Particular cultivars of ripe tomatoes and dry, sunny conditions work together to increase the chances that salmonella will spread. (Credit: photon_de/Flickr)


‘Perfect storm’ spreads salmonella in tomatoes

Tomato variety and weather can combine to offer the perfect conditions for salmonella to proliferate in harvested tomatoes, a new study shows.

It remains unclear how much each contributes to salmonella’s spread, but scientists say understanding the process is key to eventually curbing produce-associated outbreaks.


The so-called perfect storm doesn’t happen often, says Massimiliano Marvasi, research assistant professor at the University of Florida, but can be damaging to public health and the food-crop business when it does.

During the past decade, fruits and vegetables have been among the foods most often linked to gastroenteritis outbreaks caused by E. coli and non-typhoidal salmonella. Those outbreaks resulted in public illness and multimillion-dollar losses for the food-crop industry.

Since 2006, at least 16 salmonella outbreaks have been linked to tomatoes, cantaloupes, sprouts, cucumbers, mangoes, peanut butter, and peppers, in addition to frozen foods containing plant products.

But scientists emphasize that less than 1 percent of supermarket produce contains salmonella or E. coli and the contamination becomes a problem only when it contaminates other food, or is consumed raw.

Sporadic outbreaks

Gastrointestinal illnesses caused by pathogens such as E. coli and salmonella pathogens have been sporadic—with scientists struggling to pinpoint exact causes—and their random nature argues for a perfect storm scenario.

“It is now clear that salmonella and other human pathogens can contaminate produce at any stage of the production cycle, from farm to fork,” the authors write.

The tomato industry follows strict protocols to prevent microbial food hazards in fresh fruits and vegetables, Marvasi says.

For the study, published in PLOS ONE, researchers wanted to find out which crop production factors are associated with tomato salmonella outbreaks. Specifically, they wanted to know how irrigation levels, waterlogged tomatoes and crop and pathogen genotypes affect salmonella’s ability to multiply in the fruit.

They grew three types of tomatoes—Bonny Best, Florida-47, and Solar Fire—during three production seasons over two years in Live Oak and Citra. Tomatoes had been harvested and injected with seven strains of salmonella.

Those three varieties were chosen because, in preliminary greenhouse experiments, they showed varying degrees of salmonella resistance, says Max Teplitski, associate professor of soil and water science. Bonny Best is an heirloom variety, often used as a control variety in plant pathogen experiments. Florida 47 and Solar Fire are newer varieties, widely grown commercially in the Southeast.

The findings show that particular cultivars combined with drier, sunnier conditions work together to increase the chances that salmonella will spread. Changing irrigation patterns caused little change in the potential for salmonella.

Tomato maturity and cultivar, particular strains of salmonella and seasonal differences were the strongest factors affecting proliferation. And ripe tomatoes were more vulnerable than green tomatoes.

Salmonella infection ranks among the most common foodborne illnesses, often spread by raw or undercooked meat, poultry, or eggs, but sometimes results from eating contaminated produce. Symptoms can include abdominal pain, fever, nausea, and vomiting.

In 2008, federal health officials erroneously blamed a salmonella outbreak on domestically grown tomatoes, but later said imported contaminated peppers were responsible. Growers in Florida and other states lost an estimated $100 million in sales.

Source: University of Florida

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