Objective Evaluating the effects that the antibiotic, administered in the first two weeks of life, over the newborn’s composition of the intestinal microbiota and its influence on other ages of the infant.

Design Study of the prospective cohorts carried outbetween January 2013–February 2014 in the Neonatal Unit of a third levelhospital. 3 stool samples are collected: M1 (admission), M2 (discharge), M3 (1st month of life). It isanalysed the influence of the antibiotic parenteral treatment in the first 15days of life on the intestinal colonisation of the 4 bacterial groups: Bacteroids, Clostridium, Lactobacillus and Escherichia Coli, using molecular biology techniques (qPCR).

Results 27 neonates have been enrolled in the studio:15 babies have received parenteral antibiotic and 12 babies have not. The content of Lactobacillus when discharge is lower in those who have received antibiotic treatment (9,28 × 10²CFU/g vs 7,21 × 10³ CFU/g; p 0,005). This difference is the same in a month (1,79 × 10² CFU/g vs 4,77 × 10⁵ CFU/g; p 0,16). The influence of the antibiotic treatment over the colonisation of the rest of groups studied has not been demonstrated.

Conclusions The use of antibiotic in the neonatal period has shown tohave an influence on the neonate’s intestinal colonisation process, producing a decrease in the content of lactobacillus (bacterial group related to beneficial effects for the guest). This research is considered to be the basis of future strategies in order to care these neonates (specially based on probiotics).