Andrew Hancock

Dr Applegate on the hunt

FOOD scares can lead to widespread anxiety. Everyone has to eat and there is often no way of knowing whether a person has been affected by contaminated food before it is too late. Most of the bugs that give people food poisoning cannot be seen with the naked eye or detected by the nose or taste buds. Recent events in China, where milk was tainted with melamine, an industrial chemical, in order to conceal that it had been watered down, have caused some children to die and over 50,000 others to fall ill. That understandably made international headlines. But remember that people also suffer from infected food in almost every city, every day.

One of the most prevalent culprits is the bacterium Escherichia coli. Whereas most strains are harmless and can be found in the intestines of animals, one particular strain is very nasty. It can spread to beef, vegetables, unpasteurised milk and water, causing illness in people unlucky enough to ingest contaminated produce. In America alone, this strain may be responsible for as many as 70,000 infections each year, according to the Centres for Disease Control and Prevention, a government agency. And that could be a conservative estimate, since many of those infected do not seek medical attention.

There are ways of detecting this strain of E. coli, but they require growing up to 100m cells of the bacterium before it can be identified. This procedure can take more than 24 hours, by which time the infected food may have reached the consumer and the damage will have been done. Now, however, Bruce Applegate, an associate professor of food science at Purdue University in Indiana, has come up with a faster method of identifying the bug—one that may also prove less expensive.

Dr Applegate has tinkered with the genome of a virus that can infect the nefarious strain of E. coli, and which can be grown in an innocuous non-pathogenic laboratory-strain of the bacterium. When exposed to the disease-causing type, the virus attaches itself and turns the contaminated sample red, or it can “bioluminesce”—that is, emit light. Dr Applegate says his method can spot a single bacterium in just 25 grams of food, making it possible to detect an infection extremely quickly. Not only that, but it can also trap the bacteria, which can help companies carrying out food recalls to track the contaminant to its source.

Since most food companies already have instruments for measuring light so as to perform other tests, there is no need for new equipment. Dr Applegate has teamed up with Lynda Perry, his research associate, to found Intelliphage, a start-up company, to develop and commercialise his discovery. They are also looking at how it could be extended to detect other virulent microbes, including salmonella, listeria, staphylococcus and Mycobacterium tuberculosis. Food scares may not be a thing of the past just yet, but at least bacteria now have reason to fear.

http://www.economist.com/science/tm/displayStory.cfm?story_id=12374591