Recently published findings by Austrian researchers at the University of Veterinary Medicine in Vienna provide strong evidence that a genetic mechanism allows Listeria monocytogenes to develop resistance to a sanitising chemical often used in the food processing industry to control bacterial contamination.
It is known that certain strains of Listeria are resistant to the quaternary ammonium compounds (QACs) often used to sanitise food processing equipment and food preparation areas, but the resistance mechanism is unknown. The researchers used next-generation sequencing techniques to examine the genomes of two L. monocytogenes strains known to be resistant to the widely used QAC disinfectant benzalkonium chloride. They identified a novel transposon called Tn6188, which is related to transposons found in species such as Staphylococccus aureus and could have been acquired from other bacteria.
Screening of a further 91 strains of Listeria showed that Tn6188 was present in 10 isolates from food and food processing environments, all of which were more resistant to benzalkonium chloride that strains lacking the transposon. Tn6188 includes a gene that encodes a protein called QacH, which is associated with disinfectant resistance. Tests with mutants in which that gene had been deleted showed reduced resistance to benzalkonium chloride. The researchers conclude that this suggests that Tn6188 is responsible for benzalkonium chloride tolerance in certain L. monocytogenes strains.
The findings are published in the journal PLOS One and can be found in full here.