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Bug busters

作者:莫樘    发布时间:2019-03-08 06:13:02    

By Andy Coghlan VIRUSES that rip bacteria apart have been harnessed in a new test that can reveal dangerous bacteria in blood, pharmaceuticals and food. The test was jointly developed by scientists at the Defence Evaluation and Research Agency lab at Porton Down in Wiltshire and the Ministry of Agriculture, Fisheries and Food’s Central Science Laboratory in York. Melenie Murphy, a senior scientist in the DERA team, says that the viral test can pinpoint contaminated food in eight hours—compared with the two to three days it currently takes to grow colonies of bacteria from samples. “Our aim is for a test which goes from sample to answer within eight hours, even if as few as 100 bacteria are present,” she says. The test has two major components. The first is a bacteriophage, a virus harmless to people but lethal to specific strains of bacteria. By selecting the right bacteriophage, the researchers can tailor the test to spot particular types of bacteria. The second component is luciferase, the enzyme which creates the glow in the tails of fireflies. Suitable bacteriophages are readily available in the environment. “You just go to the local sewage works and pan for what you’re looking for,” says Murphy. In the test, unveiled last week, the blood, drug or food sample is mixed with bacteriophages which are known to detect a target organism such as Salmonella enteritidis, which causes severe food poisoning. Once the phages have invaded cells of S. enteritidis, they multiply and burst out, breaking open the cell wall within 40 minutes and spilling its contents into solution. When luciferase is added to the mixture, it reacts with adenosine triphosphate (ATP) which has leaked from the burst cells. This produces a characteristic yellow glow, but not enough ATP oozes out to give a glow strong enough for detection. So to make the light brighter, the researchers add adenosine diphosphate (ADP). An enzyme called adenylate kinase, which also oozes out of the burst cells, converts this to ATP (see Diagram). The result is a glow 40 times brighter than that created by the original ATP alone. Since the researchers began their project in January, they have detected both S. enteritidis and Escherichia coli using the test. They now plan to turn it into a commercial system. Meanwhile, a home food-poisoning tester that uses different principles to DERA’s is being developed by Matsushita of Japan (This Week, 10 April, p 6). In two to three years, the company hopes to detect food-poisoning bacteria in just 10 minutes. But Matsushita’s system also detects harmless dead cells which may have been killed by pasteurisation, says Murphy,

 

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