Phenotypic and Genomic Assessment of Listeria monocytogenes Virulence
Cardenas Alvarez, Maria Ximena
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Listeria monocytogenes is the etiological agent of listeriosis in humans and ruminants causing bacteremia, central nervous system (CNS) infections, abortion, and gastroenteritis among other clinical outcomes. Recent studies have integrated whole genome sequence (WGS), epidemiology data, and host susceptibility to provide evidence for variation in virulence among strains, as a small number of hypervirulent clones have been found linked to a high proportion of human and ruminant invasive listeriosis cases, however, still little is known about variation in virulence across different L. monocytogenes subgroups. To assess and compare the genetic diversity of clinical listeriosis isolates from ruminants in the Upper Great Plains states, we used multilocus sequence typing (MLST) and found that the variation in virulence potential varies among clonal complex (CC), which is reflected in the epidemiology of L. monocytogenes. Based on these results, we evaluated the strains’ virulence potential in Galleria mellonella through larvae survival, LD50, and cytotoxicity, and monitored health index scores and bacterial concentrations post-infection as quantifiable indicators of virulence and immunogenicity. Our findings suggest that strains belonging to CC14, as well as isolates from MN infections are hypervirulent in G. mellonella, as they need a lower bacterial concentration to cause disease and produce a low-level infection that could help in evading the host immune response. We also identify genomic elements associated with strains causing three different clinical outcomes: bacteremia, central nervous system infections, and maternal-neonatal infections. By analyzing 232 whole genome sequences from invasive listeriosis cases, we identified orthologous genes of phage phiX174, transfer RNAs and type I restrictionmodification (RM) system genes along with SNPs in loci associated with environmental adaptation such as rpoB and the phosphotransferase system (PTS) associated with one or more clinical outcomes. Novel genetic variants may be associated with a particular virulence phenotype, as it is likely that strains causing the same clinical outcome share unique genetic elements. Variation in virulence among L. monocytogenes subgroups may confer an increased ability to cross host barriers or higher adaptability to food processing environments, thus the investigation of strainspecific genetic features can impact the design of prevention and management plans for listeriosis.