According to the New York Times and Food Safety News, last month, Costco, one of the nation’s largest food retailers, quietly began requiring its suppliers of bagged produce, including salad greens and mixes, apple slices and baby carrots, to test for a broad range of toxic E. coli.

“We know this is where we have to go and there’s no reason to wait,” said Craig Wilson, the food safety director of Costco. In the last two weeks, he said, most produce suppliers have added a test that can detect the strain from the European outbreak as well.

The company also plans to test all of the ground beef sold at its warehouse stores. Costco operates a large ground beef plant in Tracy, Calif., and Mr. Wilson said the plant recently began evaluating testing procedures to detect the broader range of E. coli in the hamburger it makes and the beef trimmings that go into it. As an added step, the company plans to ask suppliers of the trimmings to do their own testing, starting later this summer, he said.

Until recently, the produce and beef industries focused E. coli prevention efforts on a single strain of the bacteria, known as O157:H7, which was responsible for scores of outbreaks and recalls.

But public health experts have identified six rarer forms, often referred to as the “Big Six,” which have increasingly been found to be the cause of illness related to food, including an outbreak in the United States last year traced to tainted romaine lettuce.

Costco’s new testing requirements come as the federal government continues to drag its feet on what to do about the expanding E. coli threat. After four years of study, the United States Department of Agriculture finished drafting rules in January for how the industry should handle the “Big Six” E. coli in ground beef. But the proposal has been stalled within the Office of Management and Budget, which reviews most federal regulations before they are released. Details of the proposal are confidential, but many in the industry expect that the rules would require testing or even make it illegal to sell ground beef that contained the additional strains of toxic E. coli.