Effect of Probiotics on Infant's Fecal Microbiota Composition

Inclusion Criteria: * Healthy infants * Age between 1 and 90 days * Gestational age between 37 and 42 weeks * Appropiate birth weight for gestational age (between P10 and P90) * APGAR test score for birth normal at 1' and 5' of 7-10 * Whose parents accept the follow-up of the study procedures and sign the informed consent Exclusion Criteria: * Infants participating in other clinical study * Fed with infant formula containing probiotics or other aliments or food supplement based in probiotics 4 weeks prior the start of the study * Infants who have taken antibiotics 4 weeks prior the start study * Infants with cow's milk protein allergy, lactose intolerance or other digestive diseases * Mother's pathological background and during gestation: neurologic disorders, matabolopaties, diabetes mellitus type 1, chronic disease (hypothyroidism), maternal malnutrition * Acute congenital or acquired diseases which can interfere with the growth and the normal feeding of the infant * TORCH complex infections * Every other diseases related with the immune system * Parents who can not accomplish the follow-up of the study (medical criterium)