MULTI-PIPETTE SYSTEM FOR RECOVERY OF LISTERIA SPP. AND SALMONELLA SPP. SIMULTANEOUSLY†

Abstract

Abstract A new rapid method to simultaneously isolate Listeria spp. and Salmonella spp. was developed and evaluated. To construct the Multi-Pipette (MP) method, two pipettes were used to hold 1 mL of selective agar media (one pipette: Modified Oxford, MOX medium for Listeria spp. and the other pipette: Xylose Lysine Decarboxylase, XLD medium for Salmonella spp.). One mL of Brain Heart Infusion broth (BHI) was added onto the selective media through the top of 10 mL pipette. The two pipettes were placed together in a sterilized stomacher bag containing 225 mL of sterilized BHI broth that was used as enrichment broth. Listeria spp. or Salmonella spp. were enriched in the BHI broth and moved up to selective agar medium in the pipettes. They changed the color of the agar and also caused turbidity of the BHI on top of the selective agar. Three treatments were used to evaluate the MP method; (1) L. monocytogenes (10^3–4 CFU/mL), (2) S. typhimurium (10^3–4 CFU/mL), and (3) L. monocytogenes (10^3–4 CFU/mL) and S. typhimurium (10^3–4 CFU/mL) inoculated into enrichment broth with competitors [Escherichia coli (10^6–7 CFU/mL) and Staphylococcus aureus (10^6–7 CFU/mL)]. After 24 h of incubation at 35C, the colors of selective media in the MP (MOX in treatment 1, XLD in treatment 2, and MOX and XLD in treatment 3) were changed to black, and the cultures were isolated from BHI broth in the 10 mL pipettes. This approach is simple, rapid, and economical for simultaneous isolation of motile foodborne pathogens.