At its Augusta, GA factory, Kellogg makes many of its baked products — including Keebler, Famous Amos and Murray cookies, as well as Kashi and Mother’s brand products.

The plant was also growing Listeria monocytogenes, a bacteria that can cause serious  illness and sometimes death.

That was in February, when the U.S. Food and Drug Administration (FDA) inspected the Augusta bakery that employs more than 500 people. FDA did environmental sampling that came back positive for Listeria monocytogenes in 15 locations, including some food contact surfaces.

Kellogg then shut down the plant for cleaning and made floor and roof repairs.

In a June 7 warning letter to John Bryant, chief executive officer of the Kellogg Company, FDA said the environmental sampling proved Listeria was “established in niche areas” inside the Georgia plant.

The warning letter was released Tuesday.

Listeria contamination was found along food contact surfaces including the conveyor mesh and belt of the spiral cooler in the production line. Analysis using Pulsed Field Gel Electrophoresis (PFGE) showed a pattern that was indistinguishable from the environmental samples collected in the plant. FDA found it highly likely the same strain was being transported throughout the facility.

Kellogg, which issued a statement Tuesday saying food safety was of “utmost importance” to the company, has met with FDA officials in both Atlanta and Silver Springs, MD since the Listeria problem was discovered. It has also twice written FDA about corrections at the Georgia plant.

A request by Food Safety News for a copy of Kellogg’s written response to the warning letter went unanswered.

Problems inside the plant cited by FDA may be contributing to the problem, included drips or condensate from pipes, causing water to pool and potentially contaminate food surfaces.  Flies were seen around drains and a flour mixer.

Kellogg promised to remove pipes to control the dripping problem and to use pressurized aerosol insecticide on the flies.

FDA said it would determine at its next inspection whether the steps taken by Kellogg  are sufficient. In the meantime, FDA gave the company 15 working days to respond to the warning letter with documentation.

“We have undertaken a number of aggressive action to address their (FDA) concerns, including comprehensive cleaning and extensive testing, and have confidence in the safety  of our food,” said Kris Charles, Kellogg spokeswoman.

Listeria can be very difficult to eradicate once the pathogen takes hold inside a food plant. Maple Leaf Foods in Toronto found that out three years ago when its failure to eradicate Listeria led to a nationwide outbreak linked to deli meats that killed 22 mostly elderly Canadians.

Two years ago, local development authorities in Georgia provided $30 million in tax-exempt bond financing for improvements at the Kellogg’s facility in Augusta. The Battle Creek, MI-based company also made fairly recent investments in $5 million worth of equipment relocated to the former Murray’s Biscuits plant.

Kellogg Company sales totaled more than $12 billion last year. It has manufacturing facilities in 18 countries and markets products in more than 180 counties. Problems at some of its U.S. plants last year led to a shortage of its popular Eggo frozen waffles and several popular cereals had to be recalled over packaging problems.