FIGHTING LISTERIA MONOCYTOGENES BY STUDYING ITS HIGH ADAPTABILITY

Listeria monocytogenes , one of the most dangerous foodborne pathogenic microorganisms, is a very resistant bacterium, able to survive, and even reproduce, in particularly harsh environmental conditions, from temperature to salt, from acidity to low water activity. Thanks to these characteristics, not only is Listeria widely spread in the environment, but it can contaminate food processing plants, where its elimination can be particularly difficult.

Adaptability is the key: in front of environmental stress, the bacterium activates specific parts of its genome, leading to the synthesis of proteins that enable it to cope with adverse situations. Understanding how Listeria adapts to the environment is the aim of a novel research carried out by the National Reference Laboratory for Listeria monocytogenes of the Istituto Zooprofilattico Sperimentale (IZSAM), Teramo, Italy, published in the journal Proteomics.

The study examined a particular strain of Listeria, named ST7, which in the past years caused a series of listeriosis outbreaks in central Italy, with a number of very serious cases. Researchers exposed the bacteria to moderately stressful environmental conditions by varying temperature, acidity level and salt concentration. "The conditions we choose - says Federica D'Onofrio, PhD student at the Faculty of Bioscience and Technology for Food, Agriculture and Environment of the University of Teramo, first author of the paper - are the same occurring in various stages of food production, distribution and sale. In other words, very close to what we can find in shops or supermarkets”.

For each different situation, researchers analyzed the bacteria using immunoproteomics and bioinformatics techniques, identifying which genes were activated in response to stress. "We saw - continues D'Onofrio - that, compared to bacteria grown in optimal conditions, those subjected to stress produced specific proteins, some of which currently have no known function. The biological mechanisms involved in this response are: cell motility, carbohydrate metabolism, oxidative stress and DNA repair”.

As with any living organism, Listeria adapts in order to survive. Only that it manages to do it very efficiently. "The production of proteins determined by the activation of specific genes under stressful conditions - says Mirella Luciani, IZSAM Immunology and Serology Department, PhD tutor of Federica D'Onofrio - is a fundamental element of the ability of these bacteria to spread in the environment and, in some cases, to persist even in food production plants. Considering how dangerous listeriosis can be for some particularly vulnerable categories, such as children, elderly, immunosuppressed people and pregnant women, investigating the defense mechanisms of Listeria will help us to find new strategies to fight the bacteria".