The growing popularity of pre-packed salads is likely to lead to an increase in food poisoning cases, scientists warned yesterday.

They said the increased uptake in the salads in particular, but also in fruit and vegetables, is likely to be reflected in a future rise in food poisoning.

They also warn that while scientists have a role to play in developing technology to protect food from contamination, consumers should be aware of the risks.

The comments were made ahead of a discussion of research into food contamination at a conference in Aberdeen today.

Led by Imperial College London, the research details how salmonella bacteria are able to contaminate salads and vegetables.

Professor Gadi Frankel, from Imperial College, said a greater understanding of how salads are contaminated is important because cases of food poisoning caused by salads are "likely to rise in the future".

He said there had been recent outbreaks that could specifically be related to pre-packed salads, including a salmonella outbreak in the UK last year traced to imported basil and an E.coli outbreak in the US in 2006 traced to pre-packed baby spinach.

He said: "In their efforts to eat healthily, people are eating more salad products, choosing to buy organic brands and preferring the ease of pre-washed' bagged salads from supermarkets, than ever before.

"All of these factors, together with the globalisation of the food market, mean that cases of salmonella and E.coli poisoning caused by salads are likely to rise in the future.

"This is why it's important to get a head start with understanding how contamination occurs now."

He said that a label stating food was pre-washed did not necessarily mean it was safe to eat and, although the risk of poisoning remained low, consumers should make "informed decisions".

He said: "There are many kinds of salad bags being marketed as washed and ready-to-eat. It is about individual choice, but people should be aware of the risks so they can make informed decisions about whether they want to wash their food or not."

Food poisoning from salmonella and E.coli is commonly associated with eating contaminated bovine or chicken products.

The germs live in the guts of cows and egg-ducts of chickens, and contamination of meat can occur during slaughtering, but recent outbreaks of food poisoning highlight the dangers associated with contaminated salad or vegetables.

Professor Frankel's research found that salmonella bacteria are able to use their flagella - the stringy "propellers" which aid their movement - to grip salad leaves.