Group B Streptococcus Drives Major Transcriptomic Changes in the Colonic Epithelium.

Group B Streptococcus (GBS) is a leading cause of infant sepsis worldwide. Colonization of the gastrointestinal tract is a critical precursor to late-onset disease in exposed newborns. Neonatal susceptibility to GBS intestinal translocation stems from intestinal immaturity; however, the mechanisms by which GBS exploits the immature host remain unclear. β-hemolysin/cytolysin (βH/C) is a highly conserved toxin produced by GBS capable of disrupting epithelial barriers. However, its role in the pathogenesis of late-onset GBS disease is unknown. Our aim was to determine the contribution of βH/C to intestinal colonization and translocation to extraintestinal tissues. Using our established mouse model of late-onset GBS disease, we exposed animals to GBS COH-1 (WT), a βH/C-deficient mutant (KO), or vehicle control (phosphate-buffered saline [PBS]) via gavage. Blood, spleen, brain, and intestines were harvested 4 days post-exposure for determination of bacterial burden and isolation of intestinal epithelial cells. RNA sequencing was used to examine the transcriptomes of host cells followed by gene ontology enrichment and KEGG pathway analysis. A separate cohort of animals was followed longitudinally to compare colonization kinetics and mortality between WT and KO groups. We demonstrate that dissemination to extraintestinal tissues occurred only in the WT exposed animals. We observed major transcriptomic changes in the colons of colonized animals, but not in the small intestines. We noted differential expression of genes that indicated the role of βH/C in altering epithelial barrier structure and immune response signaling. Overall, our results demonstrate an important role of βH/C in the pathogenesis of late-onset GBS disease.