For the first time in this country, public health officials have linked ground beef to illnesses from a rare strain of E. coli, adding fuel to an already fierce debate over expanding federal rules meant to keep the toxic bacteria out of the meat supply.

Cargill Meat Solutions recalled 8,500 pounds of hamburger on Saturday after investigators determined that it was the likely source of a bacterial strain known as E. coli O26, which had sickened three people in Maine and New York.

Under federal rules, it is illegal to sell ground beef containing a more common strain of the bacteria, E. coli O157:H7, which has been responsible for thousands of illnesses, many deaths and the recall of millions of pounds of beef over the years. But federal regulators are now considering whether to give the same illegal status to at least six other E. coli strains, including O26, which can also make people violently sick.

The meat industry has opposed such a change, saying it is not needed. Among the arguments the industry has used was one stubborn fact: no outbreak in this country from the rarer strains of E. coli had ever been definitively tied to ground beef.

The industry can no longer make that argument.

“It might act as a catalyst,” James Marsden, a professor of food safety and security at Kansas State University, said about the outbreak and recall. “Clearly it’s back on the front burner, that’s for sure, and clearly U.S.D.A. is under pressure.”