The selective inhibition of tannic acid against certain intestinal pathogenic bacteria could be explained by strong iron binding capacity of tannic acid. Aerobic microorganisms need iron for several functions, including reduction
of ribonucleotide precursor of DNA and to form heme group. Iron is not considered a stimulatory growth factor of some lactobacilli because they lack heme enzymes and the most relevant ironcontaining ribonucleotide reductase has been replaced with an enzyme using adenosylcobalamine