Bagged salad linked to salmonella risk
Bags of prepared salad can provide the perfect breeding ground for bacteria that cause salmonella, according a study.
Juice from broken leaves can boost the growth of salmonella bacteria by more than 2,400-fold, scientists at the University of Leicester discovered.
The juices enabled the salmonella to attach itself to the salad leaves so strongly that even vigorous washing was not enough to remove the bacteria.
The salad can also increase the bacteria's virulence, making it more likely to cause an infection.
Experts warned consumers to avoid ready-cut salad if possible, to rinse bagged salad thoroughly, and not to let it get warm.
The scientists did not measure levels of salmonella in bought salad but investigated the way the bacteria grew on damaged leaves and attached itself to plastic bag surfaces.
Lead scientist Dr Primrose Freestone, from the University of Leicester's Department of Infection, Immunity and Inflammation, said: "Salad leaves are cut during harvesting and we found that even microlitres 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.
"Even small traces of juices released from damaged leaves can make the pathogen grow better and become more able to cause disease."
She said the research, published in the journal Applied and Environmental Microbiology, also served as a reminder to consume bagged salad as soon as possible after opening.
"We found that once opened, the bacteria naturally present on the leaves also grew much faster even when kept cold in the fridge," Dr Freestone added.
Dr Kimon Karatzas, Assistant Professor in Food Microbiology at the University of Reading, said: "Avoiding fresh produce is not a solution, but if possible, it would be preferable to buy uncut fresh produce over chopped, and to always wash it before you eat - even the ones that are already washed.
"Furthermore, keeping these foods in the refrigerator is important."