Influence of intrapartum antibiotic prophylaxis against group B Streptococcus on the early newborn gut composition

Introduction: The infant gut microbiota composition is established in a relatively short time during the first two years of life. In particular birth represents a sensitive checkpoint to the future microbiota development which will exert a strong influence on human health. Several factors are known to influence the early microbial colonization of the gut in newborns as the mode of delivery, maternal microbiota of intestine, vagina and epidermis, type of infant feeding, gestational age at birth, hospitalization after birth and the use of antibiotics during the first few months of life. Conversely, the use of antibiotics on the mother during labour, referred to as intrapartum antibiotic prophylaxis (IAP), has been scarcely investigated, although this practice is routinely used in the group B Streptococcus (GBS) positive women. GBS infection remains one of the major causes of neonatal morbidity and mortality although deaths have declined significantly in the last decade (2001-2011) due to the introduction of IAP. This work is therefore aimed at verifying whether IAP can influence the main microbial groups of the newborn gut microbiota at an early stage of microbiota formation. Methods: 26 infants whose mothers gave positive results to GBS and subjected to IAP with ampicillin (IAP group) were compared to 26 infants whose mothers gave negative results to GBS (control group) were enrolled. Faecal samples were obtained at the age of 1 week. Real-time PCR on DNA extracted from faeces was used to quantify selected microbial groups (Lactobacillus spp., Bidobacterium spp., Bacteroides fragilis group, C. difficile and E.coli). In order to investigate the potential perturbations within the Bidobacterium population that were observed with the real time PCR, PCR-DGGE analyses using genus-specific primers targeted to bifidobacteria were carried out both on the IAP samples and on the controls. Results: The real-time PCR analyses showed that the gut microbiota of the IAP group had a significantly lower counts of bifidobacteria (P= 0.001) with respect to the control group. The other microbial genera and species analysed were not significantly affected by the IAP. Furthermore PCR-DGGE analysis revealed that bifidobacteria were affected by IAP not only quantitatively but also qualitatively. In fact, IAP determined a decrement in the frequency of B. breve (P= 0.003, 25% reduction), B. bifidum (P= 0.003, 25% reduction) and B. dentium (P= 0.001, 25% reduction) with respect to the control group. On the other hand, B. pseudocatenulatum, B. pseudolongum and B. longum seemed to be less influenced by the treatment. Discussion: This study has shown for the first time that IAP has a significant influence on the early bifidobacterial pattern of newborns, both quantitatively and qualitatively. However, the obtained results on a larger number of IAP newborns and the possibility of microbial restoration over time should be considered in future studies.