“The tests don’t make the food safer, but they do tell us if the vendors’ food safety programs are working.”

So says Craig Wilson, Costco’s vice president of quality assurance and food safety as he told The Packer that the company began requiring its produce suppliers to test finished products for the “Big 6” E. coli strains “a couple of months ago.”

He said the company added the rare strain O104:H4 that recently sickened more than 3,900 people in Europe to its mandatory test list “in the past two or three weeks.”

A related story in The Packer reports that neither Wal-Mart Stores Inc. nor Supervalu Inc. require the tests. Rather, both companies rely on Global Food Safety Initiative certifications and good agricultural practices requirements to make sure their customers are buying safe produce.

“No sampling can prevent, nor ensure, the absence of pathogens in produce,” said Wal-Mart’s vice president of food safety Frank Yiannis. “That’s why Wal-Mart and Sam’s Club … require our produce suppliers to achieve prevention-based certification using one of the GFSI internationally recognized food safety standards.”