A Quick DNA Test Seeks Out A Dangerous Bacteria That Lurk In Food

February 24, 1999

THE number of cases of food poisoning could be dramatically cut now that US government researchers have developed the first simple test for the bacterium Campylobacter. In another breakthrough, scientists have developed a scanner that can reveal whether cattle carcasses are contaminated with faeces that could cause disease.

Every year, millions of people in the industrialised world come down with food poisoning caused by Campylobacter. It affects four times the number of people stricken by the better-known Salmonella. Yet until now, there has been no quick or reliable test for Campylobacter in livestock or food.

"Campylobacter has not had the attention of other food-poisoning bacteria," says Irene Wesley of the National Animal Disease Center (NADC) in Ames, Iowa. "It is hard to grow in the lab, and while it makes more people sick than, say, Salmonella, it kills less frequently." However, Campylobacter is thought to cause between 20 and 40 per cent of cases of Guillain-Barr? syndrome, a severe neural disorder that can make people so weak they may need help breathing.

Until now, diagnosing Campylobacter infections or identifying the bacterium in food involved weeks of culturing, and the methods used to distinguish the most dangerous species were unreliable. But Wesley and her colleagues have solved both problems with a test that uses the polymerase chain reaction to amplify Campylobacter's DNA. The test takes only eight hours to complete and can reliably identify the worst culprit, C. jejuni, as well as several other species.

The first trials of the test have revealed that 39 per cent of healthy dairy cattle in the US carry C. jejuni in their faeces, which can contaminate milk and carcasses at slaughter. It is also present in the faeces of up to 70 per cent of healthy adult pigs and 90 per cent of piglets.

The researchers say they are comparing the two main methods for intensively raising pigs-keeping a barn occupied continuously or periodically emptying and cleaning it-to see which leads to most infection with Campylobacter. They are also trying to develop an even simpler test for the bug that could be used by farmers to detect and treat early infection.

But the key to preventing food poisoning with Campylobacter and many other bacteria, says Wesley, is preventing faecal contamination of meat. To this end, Mark Rasmussen of the NADC and his colleagues have developed a scanner that emits light at a wavelength that makes several bacteria found in cattle faeces fluoresce. Contaminated areas show up as green spots on the carcass, which can then be trimmed or cleaned.

Rasmussen says he is looking for a commercial partner to develop the scanner and produce a simpler, hand-held instrument.
Author: Debora MacKenzie
New Scientist issue 27th Feb 99

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New Scientist

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