USDA researchers say grilling steaks which have been "blade tenderized" still kills E. coli.

It's well known that grilling kills E. coli on meat surfaces. That's why steaks can be safely cooked rare or medium rare while ground beef products must be cooked to a higher internal temperature.

But when steaks such as the top sirloin are punctured with a series of blades to break the fibers and make them more tender there's concern E. coli pushed inside the steak may not be killed. Blade tenderization is a common industry practice on lesser quality steaks which are popular as discount restaurant items. In fact, blade tenderization is becoming more common in the retail grocery cases, as well as in food service.

To that end, USDA-ARS microbiologist John B. Luchansky and his colleagues in Pennsylvania are conducting experiments to ascertain whether Escherichia coli O157:H7 of any of its pathogenic relatives might pose a danger with this practice.

In early studies, the researchers applied various levels of E. coli O157:H7 to the "lean-side" surface of subprimals, ran the meat lean side up through a blade tenderizer, and then took core samples from 10 sites on each subprimal to a depth of about 3 inches.

In general, only 3-4% of the E. coli O157:H7 cells were transported to the geometric center of the meat. At least 40 percent of the cells remained in the top 0.4 inch.

Next, the group applied E. coli to the lean-side surface of more subprimals, put the meat through a blade tenderizer, then sliced it into steaks with a thickness of three-fourths of an inch, 1 inch, or 1.25 inches. Using a commercial open-flame gas grill, they cooked the steaks on both sides to an internal temperature of 120 degrees Fahrenheit (very rare), 130 degrees F (rare), or 140 degrees F (medium rare).

The findings confirmed that if a relatively low level of E. coli O157:H7 is distributed throughout a blade-tenderized top sirloin steak, proper cooking on a commercial gas grill is effective for eliminating the microbe.