Broken leaves in bags of prepared salad may dramatically increase the risk of salmonella, a study has shown. 
Juice from damaged leaves can boost growth of the food poisoning bug more than 2,400-fold, scientists discovered. 
It also has the effect of increasing 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." "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."

Source: QNA