Background and Aims Group B Streptococcus (GBS) early-onset bacterial sepsis is an important cause of neonatal morbidity and mortality. In the last decade, after the introduction of intrapartum antibiotic prophylaxis in pregnant women during labor and delivery, the sepsis-associated death rates have declined. The aim of this study is to evaluate the effects of antibiotic treatment of pregnant women GBS-positive on early colonization of bacteria in the newborn gut, which is known to be related to immunity development.

Methods Thirty-four vaginal delivered and breastfed newborns were enrolled; 17 had mothers GBS-positive treated with 2g of Ampicillin and 17 had mothers GBS-negative (control group).

Two-hundred milligrams faeces were collected for each subject and processed for DNA extraction, performed with QIAamp DNA Stool Mini Kit [Qiagen, Cat. No. 51504]. Lactobacillus spp., Bidobacterium spp., Bacteroides fragilis group, C. difficile and E. coli quantification was obtained with real-time PCR. Data of microbial counts were subjected to one-way variance analisys in order to evidence significant differences between treated and control group of newborns.

Results Antibiotic therapy reduced the intestinal colonization of Bifidobacterium: 5.51 Log(CFU/g) in treated samples against 7.07 Log(CFU/g) in control samples; P<0.05.

All the others microbial genera and species analysed were not affected by the maternal treatment with Ampicillin.

Conclusions Preliminary results showed a decrease of early Bifidobacterium count in the microbiota of newborns; the clinical meaning or the effect on newborn immunity need to be investigated with larger studies.