According to Whole Foods Market, which last week recalled 48,000 pounds of presumptive contaminated meat that allegedly sickened customers in two states, the company is checking all ground beef supplies to make sure they come from processors approved by the seller.

Whole Foods, the world's largest retailer of natural and organic foods, is asking the processors to ensure in writing they are testing the suspect products for contamination by E. coli bacteria, which can cause serious food poisoning in humans, spokeswoman Libba Letton stated Tuesday.

Letton added that the company would also analyze the procedures for approving suppliers and checking the quality of products. “It’s going to mean going back and examining these other things and making sure there aren’t holes, especially in terms of food safety,” she said during an interview.

Coleman Natural Foods, the largest natural meat company nationwide, started using an Omaha slaughterhouse that had received various citations and had battled with the Agriculture Department, the New York Times informed. The U.S. government believes that the ground beef that triggered several people into falling ill had the source at the plant.

On Friday, 1.2 million pounds of the fresh ground beef it sold between June 2 and August 6 was recalled Nebraska Beef Ltd because it may have been tainted with the bacteria. This voluntary recall has led Whole Foods Market to tighten oversight of its food suppliers to keep poor quality products out of stores, the newspaper reported on its Web site.

Over the past few days, at least four local grocery chains, such as Fred Meyer and City Market, have also recalled possibly tainted beef.