Swabbing for Listeria
See an MPI demonstration video showing how to collect environmental samples for Listeria testing.
Collecting environmental samples
This video is for Risk Mangement Programme (RMP) operators who need to create an environmental testing programme. In this demonstration, you can see how to collect environmental samples from a processing area. These samples can then be tested for Listeria.
[Computer rendered image of Listeria. Typing can be heard as text appears on screen.]
Narrator: Listeria is a harmful bacteria that can cause illness and death.
Unfortunately, in New Zealand, people have died following the consumption of ready-to-eat foods contaminated with Listeria.
As a food processor, you can be prosecuted if people get sick or die from listeria-contaminated food.
Food often gets contaminated with Listeria in the processing environment.
Learn how to minimise the risk by developing a Listeria Management Plan and environmental swabbing.
[High-risk areas for Listeria contamination and growth are shown.]
Listeria is frequently isolated from inside food factories where there’s usually plenty of food and moisture to enable them to grow to very high numbers.
It's really important to control Listeria in food factories to minimise the chances of Listeria contaminating food.
Floors and drains are most likely to become contaminated with Listeria.
Think about it, anything and everything could fall onto the floor. Cracks and holes in the floor provide excellent places for Listeria to live and grow.
And it doesn’t take much to spread to food contact surfaces.
[Comical music plays as clumsy butcher drops scoop on to floor, before wiping scoop on pants and continuing to work. A red bar symbol is displayed, indicating that this is dangerous practice.]
Cross contamination is a real problem for ready-to-eat foods. That’s the bad news.
No-one likes getting sick, so what can we do about it?
[Shots of clean and secured processing area. A butcher prepares for entering the processing area by dressing in protective clothing and washing hands.]
Well, every manufacturer of ready-to-eat foods needs a Listeria Management Plan.
This includes such things as making sure the building is secure to keep out pests like rodents and insects.
Controlling how things are taken into the processing area. Including controlling what people wear and how they enter the processing area.
Hopefully, the precautions taken to keep Listeria out have worked.
But how do you know?
This is where environmental swabbing comes in.
If you take swabs from likely places in your processing area, you get a good idea about how good the control measures really are.
You’ll need to design your own sampling plan by identifying sampling sites inside your premises.
[Image of an example sampling plan, with clearly identified sampling sites. Images of drains, wet floors, large racks and door handles.]
You should include areas that you think might become contaminated from time to time including some of those hard to clean areas.
You might have to go looking for some of those nooks and crannies that aren’t always obvious.
And if you do find Listeria, you can take some corrective action, such as extra cleaning, before it gets completely out of hand and contaminates your products.
[Close up of Geraldine.]
Let’s meet Geraldine.
Geraldine’s going to explain how you can take swab samples from the processing area for Listeria testing.
Let’s go with Geraldine and see what sampling gear we need.
[Sampling material sits prepared on table.]
We are going to start with these large gauze swabs because they seem to be best for picking up Listeria.
Here’s a swab that’s been left out so you can see what it’s like.
It's just an ordinary cotton gauze wound dressing that's been sterilised in some special liquid so it's moist and ready to use.
You need forceps to hold onto the swab.
You need a container of 70% alcohol or meths to sterilise the forceps between samples.
And you need sterile bags to put the swabs in after you have done your swabbing.
Label each bag with a vivid marker before you start.
Geraldine is writing the date and the sample location. The location has been taken from the site sampling plan.
You can add additional samples if you see anything interesting on the day.
[Geraldine displays a short flexi-swab with a blue handle, and demonstrates using the flexi-swab on a table.]
This is another type of swab used by some companies. These flexi-swabs are convenient to use, but they are not as good at picking up low numbers of Listeria from the processing environment.
You can’t apply as much pressure to the swab as you can with a large gauze swab.
[Geraldine places the sampling materials into a small blue chilly bin.]
Geraldine: I like to carry everything in a container that can be easily cleaned on the way into the processing area.
We are going to start in the processing area and work our way out from there.
That means we start in the high risk areas while we are still clean.
Otherwise we run the risk of introducing contaminants into the high risk areas from other, less clean areas.
OK, let’s get going.
Now, remember to follow all of the rules for safe entry.
[Sped up shot of Geraldine changing from coat to clean overalls, gumboots and hair net behind a red-line and spraying chilly bin with disinfectant. Geraldine moves to sink where she thoroughly washes, dries and then sanitises her hands.]
Geraldine: I’ll start with the areas that are least likely to be contaminated.
Let’s get the gear out.
[Geraldine prepares the sampling equipment, dipping forceps in alcohol and safely removing a swab.]
First you need to sterilise the forceps. Flick off the alcohol so it doesn’t interfere with the sample.
Next you need to carefully remove one swab from the pottle.
The good thing about these particular forceps is that they lock so you can’t drop things.
Unless you want to, of course.
Alternatively, you could use long stainless steel tweezers.
I am going to start by swabbing a food contact surface like this food preparation table.
[Geraldine swabs the table in a long, continuous motion, covering a large surface-area of the table. She then turns over the swab to ensure a thorough collection.]
The advantage of these large gauze swabs is that you can cover a very large area.
You can put a large amount of elbow grease in to get all those bugs off the surface.
You can turn the swab over so you can get multiple sides of the swab.
Don't forget, we do want to find the Listeria in the environment before it gets into our product.
[Geraldine tears perforated plastic top from bag, and loudly places forceps onto the metal table.]
Once you've taken your swab, you need to make sure that it's put in the sample bag aseptically.
That means without touching the swab or letting it come into contact with any other surface, including the outside of the bag.
Flatten the bag down.
And secure the bag.
The swab is now ready to go to the lab.
Narrator: If you have a very large area to swab, such as this rack, or even a large machine or bench, you could consider taking a number of swabs from the area and putting them all together in one sample bag, just like Geraldine is doing here.
We call this composite swabbing.
Each composite is tested as one sample, and so you can keep costs down, while significantly increasing the sensitivity of the test.
[Geraldine takes swabs of a large, multi-level steel rack, placing all swabs into one bag. Up to ten swabs may be placed in to one sample bag.]
If you composite swabs from different areas, and then get a positive result, you won't be able to tell which of the areas swabbed was positive. Only that one or more of the sites sampled was contaminated.
In this case, you'll need to resample, and retest each area again separately, to confirm the source of contamination.
Once you have sampled product contact surfaces you can move on to other parts of the processing area.
Include places likely to be touched frequently, such as door handles and taps.
Include floors, especially wet areas...
cracks or holes...
…and even drains.
These are areas that may be expected to be contaminated from time to time.
Back in the butchery we are going to look at how the flexi-swab is used.
[Geraldine labels swab tube with ID number, date, sample location and sample number with a permanent marker.]
Remember to label the swab tube before sampling.
Include your ID, sample date and sample number or description.
Be careful to only touch the handle during swabbing.
Swab as large an area as you need.
Press as firmly as you can to improve the chances of picking up Listeria from the surfaces being swabbed.
When you have finished replace the swab into the tube.
[Image of multiple swab samples, both gauze and flexi-swab, in chilly bin. Geraldine transfers samples from chilly-bin to small plastic container. She then places the container into the fridge.]
Here are the swab samples ready to be packed up for the courier.
It’s best to keep them in the fridge until you are ready to pack them up.
You will need to fill in a sample submission form provided by the lab.
You need to include your contact information, name, address, email address, contact phone number etc, as well as the sample information.
You need to put the completed form into a plastic bag so it doesn’t get wet inside the chilly bin.
Ice or freezer packs will keep the samples cool during transport to the lab.
This is really important to keep any Listeria in good condition, and to stop all the other bacteria from growing and ruining the sample.
Placing a paper towel between the freezer pads and sample stops the sample from freezing.
Place all of the swab samples into another bigger plastic bag.
Add the bag with the sample submission form and close it off tightly with a knot or rubber band.
Seal the container. Attach an address label for the lab.
[Geraldine places ice-packs into polystyrene ice-box, with a paper towel, bagged refrigerated samples and bagged sample submission form. She seals the ice-box with packaging tape.]
Keep the chilly bin in the fridge or chiller if the courier pickup is going to be more than about one hour.
Arrange courier pick up to get samples to the lab within 24 hours of sampling.
And that’s it. Job done.
OK, so that’s it.
[Shot of retail butchers standing in front of camera, as if narrator is talking to them.]
The lab should have your results in a couple of days so you can keep on top of any Listeria contamination issues.
Remember, don’t be afraid of positive results.
This gives you an opportunity to sort out your systems before your products become contaminated.
[Credits roll and video ends.]
Meat processing requirements
Find out more about the requirements you need to meet if you engage in the processing of meat and game: