Pre-bagged salads are what they are—you toss a couple in your cart when you're short on time or feeling guilty about the Krispy Kremes you crushed at three in the morning.
A new study in the journal Applied and Environmental Microbiology, however, may convince you to dice your own spinach from here on out; "salad juices"—uh, gross—from damaged leaves are up to 2,400 times more likely to lead to salmonella contamination. Or as the study authors put it: "significantly enhanced Salmonella enterica salad leaf colonisation."
In the study, researchers used a mortar and pestle to grind up the salads and then analyzed the resulting juices for the presence of the icky bacteria that can lead to diarrhea, fever and abdominal cramps.
When salad juices released during the chopping process drip out of the leaves, they can get caught in the bag and become a hotbed for salmonella growth, researchers found. More alarmingly, the salmonella spread even when the damaged leaves were refrigerated.
You may be thinking, "I always wash my salad after I take it out of the bag." Well, the researchers also found that trace amounts of the salad juice can stick to leaves even after they're washed, which primes you for infection.
Salad leaves are prime real estate for the microbial pathogens that cause salmonella due to a complicated and risky harvesting process: It takes all kinds of implements—and people—that you don't see to cut the leaves from stalks, trim them, and then wash and package them for transport, the researchers say. All those variables don't bode well for the plant tissues, which allow salmonella to grow on the surface of the leaves.
Roughly 1.2 million Americans get a Salmonella infection each year and 450 of them die from it, according to the CDC. In a Q&A with Leicester University, the researchers called for higher food safety standards from salad leaf growers, which they hope could help decrease the likelihood of future outbreaks.
"Preventing enteric pathogen contamination of fresh salad produce would not only reassure consumers," co-author Giannis Koukkidis says, "but will also benefit the economy due to fewer days lost through food poisoning. We are now working hard to find ways of preventing salad-based infections."
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