"Harmless” Listeria species developing pathogenic resistance
Listeria monocytogenes, is a foodborne, pathogenic bacterium, is known worldwide for its resistance to various process (temperature, pH, preservation techniques). However, a recent study in South Africa shows that two non-pathogenic species – L. innocua and L. welshimeri, develop dangerous sequences that are potentially harmful to humans.

Some strains of L. innocua and L. welshimeri show resistance to temperature, pH, dehydration and other stresses, and show the L. monocytogenes virulence sequences.

They are commonly found in the environment, including soil, water and various food sources. These species are generally considered harmless to humans and are often used as surrogates for Listeria monocytogenes’ studies in food safety research.

The study also found that some strains of Listeria have developed resistance to widely used disinfectants and the CRISPR-cas-type adaptive immune system was also found in the investigated strains. These two non-pathogenic strains of Listeria have been found in raw, dried and processed meat in commercial food processing facilities in South-Africa.

The study confirms other researches showing increasing resistance to non-pathogenic Listeria species in other parts of the world. It highlights the need for continued monitoring of Listeria species, not just Listeria monocytogenes, to ensure that food safety measures are effective in protecting human health.


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