contaminated tomatoes. In this study, the internalization of S. enterica Typhimurium via tomato leaves was investigated as affected by surfactants and bacterial rdar morphotype, which was reported to be important for the environmental persistence and attachment of Salmonella to plants. Surfactants, especially Silwet L-77, promoted ingress and survival of S. enterica Typhimurium in tomato leaves. In each of two experiments, 84 tomato plants were inoculated two to four times before fruiting with GFP-labeled S. enterica Typhimurium strain MAE110 (with rdar morphotype) or MAE119 (without rdar). For each inoculation, single leaflets were dipped in 109 CFU/ml Salmonella suspension with Silwet L-77. Inoculated and adjacent leaflets were tested for Salmonella survival for 3 weeks after each inoculation. The surface and pulp of ripe fruits produced on these plants were also examined for Salmonella. Populations of both Salmonella strains in inoculated leaflets decreased during 2 weeks after inoculation but remained unchanged (at about 104 CFU/g) in week 3. Populations of MAE110 were significantly higher (P<0.05) than those of MAE119 from day 3 after inoculation. In the first year, nine fruits collected from one of the 42 MAE119 inoculated plants were positive for S. enterica Typhimurium. In the second year, Salmonella was detected in adjacent non-inoculated leaves of eight tomato plants (five inoculated with strain MAE110). The pulp of 12 fruits from two plants inoculated with MAE110 was Salmonella positive (about 106 CFU/g). Internalization was confirmed by fluorescence and confocal laser microscopy. For the first time, convincing evidence is presented that S. enterica can move inside tomato plants grown in natural field soil and colonize fruits at high levels without inducing any symptoms, except for a slight reduction in plant growth.

Outbreaks of Salmonella enterica have been associated with water sources. Survival of S. enterica in various environments has been studied but survival in water has rarely been attempted. In two separate experiments, we examined the survival of S. enterica Typhimurium in clean spring water at various eutrophication levels and temperatures. In the first experiment, lasting for 135 days, survival of S. enterica (10(10) CFU/ml) in water with 0, 50, 100, 500, and 1,000 mg/liter of added carbon at 7, 17, and 27°C was monitored weekly. In the second experiment, lasting for 3 weeks, survival of S. enterica in water at 0, 100, and 200 mg/ liter of added carbon and 27°C was studied daily. Each experiment had four replicates. Dissolved organic carbon was measured daily in each experiment. At the beginning, midpoint, and end of the survival study, microbial communities in both experiments were assessed by denaturing gradient gel electrophoresis (DGGE). Even at minimal carbon concentrations, S. enterica survived for at least 63 d. Survival of Salmonella was highly dependent on eutrophication levels (as measured by dissolved organic carbon) and temperature, increasing at high eutrophication levels, but decreasing at high temperatures. Survival was also strongly affected by microbial competition or predation.

This 7-page fact sheet is one in a series of fact sheets discussing common foodborne pathogens of interest to food handlers, processors, and retailers. It covers the characteristics of, and symptoms caused by, the bacterium E. coli (particularly the “big six” strains), and also details how to minimize the risk of spreading or contracting an E. coli infection. Written by Bruna Bertoldi, Susanna Richardson, Renee Goodrich-Schneider, Ploy Kurdmongkoltham, and Keith R. Schneider and published by the UF/IFAS Department of Food Science and Human Nutrition, January 2018. http://edis.ifas.ufl.edu/fs233

A food is considered genetically modified when its genetic makeup is altered in some way as a result of the use of recombinant DNA biotechnological procedures. These changes result in the expression of attributes not found in the original. Examples include delayed-ripening tomatoes and pest-resistant or herbicide-tolerant crops. Genetic modification can be used to improve crop yields, reduce insecticide use, or increase the nutritional value of foods. This revised 5-page fact sheet answers questions consumers might have about genetically modified food. Written by Keith R. Schneider, Renée Goodrich Schneider, and Susanna Richardson, and published by the UF Department of Food Science and Human Nutrition, November 2014. (Photo: iStock/Thinkstock.com) FSHN02-2/FS084: Genetically Modified Food (ufl.edu)

The Food Safety Modernization Act that President Obama signed into law January 4, 2011 represents the most sweeping update to food safety regulation since the Federal Food, Drug, and Cosmetic Act of 1938. As part of FSMA, registration is required of facilities that manufacture, process, pack or hold food for human or animal consumption. This 3-page fact sheet was written by Susanna Richardson, Renée Goodrich Schneider, Mark A. Ritenour, Michelle D. Danyluk, and Keith R. Schneider, and published by the UF Department of Food Science and Human Nutrition, July 2013. http://edis.ifas.ufl.edu/fs231