SPECIFIC DETECTION AND ANALYSIS OF A PROBIOTIC BIFIDOBACTERIUM STRAININ INFANT FECES

For specific detection of the probiotic Bifidobacterium sp. strain LW4 20 in infant feces and for rapid quality control of this strain in cul ture, three strain-specific 16S rRNA gene-targeted primers have been d eveloped. These primers allow specific detection of the organism via P CR. Specificity of the primers was determined in DNA samples isolated from single-strain and mixed cultures of bifidobacteria and in heterog enous fecal samples. The feasibility of this method for use in specifi c detection of probiotic strains was investigated through addition of Bifidobacterium sp. strain LW420 to infant instant milk formula (IMF) and PCR analyses of bacterial DNA isolated from feces of 17 newborn IM F-fed infants. In feces of all nine babies that had been fed with the probiotic IMF, the strain-specific PCR signal could be detected. No si gnal was found in feces of the eight infants that had been fed with a nonprobiotic IMF, demonstrating the specificity of the PCR method. All 17 infants developed a major fecal Bifidobacterium population already after 3 days, as determined through genus-specific and strain-specifi c PCR. Phenotypical screening of Bifidobacterium sp. strain LW420 and analysis of homology of the 16S rRNA gene sequence of this strain with that of other bifidobacteria deposited in databases do not allow posi tive classification of LW420 among the currently known species of Bifi dobacterium.