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

Abstract

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 ampli? cation of fragment s from bacteria, bifidobacteria and lactobacilli from faecal samples that were collected before and after weaning at the age of approximat ely 1 and 7 months, respectively. The PCR fragment s were subsequently resolved in a sequence-dependen t 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 fragment s in the DGGE profiles it was estimated that breast-fed and formula-fed infants harboured bacterial communities of equal complexity. There was no conspicuou s difference in the distribution of Bifidobacterium or Lactobacillus species between breast-fed and formula-fed infants. The most frequently found representat ives of these gener a 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. Keywords: bifidobacteria , lactobacilli, 16S rDNA, denaturing gradient gel electrophoresis, infant, intestinal microbiota.