Common Questions About Listeria, Answered

With Listeria back in the news this week we wanted to explain in more detail what Listeria is, who it affects and how we could reduce the risk of it. Food manufacturers across the country regularly check production environments for the bacterium so they can protect consumers from harm.

Here are the most common questions people ask about Listeria:

What is Listeria?

The full term for Listeria is Listeria monocytogenes. Listeria is a bacterium that causes an illness called listeriosis. It is very rare to see illnesses from listeria. In most people, it can cause mild symptoms e.g. fever, vomiting and diarrhoea. However, it can cause serious symptoms and even death for certain groups of vulnerable people.

Who is at risk?

The people more at risk of getting ill from Listeria are:

  • Elderly people
  • Newborn babies
  • Pregnant women and their unborn babies
  • People with weakened immune systems, such as those suffering from cancer

How does it spread?

Listeria can be found in different types of food. It is more common in refrigerated ready-to-eat foods that do not need further cooking. Further cooking would act as extra protection to destroy the bacteria. Mostly found in the following foods:

  • Cooked sliced meats
  • Pate
  • Prepared sandwiches & salads
  • Cured meats & smoked fish
  • Cooked shellfish
  • Mould-ripened soft cheeses e.g. Brie and Camembert

How do I reduce the risk at home? 

Luckily there are several things you can do to reduce the risk when preparing food at home:

  • Keep chilled ready-to-eat foods cold
  • Make sure your fridge is working properly and set to 5⁰C or below
  • Don’t eat food past their use-by date
  • Follow the storage instructions on the food label
  • Use opened refrigerated food within two days (unless instructions on the packaging say otherwise)
  • Cook or reheat foods until they are piping hot all the way through
  • Keep ready-to-use and raw foods separate
  • Always wash fruit and vegetables thoroughly especially if eating them raw

How do I protect my consumers? 

Special attention is needed when cleaning and sanitising in food processing areas, particularly on conveyor belts and equipment. Continuous sampling of these food plant environments for Listeria is extremely necessary. This gives facilities an early warning that there might be a problem. The following products are recommended for use across the food industry:

Hygiena™ InSite™ Listeria Rapid Environmental Test 

These tests contain a chromogenic liquid media formulated with antibiotics, growth enhancers, and colour-changing compounds specific to the Listeria species. To use, simply swab the test area and incubate for 24-48 hours in a digital dry block incubator.


  • Delivers results in 24-48 hours
  • Easy-to-use – ‘snap & squeeze’ Snap-Valve™ technology
  • Maximum sample pickup – large 2.5-inch foam swab
  • Write-on swab label for easy sample identification
  • Cost-effective test
  • Self-contained reagent- no transfers minimizing the chance of contamination
  • Colour-changing device is easy to interpret

3M™ Petrifilm™ Environmental Listeria (EL) Plates

These Petrifilm plates are a sample-ready culture medium containing selective agents, nutrients, a cold-water-soluble gelling agent and a chromogenic indicator. This is designed to analyse environmental samples and help increase the efficiency of monitoring plant sanitation.


  • Rapid results in 27-31 hours from sample collection
  • Proven cost-effective tool for the detection
  • Quantitative results allow identification of hot spots in plant and track progress over time
  • Safer method: no enrichment, no culture transfers
  • Counting grid helps improve the accuracy of estimated counts
  • Chromogenic indicators provide clear differentiation of colonies

Our team are on hand to help find the right solutions for your production problems, from rapid tests and disposable consumables through to specialist analysis equipment and instruments.

Speak to one of our specialists today by calling 01924 444 577, emailing or hit the ‘Chat Now’ button to start a live chat with us!

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