Differential virulence gene carriage in Listeria monocytogenes strains from neonatal sepsis: insights from whole-genome sequencing of a multicenter cohort

Background Neonatal Listeria monocytogenes ( L. monocytogenes ) sepsis is rare but clinically severe. Existing research primarily focused on epidemiology, clinical characteristics, and prognosis, whereas WGS-based descriptions of virulence gene repertoires in neonatal isolates remain limited. Methods This multicenter retrospective case series analyzed 11 neonates diagnosed with culture-confirmed L. monocytogenes sepsis. Perinatal data, clinical presentations, interventions, complications, and outcomes were recorded. Whole-genome sequencing (WGS) was performed on four available L. monocytogenes isolates, with virulence gene profiles annotated against public databases. We summarized the carriage of selected virulence genes, including inlP, actA, auto, vip, and bsh , and interpreted these profiles together with case-level clinical severity and phylogenetic background. Results All cases were early onset, predominantly affecting preterm infants, requiring respiratory support, and with a high incidence of severe complications. All four sequenced isolates harbored core virulence genes associated with adhesion, invasion, motility, and stress survival. The nSOFA scores for Cases 1–4 were 4, 7, 2, and 2, respectively. Case-level differences were observed in the carriage of virulence genes, including actA , auto , vip, etc. Core-genome SNP phylogenetic analysis revealed that the four isolates belonged to different clonal complexes, with Cases 1 and 2 belonging to the CC1/lineage I, and Cases 3 and 4 belonging to the lineage II-related clonal complex, including CC155 and CC121. Expanded analysis incorporating 39 public reference genomes suggested that the selected accessory virulence genes, particularly actA and bsh carriage, should be interpreted within the MLST lineage background rather than as direct indicators of clinical severity. Conclusion This multicenter study provides preliminary clinical and genomic data on neonatal L. monocytogenes sepsis. The observed heterogeneity in virulence gene profiles indicates genomic diversity among isolates and should be interpreted within a phylogenetic context. Larger-scale, lineage-matched cohort studies and functional investigations are needed before any genotype–phenotype relationships can be inferred.