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Poison-proof dairy products 'on sale in five years'

YOGHURTS and soft cheeses that kill food-poisoning microbes before they can grow could be on supermarket shelves within five years, scientists said yesterday.

Researchers have manipulated the genes of the harmless lactic acid bacteria used to ferment dairy products so they produce a toxin that destroys listeria - a food poison that has caused many deaths. The hope is that badly stored yoghurts or cheeses that would normally be prone to listeria infection would be able to fight off attack as their own harmless bacteria begin to grow.

Scientists at the Norwich laboratory of the Institute of Food Research say the research is in its infancy and that it needs both commerical exploitation and approval from regulatory authorities before the breakthrough could be incorporated into products.

Mike Gasson, head of genetics at Norwich, said that with adequate funding it may be possible to develop listeria-destroying dairy products within five years, although 'it's still at the laboratory stage'. He and his colleagues have already produced genetically modified lactic acid bateria that produce a toxin which destroys listeria. 'It's incredibly powerful in its effect,' he said.

The toxin occurs naturally in viruses that specifically attack and infect listeria. It was an enzyme that dissolved the cell wall of the microbe, Professor Douglas G eorgala, director of the institute, said.

The scientists identified the gene responsible for the toxic enzyme and inserted it into lactic acid bacteria. 'It's now shown to be feasible to find the genes that can smash up listeria,' he said.

'In live dairy products you would be using a living organism as a fail-safe if something went wrong.' The scientists also hope to design food that can fight against infection with salmonella bacteria. He added: 'You'd have to design a separate method. We've not yet done that.'

Professor Georgala has contributed to a report on new developments in food and agricultural biotechnology, published by the Organisation for Economic Cooperation and Development, which describes other potential uses for genetically manipulated lactic acid bacteria.

It says they may be used as preservatives outside the traditional area of fermented food: 'It may well be that these lactic bacteria incorporated in a food could provide a fail-safe capacity, whereby if the food was abused by storage at the wrong temperature or for too long, the special lactic bacteria would grow and provide specific protection against undesirable food poisoning bacteria such as the listeria or botulinum.'