Listeria innocua and welshimeri species are developing harmful characteristics similar to L. monocytogenes

A study published in the ASM journal “Microbiology Spectrum” used WGS to provide insights into two species of presumed nonpathogenic Listeria innocua and L. welshimeri and found that they are developing a surprising number of characteristics that are potentially harmful to humans. The study used a comparative genome approach to analyze 41 genome sequences belonging to L. innocua and L. welshimeri isolated from food and food processing facilities. Genetic determinants responsible for disinfectant and stress tolerance were identified, including the efflux cassette bcrABC and Tn6188_qac_1 disinfectant resistance determinant and stress survival islets. These disinfectant-resistant genes were more frequently found in L. innocua (12%) than in L. welshimeri (2%). Several isolates representing the presumed nonpathogenic L. innocua still carried virulence-associated genes absent in all L. welshimeri isolates. The results suggest that the presumed nonpathogenic isolates, especially L. innocua can carry genes relevant to the strain’s virulence and stress tolerance in food processing facilities. The presence of genetic loci previously associated with adaption/survival in stressful conditions was higher in L. innocua, especially L. innocua ST132, than in any of the L. welshimeri strains. Some strains of L. innocua and L. welshimeri examined in the study show three genes for resistance to a widely-used disinfectant from the quaternary ammonium compounds. The study highlights that the low occurrence of important core genes could result from a functional CRISPR-cas system in the Listeria genomes. @ https://journals.asm.org/doi/10.1128/spectrum.01189-22