Intrapartum antibiotic prophylaxis for GBS infection

Recent and planned studies are focused on the evaluation of other potential risk factors during pregnancy and after early infancy. Intrapartum antibiotics are extensively used worldwide for the prevention of maternal infection associated with C/S birth and prevention/management of Group B streptococcal (GBS) infections.

Stearns et al.’s recent study, which was published in Scientific Reports (2017) [1], entitled “Intrapartum antibiotics for GBS prophylaxis alter colonization patterns in the early infant gut microbiome of low risk infants”, is an important example of the effects of antibiotics on intestinal microbiota composition in healthy, term, breastfed infants. In this study, the authors investigated the microbiota composition in 53 infants born vaginally, with no exposure to antibiotics; of these, 14 infants were exposed to intrapartum antibiotic prophylaxis for Group B Streptococcus, and seven infants were born by C-section (in Canada). Overall, the intestinal microbiota of infants born vaginally without exposure to intrapartum antibiotic prophylaxis differed significantly from that of infants born vaginally but exposed to intrapartum antibiotic prophylaxis for GBS or infants born by C-section (also exposed to IAP).

Regarding the results of this study, the faecal microbiota of intrapartum antibiotic prophylaxis-exposed infants exhibited significantly lower alpha diversity, and intrapartum antibiotic prophylaxis for GBS exposure during vaginal birth might therefore affect the Bifidobacterium levels/ predominance (delay in expansion) over the first 12 weeks of life. This study also showed that colonization of the infant gut microbiota differs in the distribution of bacteria, similar to the majority of published studies on the effect of delivery mode on infant intestinal microbiota composition.

This study found that intrapartum antibiotic prophylaxis for GBS affected all aspects of gut microbial ecology including species richness, diversity, community structure, and the abundance of colonizing bacterial genera. These study results also showed that antibiotic prophylaxis for any purpose may affect infant intestinal microbiota composition and this highlights the importance of appropriate antibiotic use.

In 2016, Cassidy-Bushrow and colleagues published a report on an association between maternal Group B streptococcus and infant gut microbiota [2]. In this study, as part of a population-based, general- risk birth cohort, stool specimens were collected from infants’ diapers at one and six months of age. The authors showed that maternal GBS status was statistically significantly associated with gut bacterial composition in the sixth month, and infants of GBS positive mothers were significantly enriched for Clostridiaceae, Ruminococcoceae, and Enterococcaceae also in the sixth month. In addition, Mazzola et al. demonstrated the short-term consequences of maternal intrapartum antibiotic prophylaxis, to prevent GBS infection, on the faecal microbial population in infants, particularly in breastfed infants [3]. The long-term effects on intestinal microbiota composition have not been addressed in previous studies.

Altered microbiota composition has been associated with obesity, allergy, inflammatory bowel disease, and colon cancer, and further studies are needed to define causal effects. These results also highlight the unmet medical need for maternal immunization using potential GBS vaccines.