The abundant skin commensal, Staphylococcus epidermidis, is the leading cause of late-onset sepsis (LOS) in preterm infants but rarely causes infections in term infants and adults. Staphylococcal virulence mechanisms and the role of the preterm immune responses in driving these life-threatening infections remain poorly understood. Using an ex vivo sepsis model, we challenged whole blood from preterm infants (30-32 weeks GA; n=8), term infants (>37 weeks GA; n=8), and adults (18-25 years; n=8) with either live S. epidermidis or S. aureus (~107 colony-forming units, CFU/ml) for 90 minutes. Dual RNA-sequencing (RNA-seq) was performed using a newly optimised, in-house methodology to simultaneously assess host and pathogen gene expression, identifying common and pathogen-specific responses across cohorts.
We found shared immune processes induced in all age groups upon bacterial challenge, including cytokine (IL1A, IL1B, IL6, IFNB1) and chemokine (CCL20, CCL3, CCL7, CXCL2) signalling. Preterm infants also exhibited unique responses, such as , Wnt signalling, and hypoxia pathways in response to S. epidermidis. Our findings moreover indicate that bacterial gene co-expression, including iron acquisition and heme biosynthesis genes, are influenced by host developmental age, highlighting the complexity of host-bacterial interactions in the early stages of neonatal sepsis.