A joint U.S.-Canadian investigation matched the DNA fingerprint of E. coli O157:H7 bacteria isolated from beef trim that had remained in storage with Rancher's Beef Ltd. to samples taken both from victims of the food poisoning outbreak and packages, both intact and opened, of Topps Meat Co. frozen hamburgers. Rancher's Beef of Balzac, Alberta, had supplied Topps with beef trim used to make the patties, the USDA said.

A message left with Rancher's Beef, which has ceased operations, was not immediately returned.

Topps, based in Elizabeth, N.J., recalled in September all frozen patties it had made in the previous 12 months - 21.7 million pounds - in what is the second-largest beef recall in U.S. history. Topps too shut down just days later.

The massive recall prompted the Agriculture Department to announce changes in how it will inspect meat plants. After being criticized for foot-dragging, the USDA said it would move faster to encourage recalls. The agency cannot issue recalls.

E. coli is harbored in the intestines of cattle. Improper butchering and processing can cause the E. coli to get onto meat. Thorough cooking, to at least 160 degrees internal temperature, can destroy the bacteria.