Antibacterial Activity of Olive Oil Polyphenol Extract Against <i>Salmonella</i> Typhimurium and <i>Staphylococcus aureus</i> : Possible Mechanisms

Abstract

Polyphenols are a group of active ingredients in olive oil, and have been reported to exhibit antioxidant activity. <i>Salmonella enterica</i> subsp. <i>enterica</i> serovar Typhimurium (<i>Salmonella</i> Typhimurium) and <i>Staphylococcus aureus</i> are common foodborne pathogens causing serious infections and food poisoning in humans. This study was conducted to analyze the antibacterial activity of olive oil polyphenol extract (OOPE) against <i>Salmonella</i> Typhimurium and <i>S. aureus</i>, and reveal the possible antibacterial mechanism. The antibacterial activity was estimated using minimum inhibitory concentration (MIC) values and bacterial survival rates when treated with OOPE. The antibacterial mechanism was revealed through determinations of changes in intracellular ATP concentration and cell membrane potential, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and transmission electron microscopy analysis. The results showed the MICs of OOPE against <i>Salmonella</i> Typhimurium and <i>S. aureus</i> were 0.625 and 0.625-1.25 mg/mL, respectively. The growth of <i>Salmonella</i> Typhimurium and <i>S. aureus</i> (∼8 log CFU/mL) was completely inhibited after treatments with 0.625 mg/mL of OOPE for 3 h and 0.625-1.25 mg/mL for 5 h, respectively. When <i>Salmonella</i> Typhimurium and <i>S. aureus</i> were exposed to OOPE, the physiological functions associated with cell activity were destroyed, as manifested by reduction of intracellular ATP concentrations, cell membrane depolarization, lower bacterial protein content, and leakage of cytoplasm. These findings suggested a strong antibacterial effect of OOPE against <i>Salmonella</i> Typhimurium and <i>S. aureus</i>, and provided a possible strategy of controlling contamination by these two pathogens in food products.