Total phenolic content, antiradical, antimicrobial and antibiofilm properties of grape and apple vinegar

Antimicrobial resistance – the capability of microorganisms to resist antimicrobial agents – has been stated as a major concern for public health. The increase in spread of multi- and pan-resistant bacteria which are not treatable with present antimicrobials has brought the need for the use of alternative products. Vinegar is a natural product- produced from alcoholic fermentation- that has shown strong antimicrobial activity. The aim of this study was to determine the total phenolic content and antiradical activity of the commercial grape and apple vinegar as well as to evaluate their antibiofilm and antimicrobial activities against Staphylococcus aureus and Pseudomonas aeruginosa. Grape vinegar showed higher total acidity and total phenolic content, and lower antiradical activity (DPPH activity) compared to apple vinegar. The populations of S. aureus and P. aeruginosa were significantly reduced by neat grape and apple vinegar samples. The antibacterial activity of grape vinegar was superior to apple vinegar. While AV and GV samples at 50% concentration did not form a visible zone of inhibition against S. aureus, they showed an inhibitory effect against P. aeruginosa (16.24 mm for GV and 16.5 for AV). The vinegar applied at the lowest concentration (25%) did not show any antibacterial effect on either bacterium. Solutions containing 50% to 6.25% vinegar samples prevented almost 100% biofilm formation in both bacteria. However, solutions containing lower amounts of vinegar showed stronger inhibition of biofilm formation by P. aeruginosa. A positive correlation was found between the biofilm reducing ability of vinegar samples and their antibacterial activity in this study. Taken together, commercial grape and apple vinegar significantly reduced the viability of S. aureus and P. aeruginosa, thereby decreasing biofilm formation.