Salmonella splashing on produce

Nearly one-half of foodborne illnesses in the United States can be attributed to fresh produce consumption. The preharvest stage of production presents a critical opportunity to prevent produce contamination in the field from contaminating postharvest operations and exposing consumers to foodborne pathogens. One produce-contamination route that is not often explored is the transfer of pathogens in the soil to edible portions of crops via splash water.

We report here on the results from multiple field and microcosm experiments examining the potential for Salmonella contamination of produce crops via splash water, and the effect of soil moisture content on Salmonella survival in soil and concentration in splash water. In field and microcosm experiments, we detected Salmonella for up to 8 to 10 days after inoculation in soil and on produce. Salmonella and suspended solids were detected in splash water at heights of up to 80 cm from the soil surface. Soil-moisture conditions before the splash event influenced the detection of Salmonella on crops after the splash events—Salmonella concentrations on produce after rainfall were significantly higher in wet plots than in dry plots (geometric mean difference = 0.43 CFU/g; P = 0.03). Similarly, concentrations of Salmonella in splash water in wet plots trended higher than concentrations from dry plots (geometric mean difference = 0.67 CFU/100 mL; P = 0.04).

These results indicate that splash transfer of Salmonella from soil onto crops can occur and that antecedent soil-moisture content may mediate the efficiency of microbial transfer. Splash transfer of Salmonella may, therefore, pose a hazard to produce safety. The potential for the risk of splash should be further explored in agricultural regions in which Salmonella and other pathogens are present in soil. These results will help inform the assessment of produce safety risk and the development of management practices for the mitigation of produce contamination.

Salmonella survival in soil and transfer onto produce via splash events

December 2019

Journal of Food Protection vol. 82 no. 12


Rain day

In Canada we have snow days.

In Brisbane, we have rain days.

All schools are closed along the coast as cyclone Debbie drifts down to us. These are the first pics from the damage further north.

People in southern Ontario forget how to drive at the first hint of snow.

People in Brisbane forget how to drive when it rains.

Fortunately our house that is sliding down the hill is standing still — for now.

Don’t eat poop especially if it falls out of the sky onto birthday cake

I’ve been to some uncomfortable family gatherings where a few too many beer have led to awkward conversations. My experiences seem like a, uh, party next to what AOL reports happened to folks in Pennsylvania during a teenager’s sweet 16 party: the sky rained poop.

According to My Fox Philly, human waste rained down from the sky just after Jacinda blew out the candles on her cake, coating her guests and the rented canopy in feces. Her family believes the waste came from planes that were flying overhead and may have improperly disposed of the aircraft’s bathroom contents.

“Out of nowhere, from the sky, comes a bunch of feces, lands on her,” Jacinda’s dad told Fox.

The only thing more embarrassing than your party being ruined by poop rain is having your dad tell the local news about it afterwards.

Blame it on the rain

For the past decade fresh produce has consistently been at the top of the list of foods linked to outbreaks. Tomatoes, melons, leafy greens, fresh herbs and berries leading to illnesses all seem to make an appearance just about annually. Even though they aren’t really fresh produce, low moisture seeds and have also been in the game.

When it comes to production or minimally-processed linked outbreaks (like this, this and this) water is often fingered as a contamination factor. Either irrigation, wash or rain. barfblog friends and contributors Michelle Danyluk and Linda Harris co-authored some work pointing to wet orchards (from rain, a fairly uncommon event during almond harvest season) as a potential enabler for Salmonella migration through almond hulls and shells and into the kernel (the edible part).

In the most recent issue of Journal of Food Protection, rain enthusiast Michelle is at it again, coauthoring an investigation of the ability of rain to spread Salmonella Typhimurium from plastic mulch to a tomato plant.

Dispersal of Salmonella Typhimurium by rain splash onto tomato plants


Journal of Food Protection, Volume 75, Number 3, March 2012 , pp. 472-479(8)

Cevallos-Cevallos, Juan M.; Danyluk, Michelle D.; Gu, Ganyu; Vallad, Gary E.; van Bruggen, Ariena H.C.

Abstract: 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.

I don’t read this as "don’t eat tomatoes grown on plastic mulch that were rained on for 10 min" but info like this could be important to outbreak investigators trying to link an outbreak to a cadre of causative events.