[ti:New Genetic Test Helps Find Food Poisoning] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:00.00]American scientists are using genetic markers [00:04.46]to investigate food poisoning cases linked to romaine lettuce. [00:09.66]The Associated Press reports that their use of genetic sequencing [00:15.54]is completely changing the discovery of bacteria in food. [00:20.79]Genetic sequencing is being used to strengthen investigations and, [00:26.82]in some cases, find links between what once seemed to be unrelated diseases. [00:33.48]The technology also is uncovering once unknown causes of food poisoning. [00:41.01]One such example involved apples covered in caramel, [00:46.21]a popular treat in the United States. [00:49.13]Up to now, scientists have been looking mainly at one bacteria: listeria. [00:57.02]But the search is expanding. [01:00.15]By the end of this year, laboratories in all 50 states are expected to [01:07.05]also be using genetic sequencing for more common causes of food poisoning. [01:13.90]That includes salmonella and the E. coli bacteria linked to the romaine lettuce outbreak. [01:21.50]The new technique is also helping disease scientists [01:25.78]identify food contamination even before it causes people to get sick. [01:32.05]Lawyer Bill Marler has taken companies to court when their food products sicken people. [01:39.47]He said the technique is changing how outbreaks are discovered. [01:44.72]Marler said the testing program is still young. [01:48.95]He said it is too early to call genetic sequencing a success. [01:54.62]But he said it may change how and when outbreaks are found. [02:00.79]The Centers for Disease Control and Prevention, or CDC, supports the program. [02:08.26]It estimates that 48 million Americans get sick from food poisoning each year. [02:15.91]And 3,000 of those people die from such infections. [02:20.98]The use of genetic sequencing involves something called whole genome sequencing, [02:28.19]which has been used in biology for more than 20 years. [02:32.76]A genome is a kind of genetic map. [02:36.86]It contains all of the genetic information, or DNA, about an organism. [02:44.57]DNA is short for the term deoxyribonucleic acid. [02:51.07]The laboratory process identifies most of an organism's DNA. [02:57.03]And scientists use computer programs to compare the DNA of test specimens to see [03:05.57]if they are the same as the organism and how resistant they are to current medicines. [03:11.81]The technique makes the lab studies faster, less costly and more automated, [03:19.34]said Robert Tauxe, one of the CDC's leading experts on food poisoning. [03:25.81]Plans are to use the technology against several bacteria that cause food poisoning. [03:33.28]But to date, all of the tests have involved listeria. [03:38.61]The bacteria causes around 1,600 cases of food poisoning nationwide each year. [03:47.70]But it is a very deadly infection, killing nearly one in five people who get it. [03:55.41]It can take weeks for people to develop signs of the disease. [04:00.56]In the past, some patients died by the time health officials began to recognize the problem. [04:07.82]For nearly 15 years, from 1983-1997, only five listeria outbreaks were identified in the United States. [04:20.28]They were relatively large, with an average of 54 cases for each outbreak. [04:27.85]That is how it was with other food poisoning outbreaks. [04:32.48]Tauxe said most foodborne outbreaks were found because they happened in one place, [04:39.27]like a town with a popular eatery where people became sick. [04:44.08]Outbreaks were studied by asking people what they ate before they got sick. [04:51.36]Investigators then compared notes to see what patients had in common. [04:58.13]But the science took a big step in the 1990s, [05:03.02]after a major outbreak happened in the Seattle, Washington area. [05:07.72]Four deaths and more than 700 other infections eventually were linked [05:15.27]to undercooked hamburgers from a Jack in the Box restaurant. [05:19.71]The meat contained the bacteria E. coli. [05:23.57]The outbreak led the CDC to develop a program [05:28.80]that used a technique called pulsed-field gel electrophoresis. [05:35.83]With this, investigators could look at a bacteria's DNA in parts. [05:41.89]The program helped health officials more easily link cases. [05:47.40]But it was not perfect. It was unable to make exact matches [05:54.76]and sometimes missed when cases were related. [05:58.45]Then came whole genome sequencing. [06:02.26]The CDC began using the technique in food poisoning investigations in 2013. [06:10.33]In the beginning, state laboratories sent samples to a CDC laboratory in Georgia for testing. [06:18.88]Now, the CDC is working to make the technology available in all 50 states. [06:26.63]I'm Alice Bryant.更多听力请访问51VOA.COM