Study: Damaged Leaves Stimulate Salmonella Growth In Bagged Salad
PHILADELPHIA (CBS)—Those ready-to-eat bags of salad you may be enjoying could be actually enhancing the presence of the food poisoning bug Salmonella, a new study in the UK suggests.
Researchers at the University of Leicester have discovered that juices released from damaged leaves also had the effect of enhancing the virulence of the pathogen, potentially increasing its ability to cause infection in the consumer.
"Salad leaves are cut during harvesting and we found that even microliters of the juices (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," said Dr. Primrose Freestone of the University's Department of Infection, Immunity and Inflammation. "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."
Primrose strongly emphasized 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 be become many thousands by the time a bag of salad leaves reaches its use by date
"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 present on the leaves also grew much faster even when kept cold in the fridge," Primrose said.
PhD student Giannis Koukkidis, who has been funded by a Biotechnology and Biological Sciences Research Council (BBSRC) i-case Studentship says despite a number of published reports on improving the microbiological safety of salad leaf production, very few studies have investigated the behavior of Salmonella once the leaves have been bagged.
"Anything which enhances adherence of foodborne pathogens to leaf surfaces also increases their persistence and ability to resist removal, such as during salad washing procedures," said Koukkidis. "Even more worrying for those who might eat a Salmonella contaminated salad was the finding that proteins required for the virulence (capacity to cause infection) of the bacteria were increased when the Salmonella came into contact with the salad leaf juices. Preventing enteric pathogen contamination of fresh salad produce would not only reassure consumers 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."
There are more than 500,000 cases of food poisoning a year from known pathogens in the UK, according to a report out by the Food Standards Agency. While poultry meat was the most common source of infection, some 48,000 of food poisoning cases were from fresh produce: vegetables, fruit, nuts and sprouting seeds.
READ MORE on the study here.