Walmart and health officials are waiting for the test results on a batch of powdered infant formula that was removed from more than 3,000 stores nationwide.
The formula was removed after a Missouri newborn who had consumed it died from a rare infection.
This type of bacteria occurs naturally in the environment and in plants such as wheat and rice. But it has also appeared in dried milk and powdered formula, so manufacturers routinely test for it.
Walmart pulled the Enfamil Newborn formula as a precaution after the death of Avery Cornett in the southern Missouri town of Lebanon. The government hasn't ordered a recall, and the manufacturer says test showed the batch was negative for the bacteria before it was shopped.
A second Missouri infant became ill after consuming powdered baby formula in the past month, but that child recovered.
The product isn't just sold at Walmart. The manufacturer, Mead Johnson Nutrition, hasn't said how widely it was distributed to other stores.
A spokesman says the company is "highly confident in the safety and quality" of its products.
Walmart says it has pulled a batch of powdered infant formula from stores nationwide after a newborn Missouri boy became gravely ill with a suspected infection and died after being taken off life support.
Walmart spokeswoman Dianna Gee said Wednesday the move is cautionary as health officials investigate Sunday's death of 10-day-old Avery Cornett of Lebanon, Mo.
No government recall has been ordered for the 12.5-ounce cans of Enfamil Newborn powder with the lot number ZP1J7G.
Media reports say Avery received a preliminary diagnosis of infection from a rare bacterium called Cronobacter sakazakii.
The formula's manufacturer, Mead Johnson Nutrition, says the batch Walmart pulled tested negative for the bacterium. Spokesman Christopher Perille says numerous companies sell the formula, though it's unclear if others sold from that batch.