WASHINGTON — The Food and Drug Administration earlier this month issued a warning letter to The Kellogg Co. after an inspection of the company’s cookie plant in Augusta, Ga., between January 2010 and February 2011 was found to have “a persistent strain” of Listeria monocytogenes.

The letter, dated June 7, comes less than two years after Kellogg’s Eggo waffle plant in the same state was shuttered for similar reasons.

The F.D.A. said 15 environmental swabs were positive for the Listeria monocytogenes pathogen, with 7 of the swabs taken from direct food-contact surfaces such as the conveyor mesh and belt of the spiral cooler in a production line.

“The presence of a persistent strain of L. monocytogenes in your facility between January 2010 and February 2011 is significant in that it demonstrates that your cleaning and sanitation efforts were inadequate to remove this organism,” the F.D.A. said. “We note that although your finished product cookies may not support the growth of L. monocytogenes, the positive environmental swabs are indicators of insanitary conditions in your facility and demonstrate a failure of cleaning and sanitation operations that may allow for contamination of foods with filth or pathogens.”

The F.D.A. said it received a response from Kellogg dated March 9 outlining corrective actions the company has taken at the facility, including detailed cleaning and fogging activities. The F.D.A. said it will evaluate the implementation and effectiveness of the corrective actions at its next inspection.

“The safety of our food is of utmost importance to Kellogg,” said Kris Charles, a spokesperson with Kellogg. “While the F.D.A. did not identify specific concerns with the food, we take this situation very seriously. We have undertaken a number of aggressive actions to address their concerns including comprehensive cleaning and extensive testing. We have confidence in the safety of our food.”