Effect of antibiotics in the first week of life on faecal microbiota development

Background: Infants are frequently exposed to antibiotics (AB) in the first week of life for suspected bacterial infections. Little is known about the effect of AB on the developing intestinal microbiota. Therefore,we studied intestinal microbiota development with and without AB exposure in the first week of life in term born infants.Methods We analysed the faecal microbiota from birth until 2.5 years of age by 16S rRNA gene ampli consequencing in a cohort with 56 term born infants,exposed to AB in the first week of life (AB+) (AB for 2–3days (AB2, n=20), AB for 7 days (AB7, n=36)), compared with 126 healthy controls (AB-). The effects of AB and duration were examined in relation to delivery and feeding mode.Results AB+ was associated with significantly increased relative abundance of Entero bacteriaceae at 3weeks and 1 year and a decrease of Bifido bacteriaceae, from 1 week until 3 months of age only in vaginally delivered, but not in C-section born infants. Similar deviations were noted in AB7, but not in AB2. AfterAB, breastfed infants had lower relative abundance of potentially pathogenic Enterobacteriaceae compared with formula fed infants and recovered 2 weeks faster towards controls.Conclusions AB exposure in the first week of life alters faecal microbiota development with deviations in the relative abundance of individual taxa until 1 year of age. These alterations can have long- term health consequences, which emphasises the need for future studies aiming at restoring intestinal microbiota after AB administration.