Lancaster University

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Microbiologists investigate food safety

12/06/2006 16:50:10

PhD student Joanna Heaton examines watercress grown in the laboratory
PhD student Joanna Heaton examines watercress grown in the laboratory

Fruit and vegetables imported from abroad may be exposing consumers to a greater risk of illness according to experts at Lancaster University.

Ninety per cent of fruit and 29 per cent of vegetables are imported into the UK to meet the public’s demand for a healthy diet.

Dr. Keith Jones and PhD student Joanna Heaton from the Lancaster Environment Centre said: “There is concern that imported fresh produce may be more contaminated than home grown produce.”

Ninety-five people fell ill in the UK last year after eating lettuce contaminated with Salmonella. The lettuce was imported from Spain where farmers had used sewage effluent to irrigate the crop during a drought.

Two hundred people fell ill in the US earlier this year after eating spinach contaminated with E.coli157 from cattle manure in irrigation water. And in Florida, Salmonella associated with alligators and amphibians has even been found on tomatoes grown outdoors.

In the UK, around 40 per cent of food poisoning outbreaks linked to the consumption of fruit and vegetables are due to Salmonella.

The microbiologists decided to find out how safe fresh produce is in Lancaster by testing a range of fruit and vegetables bought from several shops. The results were reassuring – neither Campylobacter nor Salmonella were found on any of the samples. And although they found Listeria and Aeromonas on packaged organic watercress, these types of bacteria on fruit and vegetables rarely cause illness.

They said: “As animal manures are used as fertiliser for organically grown fruit and vegetables, the potential for microbial contamination is higher than for conventionally grown crops.”

Another cause of contamination is a lack of cooking and washing.

“Fruit and salad vegetables are different from most foods that we buy because they are not cooked and any disease-causing organisms present will be swallowed. The move towards pre-packed salads has made us careless about thoroughly cleaning fresh produce.”

But even washing cannot eradicate all contamination.

“Attached bacteria are difficult to wash off and it is generally accepted that approximately ten per cent are not removed by washing.

“Washing can also lead to the spread of bacteria – for example, if only one leaf of lettuce is contaminated, the washing process transfers bacteria to all the other leaves.”

Other causes of contamination include poor worker hygiene and flocks of wild birds in fields where crops are grown.

Their article on the “Microbial contamination of fruit and vegetables:evidence and issues” appears in the December issue of The Microbiologist.