Purpose : To reduce the level of E. coli O157:H7, Salmonella spp and Shigella spp in parsley after washing with extracts of edible vegetables.
Methods : Twenty aqueous and ethanolic extracts of edible plants were tested for antimicrobial activity against composite strains of Salmonella, E. coli O157:H7 or Shigella spp using the agar-well assay. The two most active extracts were selected and the minimum bactericidal concentration (MBC) determined. Mixtures of extracts were analyzed for synergistic activity against the strains using the checkerboard method. The mixture with synergism was used to wash 60-g parsley samples previously inoculated (by spot method) with 103 cells/ml. After 0, 1, 3, 5 and 7 days, viable bacterial counts were determined. 200 ppm chlorine, 200 ppm Citrol® and water were used as controls.
Results: Four extracts inhibited all the pathogenic bacteria tested. The extracts E1 and E2 (MBC of 1.5 mg/ml and 4.5 mg/ml, respectively) were selected for further experiments. The mixture (E1: 0.18 mg/ml and E2: 1.25 mg/ml) exhibited synergistic antimicrobial effect against a cocktail of each bacteria and was used for the washing procedures. A reduction of 2 log in E. coli O157:H7 and Shigella spp was observed at the first day and at the third day for Salmonella. These extracts were similar in efficacy to chlorine.
Significance : The extracts of two edible vegetables exhibited antimicrobial activity against Salmonella spp, E. coli O157:H7 and Shigella spp. and could be alternatives to reduce these pathogens in parsley.