By Sharon Omahen

University of Georgia

University of Georgia scientists have found bacteria that kill
listeria in processing plant floor drains, where the pathogen is
known to settle and multiply.

“There are just a few thousand cases of listeria in humans
each
year,” said Michael Doyle, a microbiologist and director of the
UGA
Center for Food Safety in Griffin, Ga. “But, of those, about 500
die. That’s a high mortality rate, and that’s why listeria
infections are a major concern in our country.”

Pregnant women, cancer patients and transplant patients are
among
the most frequent cases seen. “Listeria strikes these
immunocompromised populations hardest,” Doyle said.

Luncheon meats = high risk

The U.S. Department of Agriculture identifies luncheon meats
as
high-risk products for listeria infections, Doyle said. Sliced
turkey deli meats are high on the list.

“Listeria can grow to billions of cells in some refrigerated
luncheon meats,” he said. “And there have been major outbreaks
traced to sliced turkey luncheon meats.”

The deadly pathogen is often found in processing-plant floor
drains. To help fight it, representatives of the processed meat
industry asked Doyle and his UGA colleagues to help find a
solution.

“Listeria can be widely distributed in processing plants,”
Doyle
said. “It grows where there is water in areas like floor drains,
where listeria can set up a home.”

Unfortunately, floor drains are one of the toughest areas to
effectively clean and treat for listeria in processing
plants.

Biofilm forms protective coating

“Over time, a biofilm, or slime layer, develops in the
drains,”
Doyle said. “This biofilm protects the listeria when cleaners and
sanitizers are poured down the drains.”

Knowing this, Doyle took a fight-fire-with-fire approach to
killing
the drain-dwelling listeria. He uses the same technology he
developed for controlling E. coli and Salmonella.

“We took samples of biofilm from floor drains in processing
plants
where there was a history of low levels to no listeria,” he
said.

With the help of the plant operators, biofilm samples were
taken
from dairy, poultry and infant food processing plants. The
scientists found nine different bacteria from biofilms that were
highly effective in competing with and killing listeria.

“From these bacteria, we chose two strains that could grow
with
listeria and ultimately outcompete it,” Doyle said.

The researchers then tested these two strains in a fresh
poultry
processing plant. Working with Ecolab Inc., UGA scientists used a
foaming agent to apply the bacteria to drains.

“The foam adheres to the drain’s surface and gives the good
bacteria an opportunity to attach and grow in their new
environment,” Doyle said.

Foam/biofilm mixture successful

The drains were monitored for more than three months. The
foam/biofilm mixture eliminated listeria in most drains to
undetectable numbers for several weeks.

“In some drains, where there was a continuous influx of
processing
wastes, we were able to bring the numbers down dramatically,”
Doyle
said, “but we couldn’t totally eliminate the listeria.”

Next, the UGA researchers tested the bacteria mixture in a
ready-to-eat deli meat processing plant. The listeria numbers
are much
lower in these plants than in fresh meat plants.

Six drains were treated, and two were used as natural control
drains. After eight weeks, the scientists found five of the six
treated drains were free of detectable listeria.

Ecolab has licensed this technology from UGA and is
developing a
formulation that will be further tested. The company intends to
make the product commercially available after regulatory review
and
approval.