Variation in recovery of Salmonella strains extracted from leafy greens

This study investigated the degree of extraction from leafy green tissue (green leafy lettuce, spinach, red cabbage) artificially inoculated with five individual strains of Salmonella at 3-4 log CFU. Inclusion of salt at levels of 0.50 M-0.75 M in the extraction solution improved recovery of S. Enteritidis Benson (P < 0.05) but salt in the range of 0.09-0.75 M had no effect on S. Enteritidis ME18, S. Newport, S. Oranienburg, and S. Typhimurium. Salmonella strain had a significant effect on extraction efficiency from lettuce tissue (P < 0.05) with Newport (68.7%) and Oranienburg (18.7%) exhibiting the highest and lowest recoveries, respectively. Recoveries were statistically higher in spinach than in green leafy lettuce or red cabbage (P < 0.05); however, S. Enteritidis ME18, S. Newport, and S. Typhimurium exhibited the same order of extractability in all three tissue types. Repeated extraction of spinach tissue continued to recover Salmonella in each extraction step. After extracting lettuce tissue multiple times, Salmonella was not detected in 25-g samples subjected to enrichment culture when 100 cells were initially applied. Continued detection of Salmonella occurred in extracted tissue when 400 cells of the pathogen were initially applied to the tissue.