Tracing <i>Staphylococcus capitis</i> and <i>Staphylococcus epidermidis</i> strains causing septicemia in extremely preterm infants to the skin, mouth, and gut microbiota

Septicemia is a major cause of morbidity in preterm infants. Coagulase-negative staphylococci (CoNS) can colonize skin, oral cavity, and intestines and are a common cause of septicemia in this group. The relation between CoNS colonization pattern at the species and strain level and septicemia has scarcely been studied. We mapped colonization of the skin, oral cavity, and intestines by CoNS species in extremely preterm infants and speciated and strain-typed the skin, mucosal, and blood isolates. Two-thirds of the CoNS septicemia blood strains, including a majority of <i>S. capitis</i> strains belonging to the NRCS-A clone, were tracked to the commensal microbiota. We demonstrated that CoNS species differ in their colonization patterns, whereby <i>S. capitis</i> was primarily a skin colonizer. However, its colonization of the oral cavity was enhanced among infants developing septicemia. Our study provides a starting point for further explorations of the relationship between CoNS colonization and septicemia in preterm infants.