DOUBLE-PIPETTE METHOD FOR SELECTION OF MOTILE FOODBORNE PATHOGENS (LISTERIA MONOCYTOGENES OR SALMONELLA TYPHIMURIUM) FROM MIXED CULTURE SYSTEMS†

Abstract A rapid and simple method using two pipettes was developed to determine the presence of Listeria monocytogenes/Listeria spp. or Salmonella typhimurium/Salmonella spp. in mixed cultures. This method involved the following steps. A 10 mL pipette with a sealed tip was used for the enrichment phase. Lactose broth for Salmonella spp., and Universal preenrichment broth for Listeria spp. were used as enrichment broth. The broth was inoculated with a mixture of target organisms with Escherichia coli and Staphylococcus aureus as competitive bacteria and added directly into the 10 mL pipette. Three tenth (0.3 mL) of selective agar media (MOX for Listeria monocytogenes and XLD for Salmonella typhimurium) were placed in a 1 mL pipette. After solidification, BHI broth was added on top of the selective medium. Then, the 1 mL pipette was inserted into the 10 mL pipette to provide the combination of enrichment and selective procedures. The top of the large pipette was sealed with sterilized Parafilm, and the apparatus was incubated at 37C for 24 h. Following the growth of the motile foodborne pathogens (L. monocytogenes or S. typhimurium) in enrichment broth placed in the 10 mL pipette, these organisms moved into the selective agar medium causing characteristic changes in the color of the medium. The results showed high efficiency for recovery of motile foodborne pathogens from mixed culture systems. This new method is developed to be economic, rapid, and a simple way to recover motile foodborne pathogens from food systems.