Hypervirulent Listeria isolated from a wild rabbit in Canada

Listeria monocytogenes is the causative agent of listeriosis, a major foodborne disease with a 30% mortality rate in humans. Although L. monocytogenes can infect animals, whether wildlife can serve as a reservoir remains understudied, especially in Canada. Here, we characterized an L. monocytogenes strain (W0463-24) extracted from a wild cottontail rabbit (Sylvilagus floridanus) submitted to the Canadian Wildlife Health Cooperative at the University of Guelph. The rabbit had severe swelling of the head, multiple scabs around the muzzle and eyes, and was diagnosed with disseminated lymphoma, multifocal necrotizing hepatitis with gram-positive bacteria, and nematodosis. Liver and spleen were PCR-negative for Francisella tularensis, and liver was 4+ for L. monocytogenes on bacterial culture. Whole-genome analysis characterized isolate W0463-24 as sequence type 1 (ST1), clonal complex 1 (CC1), and lineage I. Multiple virulence and stress response genes were identified in silico, including the Listeria pathogenicity island 3 (LIPI-3). Invasion of human colon adenocarcinoma (Caco-2) cells in vitro was significantly greater with W0463-24 compared with wild-type strain 10403S. We found that this ST1, CC1, lineage I wildlife isolate has high pathogenic potential, emphasizing wildlife both as potential reservoirs and as populations vulnerable to L. monocytogenes infection.