Diversity of Bifidobacterium and Lactobacillus spp. in Breast-Fed and Formula-Fed Infants as Assessed by 16S rDNA Sequence Differences

A qualitative molecular monitoring approach based on PCR and denaturing gradient gel electrophoresis (DGGE) was used to study the diversity of dominant bacteria, bifidobacteria and lactobacilli in vaginally delivered full-term infants. Seven breast-fed and six formula-fed infants participated in the study. 16S rDNA targeted primers were used for the specific PCR amplification of fragments from bacteria, bifidobacteria and lactobacilli from faecal samples that were collected before and after weaning at the age of approximately 1 and 7 months, respectively. The PCR fragments were subsequently resolved in a sequence-dependent manner by DGGE. In addition, cloning and sequence analysis of the PCR fragments was used to identify the species from which they originated. Based on the number of fragments in the DGGE profiles it was estimated that breast-fed and formula-fed infants harboured bacterial communities of equal complexity. There was no conspicuous difference in the distribution of Bifidobacterium or Lactobacillus species between breast-fed and formula-fed infants. The most frequently found representatives of these genera were B. infantis and species belonging to the L. acidophilus -group in both groups of infants. The predominant Bifidobacterium and Lactobacillus populations in most infants consisted of only one or two species.