Listeria monocytogenes is a bacterium which can give rise to food poisoning and so is a serious food safety concern in food production.
In 2015 according to Public Health England, there were 169 cases of listeriosis in England and Wales. This might not sound many, but the mortality rate for this pathogen is high at approximately 30% of cases.
The elderly and unborn / newly-born babies are most vulnerable to the disease. Listeria monocytogenes is the only member of the genus Listeria which is recognised as a human food pathogen. However, all Listeria species have the same growth requirements, and so the presence of a ‘non-hazardous’ Listeria can be indicative of the presence of Listeria monocytogenes.
Listeria is found in the general environment and so can be associated with any food that is grown in association with the soil (e.g. salad leaves). This bacterium can:
- Grow - albeit slowly - at chill temperatures and is especially a concern for chilled ready-to-eat (RTE) foods.
- Inhabit and persist in the food production environment. It thrives in conditions where there is plenty of water
- Produce protective mechanisms (for example ‘biofilms’) to help it survive.
These characteristics enable Listeria and Listeria monocytogenes to cross-contaminate foods that have undergone a process to eradicate vegetative pathogens (e.g. cooking), and so it can pose challenges to food manufacturers.
Where to look for Listeria
When monitoring for the presence of Listeria in a food production facility there are key areas to look at. Two of the most frequently contaminated are:
- Drains are the prime place to look for this bacterium, because each time the production area is cleaned, residue leaves via the drains.
- A close second on the list of places to look is ‘cleaning equipment’ such as brushes and squeegees, which are used as part of any clean-down process. Most, if not all, cleaning equipment will be used as part of routine cleaning.