Synergistic inhibition of Listeria monocytogenes by nisin and garlic extract Original Research Article

Minimum Inhibitory Concentrations (MICs) were determined for nisin and an aqueous garlic extract (AGE) for six strains of Listeria monocytogenes, including a nisin-resistant mutant. When used in combination in broth a synergistic effect was observed between nisin and AGE in all strains. Increasing the pH reduced the activity of both nisin and garlic. During storage of the aqueous garlic extract at 4°C and at 20°C for 14 days, the MIC increased over the first 8 days but remained stable thereafter, indicating at least two antimicrobial components, one of which was relatively stable. Aqueous garlic extract was not appreciably bactericidal although there was a positive interaction with nisin in terms of its bactericidal effect in broth at 4°C. The effect of combining nisin and garlic in a food system, hummus, was also studied. Sub-MIC combinations of AGE and nisin were effective at preventing listerial growth and did enhance the slight bactericidal effect of nisin. The results indicate that combined use of nisin with garlic could help overcome problems of nisin resistance in Gram-positive organisms. Such interactions could also be a significant factor in traditional lactic fermented foods where garlic is an ingredient.