Purpose: To evaluate the use of a combined surface extraction and filtration approach for removal and concentration of Salmonella from artificially contaminated stainless steel surfaces prior to molecular detection; to compare this approach with traditional swab-based sampling methods.
Methods: Salmonella Typhimurium ATCC 14028 was diluted in PBS and a total of 106 CFU were distributed evenly over the surface of small (4” x 4”) or large (24” x 4”) stainless steel plates (type 304, #4 finish). After drying, contaminated surfaces were sampled using three methods: cotton swab, rayon swab and foam/vacuum surface extraction plus hollow fiber concentration (E+C). Salmonella recovery with each method was assayed by quantitative PCR (qPCR) targeting the invA gene.
Results: For small plates, use of the E+C method led to a 10-fold increase in recovery of S. Typhimurium over the swab-based methods. Sampling efficiency was higher for the larger plates, where the E+C method yielded a 100-fold increase in recovery of S. Typhimurium over the swabs. Lower recovery from the smaller plates was attributed to difficulties in maintaining a vacuum seal with the sample surface, as the dimensions of these plates were similar to those of the extractor sampling head.
Significance: Combined use of foam-based vacuum extraction and subsequent hollow fiber concentration enabled enhanced recovery of S. Typhimurium from a model food processing surface compared to traditional swab-based methods, allowing concentration of contaminant cells from bulk surfaces into small sample volumes compatible with molecular testing methods such as qPCR.