What is Listeria and how can it affect us?

Recent events in the Estonian fish Industry have brought up a concern regarding Listeria and its influence on health.
Listeria is a stick -shaped bacteria with 20 different species. One of which, Listeria monocytogenes, can be harmful to humans. The bacteria got its name from Joseph Lister, who discovered that sterilization of scalpels reduce the risk of future infections.
Listeria monocytogenes is widely spread bacteria - from soil to water and intestine. Listeria is also found in fresh fish, but is important to understand that a small amount of bacteria is not harmful for people outside the risk group. Moreover, after cooking the fish, it is totally harmful, due to the fact that Listeria is being destroyed at the temperature 65°C.

Fish is an important foodstuff. The problems with Listeria are associated with specific fish products that have a long shelf life and are cold smoked or lightly salted fish products. Manufacturers want long shelf time and consumers´ food with fewer preservatives. Therefore, manufacturers have found the golden mean and with little preservatives achieve long shelf time. Unfortunately, the Listeria bacteria can multiply in long shelf time hundreds of times, even at lower temperatures. This is the reason why we can detect Listeria during the packaging, but cannot predict its time at the end of the self time.

Fish is not the most harmful food with regard to Listeria. In fact, it is found in several other products. For example, in 1990, there were Listeria outbreaks in salami and hot dog sausages. Most of the outbreaks are caused by milk and dairy products. Infections can also be caused by unwashed or spoiled vegetables.

Food poisoning is caused by different bacteria. The most dangerous are Campylobacter, Clostridium perfringens, Escherichia coli, Listeria and Salmonella. From the recent problems in the Estonian fish industry, there is a lot to learn - if the bacteria are found, measures should be taken in order to control the situation. We can see, that collaboration between medical authorities and food safety is important in critical situation. We need to think how we can make the Estonian system better and more effective. In similar situations, we should establish a standard procedural rule.

Tanel Tenson, Professor of Technology of Antimicrobial Compounds