Gut colonisation with bifidobacteria in early infancy is essential for the well-being of the infant. Gestational age and mode of delivery are among the factors influencing the colonisation process. The aim was to characterise the bifidobacterial composition in the gut of one-month-old full-term and pre-term Brazilian infants, both being delivered vaginally or by caesarean section. Fourty nine Brazilian (Vicosa, Minas Gerais state) one-month-old infants were divided in two groups: full-term (n = 24) and pre-term (n = 25), and compared to each other. Each group was then characterised according to its mode of delivery. Infant stool samples were available for bifidobacterial characterisation by quantitative polymerase chain reaction (qPCR) method. All study infants were colonised by bifidobacteria. Bifidobacterium longum colonised all full-term and pre-term newborns. Differences were observed in counts of Bifidobacterium genus and Bifidobacterium longum between full-term and pre-term infants (8.8 log cells/g, IQR 7.9-9.1 vs. 7.1 log cells/g, IQR 6.6-8.6, p = 0.02 and 8.3 log cells/g, IQR 6.7-9.1 vs. 6.4 log cells/g, IQR 6.1 -6.7, p = 0.001, respectively). Furthermore, the prevalence of Bifidobacterium lactis differed between pre-term caesarean and pre-term vaginally born infants (50.0% vs. 93.8%, p = 0.023). Gut bifidobacterial composition of one-month-old full-term infants differs from that of pre-term newborns in Vicosa, Minas Gerais state, Brazil. Gestational age is a factor influencing bacterial numbers and species, while mode of delivery have an impact on the prevalence and quantity of bifidobacteria in studied infants. Bifidobacteria may have an impact on later health of the infants and the species B. longum and B. lactis might provide clues on the potential probiotic applications in pre-term newborns at the risk of developing postnatal complications. (C) 2015 Elsevier Ltd. All rights reserved.