Investigations by University of Leicester microbiologists, supported by BBSRC, have revealed that juices released from damaged leaves can enhance the virulence of Salmonella, potentially increasing its ability to cause infection in the consumer.
Dr Primrose Freestone, who led the work, said, “Salad leaves are cut during harvesting and we found that even less than 1/200th of a teaspoon which leach from the cut-ends of the leaves enabled Salmonella to grow in water, even when it was refrigerated. These juices also helped the Salmonella to attach itself to the salad leaves so strongly that vigorous washing could not remove the bacteria, and even enabled the pathogen to attach to the salad bag container.
“This strongly emphasises the need for salad leaf growers to maintain high food safety standards as even a few Salmonella cells in a salad bag at the time of purchase could become many thousands by the time a bag of salad leaves reaches its use by date, even if kept refrigerated.
“It also serves as a reminder to consume a bagged salad as soon as possible after it is opened. We found that once opened, the bacteria naturally on the leaves also grew much faster even when kept cold in the fridge.”
However, she also stressed that, “This research did not look for evidence of salmonella in bagged salads. Instead, it examined how Salmonella grows on salad leaves when they are damaged.” Leafy salad crops can be exposed to Salmonella, via insects, bird poop, and manure, among other sources and while such outbreaks are uncommon, they remain a problem. Dr Freestone added that outbreaks may occur despite practices used to mitigate the problem.
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