Antimicrobial activity of catechol isolated from Diospyros kaki Thunb. roots and its derivatives toward intestinal bacteria

The growth-inhibiting activities of the methanol extract of Diospyros kaki Thunb. roots were examined on the growth of Bifidobacterium breve, B. longum, Clostridium difficile, Clostridium perfringes, Escherichia coli, and Lactobacillus casei. In addition, the biologically active component of D. kaki roots was purified using silica gel column chromatography and HPLC. The active component was characterised as catechol by spectroscopic analyses. The antimicrobial activity of the isolated catechol varied according to the dose and bacterial strains tested. Catechol significantly (++++) inhibited the growth of C. perfringens at 2.0 mg/disc, and moderately (++) inhibited its growth at 0.25 mg/disc. At a dose of 5.0 mg/disc, catechol significantly inhibited the growth of C. difficile and moderately inhibited the growth of E. coli. However, this isolate did not inhibit the growth of bifidobacteria and lactobacilli. When various functional groups were added to the catechol, selective growth-inhibiting activity against harmful intestinal bacteria was observed in response to treatment with low concentrations. Taken together, these findings indicate that D. kaki root-isolated catechol and its derivatives (4-nitrocatechol, 4-tert-butylcatechol, tetrabromocatechol) could be useful as preventive agents against diseases caused by harmful intestinal bacteria.