When you hear the term “food poisoning” it usually conjures up images of hurried journeys to the toilet and rueful reviews while there of what was eaten the previous day. Most of the blame might be levelled at your meat main course – was the chicken undercooked or the steak too rare?
However, reports from the food safety community are increasingly suggesting we need to look elsewhere for the source of food poisoning outbreaks. Increasingly, suspicions are now that the side salad that garnished your suspect meat course may have contained more than just dietary fibre.
Research is showing that green leafy salads containing lettuce and spinach are subject to colonisation by food poisoning bacteria, most frequently Salmonella, E. coli and Listeria. In 2014, beansprouts contaminated with Salmonella infected more than 100 people in the US, a quarter of whom were hospitalised. In February 2016, more than 50 people in Victoria, Australia developed salmonellosis after eating bagged salad leaves, while in July 2016, 161 people fell ill in the UK after eating mixed salad leaves and two people died. The EU league table of sources of food poisoning outbreaks now ranks green salads as the second most common source of food-borne illness.
Foods such as salad leaves pose a particular infection risk because they are usually minimally processed after harvesting and consumed raw. Consequently, it isn’t surprising that considerable research effort has been made into improving the microbial safety of salad leaf culture as well as optimising protocols for processing and packaging.
But outbreaks still occur with devastating consequences and thus far very little has been known about what happens to the behaviour of food poisoning bacteria when in the actual salad bag – until now.
In our latest study, we concentrated on Salmonella as it is an aggressive pathogen that has been implicated in salad-associated infections. We found that juices released from the cut-ends of the salad leaves enabled the Salmonella to grow in water, even when it was refrigerated – this was a surprise as Salmonella has a temperature preference of 37C.