Salmonella can reach tomato fruits on plants exposed to aerosols formed by rain

Abstract: Outbreaks of Salmonella enterica have been associated with tomatoes and traced back to production areas but the spread of Salmonella in agricultural fields is still poorly understood. Post-rain Salmonella transfer from a point source to the air and then to tomato plants was evaluated. GFP-labeled kanamycin-resistant S. enterica serovar Typhimurium (108 CFU/mL) with and without expression of the rdar morphotype (rough colonies; cells with fimbriae and cellulose) was used as the point source in the center of a rain simulator. Rain intensities of 60 and 110mm/h were applied for 5, 10, 20, and 30min. Petri dishes with lactose broth and tomato plants with fruit (50–80cm high) were placed in the simulator after the rain had ceased. Salmonella recovery from air was maximum (300CFU/plate) after a rain episode of 60mm/h for 10min at distances of at least 85.5cm above the source and when the rdar morphotype strain was used. Small scale experiments showed that the smooth-colony strain without fimbriae precipitated from the air in significantly higher numbers than the rdar strain. Transfer of aerial Salmonella with the rdar morphotype to tomato fruits on plants followed a beta distribution (2.5950, 4.7393) within the generalized range from 0 to 30min of rain. Results show for the first time that Salmonella may transfer from rain to the air and contaminate tomato fruits at levels that could possibly be infectious to humans. [Copyright &y& Elsevier]