Effect of Intrapartum Antibiotic Prophylaxis (IAP) on the Development of Neonatal Gut Microbiota

At birth, the neonatal gastro-intestinal (GI) tract is rapidly colonized by maternal and environmental bacteria; the first colonizers are generally aerobes and facultative anaerobes, followed by strict anaerobes (e.g. Bifidobacterium spp., Bacteroides spp., and Clostridium spp.). The composition of gut microbiota is influenced by several factors, such as mode of delivery, gestational age, maternal intestinal and vaginal microbiota, type of feeding, hospitalization after birth and use of antibiotics and probiotics.

Gut microbiota of term infants, vaginally delivered and exclusively breastfed, is considered to be ideally healthy, with a low count of C. difficile and E. coli and a high number of Bidifobacteria and Lactobacilli, which positively influence the host's health by activating immunocompetent cells in the GI tract, promoting the production of secretory IgA and increasing the bactericidal activity of neutrophils and cell-mediated immunity such as NK cell activity.

Group B Streptococcus (GBS) is one of the most important causes of neonatal infections and sepsis. Infants vaginally delivered may acquire GBS during the birth process from maternal vagina, cervix or rectum, where it resides in approximately 10-20% of pregnant women. Since the mid-90s, the incidence of early-onset GBS sepsis is significantly reduced, due to the introduction of GBS universal screening during late pregnancy and consequent intrapartum antibiotic prophylaxis (IAP) in GBS-positive women.

Recent data suggest that the use of antibiotics in early life could alter the commensal gut microbiota, thereby impairing the balance between health and disease later in life. The effect of IAP on bacterial colonization of the infant's gut has not been largely investigated. Moreover, currently available data on this issue largely derive from studies performed using culture-based techniques; however, accurate culture-based results are influenced by the selection of the correct media, temperature, oxygen content and time for growth, and for this reason as little as 10-50% of the entire gut bacteria are easily cultured. Molecular techniques, based on the amplification of the 16S ribosomal bacterial RNA gene to differentiate prokaryotic taxa, have been recently developed for the study of gut microbiota, thus enabling a more detailed characterization of bacterial communities than standard culture.

We have previously evaluated the effect of IAP in a relatively small sample of exclusively breast-fed term infants vaginally delivered by means of molecular techniques; at 7 days of life there were several differences in microbiota composition between infants IAP-exposed and not exposed.