Comparative Antibacterial Activity of Different Plant Extracts in Relation to their Bioactive Molecules, as Determined by LC-MS Analysis

Abstract. The research of plant responses against antibiotics and chemical disinfectants is increasingly motivated by natural antimicrobial agents. We investigated hydrophilic extracts of leaves of Persian walnut (Juglans regia) and European Mistletoe (Viscum album) and White willow bark (Salix alba) which were characterized by their content in phenolic derivatives, using a high-throughput technique, HPLC-DAD. The extracts were obtained using 10 % dry plant and hot acidulated water (around 850C) and kept for 48 hours then diluted successively (from 2 to 9 times). The antimicrobial activities were tested semi-quantitative ly on agar plates inoculated with E. Coli, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus and Salmonella enteritis. The inhibition zones were measured after 24 hours of incubation. Using a liquid nutrient broth growth medium, a quantitative evaluation of antimicrobial effect was done. There were noticed to be significant the growth rates in the first 10 hours, the best inhibitory results being given by Salix alba extract which inhibited all bacteria. Meanwhile, walnut and mistletoe extracts showed different inhibition rates, depending on the bacteria and the extract dilution. The extracts ’ composition as determined by HPLC was compared with the antimicrobial activity, suggesting that willow extract is the richest in phenolics, especially in phenolic acids (salicylic acid derivatives). This study suggest that Salix alba bark and Juglans regia are available and efficient sources of natural antimicrobials and suggests the possibility of using their hydrophilic extracts as bio-disinfectants in food industry