The role of Klebsiella populations in preterm infants.

The preterm infant microbiota is dominated by Enterobacteriaceae (Escherichia, Klebsiella or Enterobacter spp.), Enterococcus and Staphylococcus spp. Recent work has demonstrated the development of this microbiota is predictable and driven by simple microbe-microbe interactions. Because of their systemic immaturity, including an underdeveloped immune system, preterm infants are susceptible to a range of infections. Numerous retrospective studies have examined the association of the preterm gut microbiota with diseases such as necrotizing enterocolitis (NEC), early-onset sepsis and late-onset sepsis. To date, no single bacterium has been associated with infection in these infants, but a Klebsiella/Enterococcus-dominated faecal microbiota is associated with an increased risk of developing NEC. Staphylococci aid and enterococci inhibit establishment/maintenance of gastrointestinal Klebsiella populations in preterm infants, though the mechanisms underlying these interactions are poorly understood. Klebsiella spp. recovered from healthy and sick preterm infants display similar antimicrobial resistance and virulence profiles, giving no clues as to why some infants develop potentially life-threatening diseases while others do not. The identification of cytotoxin-producing Klebsiella oxytoca sensu lato in the gut microbiota of some preterm infants has led to the suggestion that these bacteria may contribute to NEC in a subset of neonates. This mini review highlights current knowledge on Klebsiella spp. contributing to the preterm gut microbiota and provides insights into areas of research that warrant further attention.