This study investigates the succession of bacterial communities in the intestines of two healthy human neonates using molecular techniques. The researchers monitored 16S rDNA diversity in fecal samples through PCR and denaturing gradient gel electrophoresis (DGGE), and analyzed the sequences of major ribotypes. The results showed that the bacterial communities in both infants became more complex over time, with dominant populations including Bifidobacterium, Ruminococcus, Enterococcus, Clostridium, and Enterobacter. However, 19 of 34 cloned rDNA sequences exhibited less than 97% identity with known bacterial sequences. The study demonstrated that combining PCR-DGGE with 16S rDNA sequence analysis provides a dynamic description of bacterial colonization in the infant intestinal ecosystem, allowing visualization of bacteria difficult to cultivate or detect by other methods. The study also highlights the differences in bacterial colonization between breast-fed and formula-fed infants. Breast-fed infants rapidly develop a microbiota dominated by bifidobacteria, while formula-fed infants have a more diverse microbiota. The succession of bacterial communities continues until after weaning, when a stable, complex microbiota is established. Traditional culturing methods have been used to study infant gut microbiology, but molecular techniques offer more accurate and comprehensive insights into the biodiversity of the gastrointestinal ecosystem. The study used molecular techniques to analyze the fecal microbiota of two infants, revealing the dynamic changes in bacterial communities over time. The DGGE profiles showed that the microbiota of both infants became more complex as they grew, with different bacterial species dominating at different stages. The study also identified several bacterial species that were not previously known in the human intestinal microbiota. The results suggest that molecular techniques such as PCR-DGGE and 16S rDNA sequence analysis are valuable tools for studying the development and succession of bacterial communities in the infant gut. These techniques allow for the identification of bacterial species that are difficult to cultivate, providing new insights into the role of the microbiota in infant health and development.This study investigates the succession of bacterial communities in the intestines of two healthy human neonates using molecular techniques. The researchers monitored 16S rDNA diversity in fecal samples through PCR and denaturing gradient gel electrophoresis (DGGE), and analyzed the sequences of major ribotypes. The results showed that the bacterial communities in both infants became more complex over time, with dominant populations including Bifidobacterium, Ruminococcus, Enterococcus, Clostridium, and Enterobacter. However, 19 of 34 cloned rDNA sequences exhibited less than 97% identity with known bacterial sequences. The study demonstrated that combining PCR-DGGE with 16S rDNA sequence analysis provides a dynamic description of bacterial colonization in the infant intestinal ecosystem, allowing visualization of bacteria difficult to cultivate or detect by other methods. The study also highlights the differences in bacterial colonization between breast-fed and formula-fed infants. Breast-fed infants rapidly develop a microbiota dominated by bifidobacteria, while formula-fed infants have a more diverse microbiota. The succession of bacterial communities continues until after weaning, when a stable, complex microbiota is established. Traditional culturing methods have been used to study infant gut microbiology, but molecular techniques offer more accurate and comprehensive insights into the biodiversity of the gastrointestinal ecosystem. The study used molecular techniques to analyze the fecal microbiota of two infants, revealing the dynamic changes in bacterial communities over time. The DGGE profiles showed that the microbiota of both infants became more complex as they grew, with different bacterial species dominating at different stages. The study also identified several bacterial species that were not previously known in the human intestinal microbiota. The results suggest that molecular techniques such as PCR-DGGE and 16S rDNA sequence analysis are valuable tools for studying the development and succession of bacterial communities in the infant gut. These techniques allow for the identification of bacterial species that are difficult to cultivate, providing new insights into the role of the microbiota in infant health and development.