Purpose: This study evaluated the performance of a real-time PCR assay and the FDA-BAM cultural method for detecting Salmonella on stainless steel and epoxy-coated concrete surfaces. Surface samples were inoculated with Salmonella and a competitor, Citrobacter braakii, then evaluated using two different sponge types enriched in either Buffered Peptone Water (BPW) or Lactose Broth (LB).
Methods: Stainless steel (n = 80) and epoxy-coated concrete (n = 80) surfaces were artificially co-inoculated with either a Salmonella cocktail or Salmonella Newport, respectively, and with a background organism, Citrobacter braakii, to obtain fractional recovery. Each surface was swabbed with one of two sponge types then added to 225 ml of either pre-warmed (35°C) LB or BPW. Samples were incubated at 35 ± 2°C for 22 h before proceeding with BAX® System method testing and reference culture confirmation.
Results: Of the 80 fractionally inoculated stainless steel surfaces, PCR detected 2/20 presumptive positive samples after 22 h of enrichment in BPW using sponge #1 and 7/20 using sponge #2. In LB, 6/20 using sponge #1 and 10/20 using sponge #2 were detected. Of the 80 fractionally inoculated epoxy-coated concrete surfaces, PCR detected 3/20 presumptive positive samples after 22 h of enrichment in BPW using sponge #1 and 7/20 using sponge #2. In LB, 9/20 using sponge #1 and 6/20 using sponge #2 were detected. All positive results were confirmed following the FDA-BAM reference culture method.
Significance: Regardless of sponge type, the results for epoxy-coated concrete and stainless steel environmental samples enriched in either BPW or LB, demonstrate no significant statistical difference as indicated by POD analysis. Overall, the DuPontTM BAX® System Real-Time PCR assay for Salmonella demonstrates equivalence to the reference culture method.