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Abstract
The present study was undertaken to determine the mechanism of antibacterial activity
of a polyphenolic fraction, composed of mainly catechin and isorhamnetin, previously
isolated from Kombucha, a 14-day fermented beverage of sugared black tea, against
the enteropathogen Vibrio cholerae N16961. Bacterial growth was found to be seriously
impaired by the polyphenolic fraction in a dose-dependent manner. Scanning Electron
Microscopy demonstrated morphological alterations in bacterial cells when exposed
to the polyphenolic fraction in a concentration-dependent manner. Permeabilization
assays confirmed that the fraction disrupted bacterial membrane integrity in both
time- and dose-dependent manners, which were proportional to the production of intracellular
reactive oxygen species (ROS). Furthermore, each of the polyphenols catechin and isorhamnetin
showed the ability to permeate bacterial cell membranes by generating oxidative stress,
thereby suggesting their role in the antibacterial potential of Kombucha. Thus, the
basic mechanism of antibacterial activity of the Kombucha polyphenolic fraction against
V. cholerae involved bacterial membrane permeabilization and morphological changes,
which might be due to the generation of intracellular ROS. To the best of our knowledge,
this is the first report on the investigation of antibacterial mechanism of Kombucha,
which is mostly attributed to its polyphenolic content.