SOUTH AFRICA – A study conducted in South Africa and recently published in the journal Microbiology Spectrum has concluded that Listeria innocua strains are developing resistance to temperature, pH, dehydration, and other stresses. 

Listeria monocytogenes is extensively monitored in the food processing business since it can be fatal to people.

The infection not only has the potential to make people very ill, but it is also now known to be building resistance to many food safety measures globally.

The study used whole-genome sequencing to provide insights into two species of presumed nonpathogenic Listeria—L. innocua and L. welshimeri.

Some of the L. innocua and L. welshimeri strains tested for the study exhibited three genes for resistance to a common disinfectant from the class of chemicals known as quaternary ammonium compounds (QAC or QUAT).

The study included 258 isolates from butcheries, abbatoirs, retail establishments, cold storage facilities, and processing facilities located throughout South Africa.

Of these, three isolates of nonpathogenic L. welshimeri and 38 isolates of nonpathogenic L. innocua were identified.

Additionally, two of the L. innocua strains examined in the study had three or more pathogenic traits that were alarming, including CRISPR CAS-type adaptive immune systems.

“The Listeria innocua that we tested has some of the genes that are also found in pathogenic Listeria monocytogenes.

“These shared genes between L. innocua and L. monocytogenes are also responsible for disease in humans and stress tolerance such as resistance to the disinfectant Benzalkonium chloride,” said Thendo Mafuna, Ph.D., a Lecturer at the University of Johannesburg, and co-author of the study.

Each of the L. innocua strains examined in the study also exhibited the entire sequence of the LIPI-4 hypervirulence gene, which can harm humans.

Dr. Mafuna claims that the study supports other global studies showing an increase in nonpathogenic Listeria species resistance.

For instance, according to him, the LIPI-4 sequence is the same as the pathogenic L. monocytogenes sequence identified by the Pasteur Institute in Paris.

The Lecturer says that because these novel Listeria strains are developing resistance to disinfectants, food processors should be on the lookout for them.

“Big industrial food processors may want to investigate how efficient BC or quat disinfectants are in their facilities. This can be done by taking swabs before cleaning and again after cleaning [and] culturing those to see how well the disinfectant regimens are working,” Dr. Mafuna says.

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