Concentration of the Foodborne Pathogen Salmonella from Complex Spice Samples for Molecular Diagnostics Using the InnovaPrep Concentrating Pipette

Introduction: The Food and Drug Administration has recently reported that approximately 7% of imported spices are contaminated with the foodborne pathogen, Salmonella.  Detection and identification of pathogens by molecular diagnostics can provide accurate results in significantly shorter time periods, but further improvement in sensitivity is attained through concentration of the target organism(s).

Purpose: The purpose of this study was to evaluate and validate the performance of the InnovaPrep Concentrating Pipette as a tool for the concentration of Salmonella from complex spice samples.

Methods: Ten common spices were collected from bulk spice markets.  These samples were cultured for 24 hours in 50 ml of Buffered Peptone Water as described in the USDA Salmonella protocol (sample to media ratio: 1/100).  One ml samples were collected from the cultures (n = 3) for DNA extraction using the SureTec sample preparation chemistry and protocol.  Cultures that tested positive (n = 4; turmeric, thyme, black pepper, and oregano) where processed using the Concentrating Pipette.  The remaining culture media (47 mls) was processed with a 0.4 micron polycarbonate Concentrating Pipette Tip using the concentrator and was eluted with 200 µl wet foam elution buffer and collected into a sterile tube.  This resulted in a 235:1 concentration of the sample.  Ten microliters of the concentrated sample were then processed for PCR using the SureTec protocol as described above.  Following cell lysis, the samples were amplified using the SureTec Salmonella PCR reagents.

Results: Amplification showed a significant improvement in crossing threshold cycle number to determine a positive result.  Salmonella-positive spice samples (n = 4) showed a mean improvement of  15 cycles to achieve a positive result (23 cycles). 

Significance: This study demonstrates the utility of the InnovaPrep Concentrating Pipette for the cleanup and concentration of Salmonella from complex spice samples.