Vitamin C Enhances the Antibacterial Activity of Honey against Planktonic and Biofilm-Embedded Bacteria

Abstract

Multifactorial antibacterial action is an important feature of honey; however, its bactericidal efficacy against biofilm-embedded bacteria is limited. The aim of this study was to investigate the impact of vitamin C (Vit C) on the antibacterial activity of natural honeys against planktonic as well as biofilm-embedded bacterial pathogens. The antibacterial activity of four honey samples supplemented with Vit C was expressed as the minimum inhibitory concentration (MIC). At sub-MICs, Vit C significantly increased the antibacterial activity of the tested honeys against Pseudomonas aeruginosa in planktonic cultures. However, after supplementation, honeydew honey, the most active honey, was ineffective against Staphylococcus aureus. On the other hand, when 100% honeydew honey was supplemented with Vit C (100 mg/g of honey) in a multispecies wound biofilm model, complete eradication of almost all bacterial isolates, including S. aureus, was observed. Furthermore, a mixture of honey and Vit C was partially effective against Enterococcus faecalis, whereas honey alone exhibited no antibacterial activity against this bacterium. Vit C counteracted hydrogen peroxide in honey solution and, thus, eliminated the major antibacterial compound present in honey. It is likely that a combination of honey with Vit C may trigger the intracellular production of reactive oxygen species in bacterial cells, but the exact cellular mechanisms warrant further investigations.

Synergistic Antimicrobial Activity of Supplemented Medical-Grade Honey against Pseudomonas aeruginosa Biofilm Formation and Eradication

“…Numerous studies have shown that vitamins C and E exert antimicrobial activity against a wide range of microorganisms, including Staphylococcal species (including Staphylococcus aureus), Streptococcal species, Proteus vulgaris, Escherichia coli, Bacillus subtilis, Candida albicans, Pseudomonas aeruginosa, and Klebsiella pneumoniae [50][51][52][53]. In addition, these vitamins can have synergistic effects with antibiotics and enhance growth inhibition and the lethal effects of antibiotics against microorganisms [40,50,[54][55][56][57][58][59][60][61][62][63]. Recent studies emphasize that vitamins C and E can also enhance the antimicrobial activity of honey [24,37,38,50].…”

“…In addition, these vitamins can have synergistic effects with antibiotics and enhance growth inhibition and the lethal effects of antibiotics against microorganisms [40,50,[54][55][56][57][58][59][60][61][62][63]. Recent studies emphasize that vitamins C and E can also enhance the antimicrobial activity of honey [24,37,38,50].…”

“…Vitamin C is also involved in bacterial metabolism; whereas several bacteria can ferment vitamin C, others cannot result in oxidative stress that will inhibit bacterial growth [64]. Vitamin C likely triggers the intracellular production of reactive oxygen species in bacterial cells [50]. In addition, vitamin C alters the bacterial cell surface to render it increasingly permeable to antibiotics and potentiate the antimicrobial activity [53].…”

“…Moreover, the transition of microorganisms from a planktonic to a biofilm-sessile state thrives under oxidative stress, and therefore antioxidants, such as vitamins C and E, could be a potent complementary therapy [67]. A recent study showed that the supplementation of different types of honey with vitamin C resulted in a significant enhancement of the antibacterial activity against Pseudomonas aeruginosa and Escherichia coli in a dose-dependent manner [50]. In addition, in a multispecies biofilm model with four bacterial species (Staphylococcus aureus, Streptococcus agalactiae, Pseudomonas aeruginosa, and Enterococcus faecalis), vitamin C enhanced the antibiofilm effect of honeydew honey against all four isolates within 24 h [50].…”

“…A recent study showed that the supplementation of different types of honey with vitamin C resulted in a significant enhancement of the antibacterial activity against Pseudomonas aeruginosa and Escherichia coli in a dose-dependent manner [50]. In addition, in a multispecies biofilm model with four bacterial species (Staphylococcus aureus, Streptococcus agalactiae, Pseudomonas aeruginosa, and Enterococcus faecalis), vitamin C enhanced the antibiofilm effect of honeydew honey against all four isolates within 24 h [50]. Although the antibacterial effects of vitamin C may be both bacterial strain-and concentration-dependent [50], these findings suggest a broad range of antimicrobial activity.…”