Genomic and pathogenic characterization of Listeria ivanovii subsp. londoniensis from ovine farms in China.

BACKGROUND

Listeria ivanovii (Liv) is an anaerobic intracellular pathogen primarily responsible for listeriosis in ruminants, presenting with clinical manifestations such as gastroenteritis, bacteremia and abortion. Liv contains two validated subspecies: Listeria ivanovii subsp. ivanovii (Liv-I) and Listeria ivanovii subsp. londoniensis (Liv-L). Hitherto, the genomics and pathogenic features of Liv-L remain poorly understood.

RESULTS

Here, we characterized the genomic diversity and pathogenic traits of 10 Liv isolates from five ovine farms in eastern China with a high prevalence of listeriosis. Whole-genome sequencing (WGS) confirmed all 10 isolates belonged to Liv-L (lineage Ⅱ), bayesian time-scaled phylogenetic reconstruction placed these isolates within a monophyletic cluster of China-associated Clade I, indicating potential localized evolution. Based on an estimated mutation rate of 1.28 × 10⁻⁷ substitutions/site/year, SNP divergence (53 ~ 355 bp) suggests that these isolates approximately shared a common ancestor within the past decades to hundred years. The representative strain XYSL harboring intact pathogenic islands 1 and 2 and was assessed for its invasive capacity and humoral immune responses. Indirect ELISA demonstrated robust antibody production against two key virulence factors: listeriolysin O (LLO) and sphingomyelinase C (SmcL). Animal challenge experiments revealed that XYSL could effectively colonize in the ileum upon intragastric inoculation, and subsequently disseminate to distal organs via intraperitoneal infection.

CONCLUSIONS

These findings demonstrate that the clonally related Liv-L strains circulating in goat farms represent both a transmission risk and confirmed pathogenic threat, underscoring the need for ongoing surveillance to control of potential zoonotic and epizootic outbreaks.