Salmonella species are a major cause of foodborne infection. Food producers have therefore developed stringent control measures to prevent Salmonella contamination by monitoring for this pathogen wherever food is handled during processing, including on the production line. In order to improve food safety, producers monitor for compliance with hygiene standards, but for this control to be effective, microbiological testing procedures must be accurate, sensitive and preferably rapid.
For these reasons, the Thermo Scientific™ SureTect™ Salmonella species PCR (polymerase chain reaction) Assay is a valuable asset in any food safety laboratory. Assay reagents are supplied in pre-dispensed kit form to simplify and improve assay handling. Furthermore, designated assay software controls each assay run, providing a clear read out of assay data.
As a part of the product testing procedure, scientists from Thermo Fisher Scientific in conjunction with colleagues from an independent laboratory carried out a comparison of the performance of the real-time SureTect Salmonella species PCR Assay with the reference method detailed in ISO 6579:20021. Using samples gathered from food production environments, the team analyzed the microbial populations for presence of Salmonella species using each of the two methods.
The samples obtained for the comparison included siphon, process and rinse waters, surface sampling wipes, and dust. The scientists added pre-determined amounts of these to Buffered Peptone Water and incubated them for 20 hours at 37°C to enrich the cultures. Following this, samples underwent lysis before running in the SureTect PCR assay using a Thermo Scientific SureTect PikoReal™ Real-Time PCR instrument. Positive results, automatically interpreted using the assay software, were confirmed using the SureTect confirmation protocol. This involves subculture in RVS broth with subsequent plating onto Brilliance™ Salmonella Agar. From this, presumptive positive colonies (purple in color) are confirmed using either the Thermo Scientific Oxoid™ Salmonella latex kit or the Thermo Scientific Oxoid™ Microbact GNB 24E biochemical kit.
The team analyzed 30 positive and 44 negative samples. Of the positive samples, three were naturally contaminated and the remainder spiked with dilutions of stressed isolates of representative Salmonella serotypes (Amsterdam, Typhimurium, Agona, Blockley and Indiana). Samples underwent analysis using both the SureTect method and the ISO 6579:2002 reference method.
The SureTect Salmonella PCR assay correctly identified 28 of the 30 positive samples, with additional confirmation using either latex agglutination or biochemistry. This included samples spiked at low dilutions of the stressed isolates. The two samples not identified by PCR did show positive results using the confirmation tests, and the scientists note that pre-analysis enrichment may have been beneficial.
Compared to the reference method detailed in ISO 6579:2002, the scientists found that the SureTect Salmonella species PCR assay performed satisfactorily and they conclude that this kit is a suitable alternative as a rapid method for checking for Salmonella species in production environment samples.