Dispersal of Salmonella Typhimurium by Rain Splash onto Tomato Plants

Abstract

<jats:p>Outbreaks of Salmonella enterica have increasingly been associated with tomatoes and traced back to production areas, but the spread of Salmonella from a point source onto plants has not been described. Splash dispersal by rain could be one means of dissemination. Green fluorescent protein–labeled, kanamycin-resistant Salmonella enterica sv. Typhimurium dispensed on the surface of plastic mulch, organic mulch, or soil at 108 CFU/cm2 was used as the point source in the center of a rain simulator. Tomato plants in soil with and without plastic or organic mulch were placed around the point source, and rain intensities of 60 and 110 mm/h were applied for 5, 10, 20, and 30 min. Dispersal of Salmonella followed a negative exponential model with a half distance of 3 cm at 110 mm/h. Dispersed Salmonella survived for 3 days on tomato leaflets, with a total decline of 5 log and an initial decimal reduction time of 10 h. Recovery of dispersed Salmonella from plants at the maximum observed distance ranged from 3 CFU/g of leaflet after a rain episode of 110 mm/h for 10 min on soil to 117 CFU/g of leaflet on plastic mulch. Dispersal of Salmonella on plants with and without mulch was significantly enhanced by increasing rain duration from 0 to 10 min, but dispersal was reduced when rainfall duration increased from 10 to 30 min. Salmonella may be dispersed by rain to contaminate tomato plants in the field, especially during rain events of 10 min and when plastic mulch is used.</jats:p>

Farm Management, Environment, and Weather Factors Jointly Affect the Probability of Spinach Contamination by Generic Escherichia coli at the Preharvest Stage

“…Previous studies have also shown that storms and rain can increase produce contamination (34)(35)(36). These studies identified that rain splashed Salmonella Typhimurium onto tomato plants (34), splashed Colletotrichum acutatum onto strawberry fruits (36), and led to the transport of Salmonella Typhimurium to tomato fruits by aerosols (35). A modeling study showed that the probability of lettuce contamination with E. coli O157:H7 from manureamended soil was significantly correlated with the number of times it rained (37).…”

Metrics Proposed To Prevent the Harvest of Leafy Green Crops Exposed to Floodwater Contaminated with Escherichia coli

“…However, the recovery of the inoculated E. coli in soil from both surface and subsurface samples at the 9-m distance provides strong evidence for the subsurface lateral transport of E. coli contributing to the contamination of spinach foliar tissue at that distance. Rain splash of contaminated soil onto the spinach leaves during the heavy rainfall in the first few days after the initial flooding event may be the cause of the recovery of E. coli from the spinach leaves as rain splash has been shown to be a significant method of dispersal of bacteria in soil to plant tissue (16).…”

Scientific Opinion on the risk posed by pathogens in food of non-animal origin. Part 2 (Salmonellaand Norovirus in tomatoes)

“…Plastic mulch prevents direct contact of tomato fruits with foodborne pathogencontaminated soil (Guo et al, 2002a) but has the potential to enhance splash dispersal by rain or irrigation water. Cevallos-Cevallos et al (2012a) demonstrated that Salmonella may be dispersed by rain to contaminate tomato plants in the field, especially during rain showers of 10 minutes or more and when plastic mulch is used. They concluded that this was probably due, in part, to the different moisture levels on the tomato surface as both plastic and organic mulch stayed wet for at least 24 h after the rain, whereas soil dried within this time.…”