Abstract
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.
Highlights
Microorganisms are able to grow on food matrixes, food industry equipment, surfaces and biofilm which is an extracellular matrix formed by many different bacteria, including Bacillus spp., Listeria monocytogenes, Staphylococcus spp., Escherichia coli and Pseudomonas aeruginosa in different environments (Giaouris et al, 2015)
While apple vinegar (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 (16.25 mm for GV and 16.50 for AV)
We found that P. aeruginosa was more susceptible to vinegars than S. aureus, which confirms that of previous study reported that gram negatives are more sensitive than positives (Halstead et al, 2015)
Summary
Microorganisms are able to grow on food matrixes, food industry equipment, surfaces and biofilm which is an extracellular matrix formed by many different bacteria, including Bacillus spp., Listeria monocytogenes, Staphylococcus spp., Escherichia coli and Pseudomonas aeruginosa in different environments (Giaouris et al, 2015). The total phenolic content of vinegar samples was determined by using the Folin-Ciocalteu method based on the procedure of Pawar and Dasgupta (2018), and gallic acid (Sigma, USA) was used as a standard. 50 μL of two concentrations (10% and Neat) from each vinegar sample (prepared in distilled water) and 150 μL of the DPPH solution were added to the well of the 96-well plate. The following controls were used for each microplate; positive control: TSB+1% sucrose (145 μL), 0.9% sterile saline solution (55 μL) and bacterial suspension (20 μL); negative control I: TSB+1% sucrose (220 μL); negative control II: TSB+1% sucrose (145 μL) the appropriate vinegar concentration in sterile distilled water (55 μL) and 0.9% sterile saline solution (20 μL). The nonadherent bacteria were removed and the microplate wells were gently washed three times with 250 μL sterile distilled water. Results were expressed as the mean±standard deviation (SD) and values of P
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