Novel, highly divergent clones in Listeria monocytogenes serotype 4b in North America: Sublineages 782 and 1039, members of the hypervirulent clonal complex 2

Sublineages 782 and 1039 of Listeria monocytogenes serotype 4b are newly recognized CC2 lineages, found only in North America, and are strikingly divergent from SL2.

• Why it matters: Serotype 4b drives most human listeriosis, yet CC2 diversity beyond the dominant SL2 is poorly characterized, limiting understanding of how additional lineages persist and reach people.
• What they did: The study used phylogenetic analysis and comparative genomics, linking human listeriosis isolates with North American surface water and wildlife strains showing up to 7 core genome allelic mismatches.
• The result: SL782 and SL1039 show shared phage-resistance patterns and lineage-specific traits (SL782 lacks a conserved serotype 4b gene; SL1039 carries LIPI-3 and is almost always tetracycline-resistant via Tn916.1039), suggesting ecosystem adaptations may have enabled their emergence.

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