NISIN and gilaburu (Viburnum opulus L.) combination is a cost-effective way to control foodborne Staphylococcus aureus

Abstract

This study aims to elucidate the inhibitory activity of nisin alone or in combination with gilaburu (Viburnum opulus L.) against the foodborne Staphylococcus aureus. The effect of nisin and gilaburu on the growth of S. aureus was investigated under different pH (5-7) and salt concentrations (NaCl, 0.5-4.5% w/v) at 30 degrees C. Nisin exhibited the best antibacterial activity at pH 5 with a minimum inhibitory concentration (MIC) of 25 mu g/mL, while its MIC was 50 mu g/mL in all salt concentrations when the pH was kept constant at pH 7. The MIC of gilaburu was found to be 50% in all conditions studied. The minimum bactericidal concentrations (MBC) of nisin and gilaburu were 100 mu g/mL and >50%, respectively. Changes in pH and salt concentrations did not affect MBC. According to checkboard assay results, a synergy was found between gilaburu and nisin (FIC = 0.25) for both 2.5% and 4.5% w/v salt concentrations at pH 5. The synergistic interaction between nisin and gilaburu was also studied using an agar disk diffusion assay where nisin concentration was kept constant at 3.125 mu g/ml, while gilaburu concentration varied between 3.125 and 100%. The positive effect of gilaburu on nisin activity was further confirmed by time-kill assay, flow cytometry, and measurement of relative TTC dehydrogenase activity and conductivity as well as DNA and protein leakage. In conclusion, nisin combined with gilaburu exerted the same inhibitory effect on S. aureus at a concentration approximately 8 times lower than that of MIC of nisin alone (25 mu g/mL). This study shows the potential use of nisin and gilaburu in combination to control S. aureus in food.