In the food processing industry, the deadly bacteria Listeria monocytogenes is monitored closely. Not only can the bacteria make people extremely ill, it is known to be developing resistance to various food safety measures across the world.
However, two ‘harmless’ species of Listeria are also developing a surprising number of characteristics potentially harmful to humans.
A Whole Genome Sequencing study in South Africa, from a team of researchers with first author Dr Thendo Mafuna at the University of Johannesburg, shows some of the changing characteristics of Listeria found in the country.
The study shows that Listeria innocua strains are developing resistance to temperature, pH, dehydration and other stresses; as well as hypervirulence genetically identical to that of Listeria monocytogenes.
Some strains of L. innocua and L. welshimeri in the study show all three genes for resistance to a widely-used disinfectant, from the quaternary ammonium compound (QAC or QUAT) group of chemicals.
Two strains of L. innocua they analysed have developed three or more concerning pathogenic characteristics, including CRISPR CAS-type adaptive immune systems.
The two non-pathogenic strains of Listeria were sampled in raw, dried and processed meats at commercial food processing facilities in the country.
The study confirms other research showing growing resistance in non-pathogenic Listeria species in other parts of the world.