Preventing listeria outbreaks at produce facilities |

Preventing listeria outbreaks at produce facilities

Listeria is a hard bacteria to find, and when it comes to food safety, it can be a nightmare.

During the Colorado Fruit and Vegetable Grower's Association annual conference in February, Laura K. Strawn spoke to a group about ways fruit and vegetable growers can manage and prevent listeria outbreaks.

Strawn is a Virginia Tech Extension specialist and focuses on food science and technology.


Strawn suggested carving out four zones in a facility, based on where produce directly and indirectly touches. She said there should be four zones:

Zone one for areas produce directly touches. This would be conveyer belts, shoots, buckets, etc.

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Zone two for areas produce comes close to but doesn't necessarily touch. This could be the sides of the conveyer belts, the outside of buckets or under equipment used to move produce.

Zone three for areas where produce goes through, but might not be directly touching. This could be walls or the tires on a forklift.

Zone four is for places within a facility where produce shouldn't go through at all, which could include a break room for employees.

The zones are important because they set up a way to test for listeria and nip it in the bud.

When it comes to cleaning, zone one and two should be the first priority. Those are the areas that should be cleaned most thoroughly and not rushed.

"You don't want to rush your sanitation," Strawn said. "You want the time built in to give proper sanitation."

Strawn recommended testing first in zones four or three before testing in two or one. If listeria has made it to zone four or three, chances are there is listeria in the facility, but if a company finds it early enough in zone three or four, it gives them a heads up without needing to shut down operations.

Once detected, the cleaning must start right away.


When assessing risk for listeria, there are a few obvious places to keep in check and a few places most wouldn't think listeria would hide.

Listeria is a tricky bacterium as it is easily adaptable and can spread in a wide range of temperatures.

If listeria is around, it can easily adapt and spread. That's why it's so important to take the time to clean the areas the produce touches thoroughly.

Strawn said drains and areas with standing water are places listeria thrives. Shoes or tires are ways the bacteria can spread throughout a facility, which is why it's so important to continuously clean and test for listeria in zones.

When it comes to drains, Strawn recommended keeping them away from walls, if possible. The intersection between the wall and the floor are places listeria can thrive.

"Listeria likes cold, dark, wet areas. … That's where it likes to be," she said.

It can even be in places one might not consider, such as inside of a screw head. Floor mats also are a tricky area. Once they're contaminated, Strawn said it's better to just replace them.

"All things hollow are a risk," she said.

— Fox is a reporter for The Fence Post. She can be reached at, (970) 392-4410 or on Twitter @FoxonaFarm.