Phenotypic and genotypic characterization of Listeria monocytogenes in clinical ruminant cases in Korea

Listeria monocytogenes is a foodborne human and veterinary pathogen. This study aimed to determine the phenotypic and genotypic characteristics of L. monocytogenes isolates from clinical cases of Korean ruminants. We collected 24 L. monocytogenes isolates from clinical cases with caprine neurological symptoms and bovine abortion. The most prevalent serotypes were 4b (IVb), 1/2a (IIa; IIc), and 1/2b (IIb). All isolates, including two found in humans, formed three genetically diverse pulsed-field gel electrophoresis clusters according to serotype, lineage, and sequence type. The most prevalent sequence type was ST1, followed by ST365 and ST91. L. monocytogenes isolates from ruminant listeriosis were resistant to oxacillin and ceftriaxone. These clinical ruminant isolates showed diverse lineage, serotype (serogroup), and sequence type characteristics. Considering that the atypical sequence types exhibited clinical manifestations and histopathological lesions, further study is needed to elucidate the pathogenicity of genetically diverse ruminant L. monocytogenes isolates. Furthermore, continuous monitoring of antimicrobial resistance is required to prevent the emergence of L. monocytogenes strains resistant to common antimicrobials.