Survival and Growth of attenuated Salmonella enterica serovars Newport and Typhimurium in Media Culture and Tomatoes
Fresh market tomatoes have been associated with 15 multistate Salmonella outbreaks between 1973 and 2010. While, S. enterica survival has been studied in tomato plants, field studies have been limited. To understand pathogen growth and survival, in crop fields, surrogate or attenuated organisms must be developed and validated. The purpose of this study was to compare the growth and survival of seven attenuated S. enterica Typhimurium and Newport strains against virulent strains S. Typhimurium ATCC14028 and S. Newport J1892 in optimum (TSB and TSB+kan) and minimal M9 growth media, and in commercial, red ripe tomatoes. Bacterial growth in media was assessed via BioScreen. Tomatoes were separately inoculated with 7 Log CFU/g of each isolate via vacuum infiltration, surface spot inoculation, or diced inoculation. Populations of each strain were determined on Days 0, 1, 3, and 5. In media, there were few differences in overall growth and growth rates between mutant isolates and wild-type (P<0.05). Growth in M9 was less (P<0.01), while growth rates were higher (P<0.01) than in TSB. In tomatoes (per treatment), there were no significant differences between growth rates of each isolate compared to WT (P>0.05); however, Salmonella strains in diced tomatoes had a higher growth rate than that in spot treated tomatoes (P>0.05). The growths of all the isolates in tomatoes indicated that under the tested conditions, isolates acted similarly to their WT counterparts. Thus, these strains may be able to be used as surrogate organisms in field studies.