Unraveling a mechanism of honey antibacterial action: Polyphenol/H2O2-induced oxidative effect on bacterial cell growth and on DNA degradation

Abstract Several compounds with antibacterial activities were identified in honey however, a mechanism by which they lead to bacterial growth inhibition and bacterial death remains still unknown. We recently found that honeys possess DNA degrading activity mediated by honey hydrogen peroxide and an unknown honey component(s). Here we provide evidence that active honeys (MIC 90 of 6.25–12.5% v/v) possessed significantly higher levels of phenolics ( p p 2 O 2 by catalase eliminated bacteriostatic activities caused by both phenolics and H 2 O 2 suggesting that the growth inhibition resulted from the coupling chemistry between these compounds. Both phenolics and H 2 O 2 were involved in DNA degradation by honeys. Treatment of plasmid DNA with H 2 O 2 alone did not affect the DNA integrity but H 2 O 2 removal from honey by catalase prevented DNA degradation. Polyphenols extracted from honeys degraded plasmid DNA in the presence of H 2 O 2 and Cu(II) in the Fenton-type reaction. The extent of DNA degradation was inversely related to the polyphenol concentration in this system as well as in honeys. At low content, honey polyphenols exerted pro-oxidant activity damaging to DNA. In conclusion, honey phenolics with pro-oxidant activities were necessary intermediates that conferred oxidative action of H 2 O 2 . Phenolic/H 2 O 2 -induced oxidative stress constituted the mechanism of honey bacteriostatic and DNA damaging activities.