The aim of this study is to evaluate the potential role of the enteral feeding systems on the bacterial colonization of premature infants during their NICU admittance and its evolution after 2 years, which is the age when the infant's gut starts to contain an adult-like microbiota.

First spontaneously evacuated meconium and fecal samples were collected by the medical staff of the Hospital weekly from the diapers of the infants during their stay at the Neonatal Intensive Care Unit.

To evaluate the potential role of the enteral feeding systems as a site for colonization by nosocomial bacteria, and, its impact on early gut colonization of preterm neonates, mother's own milk, donor milk and preterm formula samples were obtained after passing through the external part of the enteral feeding tubes and cultured.

Later, when the infants reached 2 years of age, parents were contacted by phone to provide an additional fecal sample if their infants had not taken antibiotics within the previous 2 months.

Inclusion Criteria:

• gestational age of less than 32 weeks or with birth weight of less than 1,200 g

Exclusion Criteria:

• any malformation or suffering from any genetic metabolic disorder

Preterm infants born from October 2009 to June 2010 at the Hospital 12 de Octubre with a gestational age of less than 32 weeks or with birth weight of less than 1,200 g