LISTERIA AND BIOFILM IN FOOD INDUSTRY: HOW TO PREVENT THEM?
Listeriosis is an infection caused by the bacterium Listeria monocytogenes, a microorganism with a natural habitat in soils, plants and water. If ingested in large quantities through contaminated food, this bacterium can give very serious consequences on humans.
It is therefore essential to prevent the contamination of food surfaces by using specific cleaners and by following accurate sanitation procedures that can be easily adopted by any food and beverage producer.
THE UPGROWING RESTRICTIONS ON THIS ISSUE WORLDWIDE
Although the number of cases of listeriosis reported worldwide is relatively small to date (about 2,500 cases in Europe in 2018), there is evidence of a high rate of hospitalizations and deaths caused by this infection.
This pathogen is particularly dangerous if ingested by people with weak immune defenses; a fact that is worrying if we consider the constant rise in average age in developed countries.
For this reason national legislations have set limits to the quantity of Listeria monocytogenes present in food and beverages exitng any production plants. In some countries, such as the United States of America, there is zero tolerance for the presence of this microorganism. Of course, the limits imposed in the United States are also valid for producers of other countries who want to export in this country, and therefore the organizations which authorize these movements of goods put a lot of pressure in order to have food totally free from Listeria.
HOW LISTERIA CONTAMINATION OCCUR
As it lives on the soil and in surface waters, it is with raw materials that Listeria enters food industries. It is a microorganism that does not have great resistance to heat treatments or other antimicrobial treatments; however, it tolerates high saline levels and is able of multiplying even at low temperatures.
Moreover, in the last years, it has been proven that Listeria is not only capable of living inside biofilms formed by other microorganisms, but it is itself a biofilm promoter.
Protected by biofilm, it becomes less sensitive to disinfection treatments and multiplies undisturbed continuously to contaminating food and beverages with which it comes in contact.
Until recently, it was thought that contamination occurred only from "mature" biofilms, i.e. biofilms big enough to be "damaged" by external flows, or from which microorganisms move away because they can no longer sustain inside.
Recent papers have however shown a dynamic relation between biofilm and external environment, which represent a continuous threat for food contamination: this has changed the approach to prevent Listeria contamination, and more generally by any biofilm, which until now was mainly oriented to prevent biofilm growth, using enzymatic preparations to limit its size.
THE PREVENTION IN FOOD INDUSTRY
The relevance of acting on the first phase of biofilm development, i.e. the initial phase of adhesion of promoter microorganisms to surfaces, has determined important innovations in the prevention of food-related contamination.
Today we know that adhesion is favored by the presence of organic and inorganic residues: in particular, the presence of calcium ions is fundamental for the microbial structures involved in anchoring to the surfaces.
To summarize, it is important to consider these factors when setting sanitation procedures to be adopted in the production plants:
- The microorganisms can anchor and protect themselves only if traces of organic matter and mineral deposits are present;
- Only suitable sequestrant and surfactant-activated cleaning solutions avoid the deposits (mentioned above) and thus prevent the first phase of biofilm formation;
- These concepts are based thermodynamics laws;
- Washes carried out with simply caustic solutions (e.g. only soda) do not have the ability to remove inorganic residues from surfaces.