Identification of Staphylococcus Aureus in Foods by the Warnex™ Semi-quantitative Real-time Polymerase Chain Reaction System

- 1/3 -

1. Application

This method is applicable to the qualitative detection of Salmonella spp. in food and environmental samples.

It is a suitable screening test, especially where follow up product action is not anticipated. When product- based compliance action is anticipated, and where stipulated, the Official Methods and HPB Method should be used.

2. Description

The method has proven to be effective in the detection of Salmonella spp. in a wide variety of artificially- contaminated foods in internal validation studies by the manufacturer (10.1-10.3) and in an AOAC interlaboratory collaborative study (10.4). In addition, the method has been validated with naturally- contaminated foods in comparative and collaborative studies in HPB laboratories (10.5-10.6). It is Noted that an alternative enrichment scheme, different from that recommended by the manufacturer was successfully tested in the HPB studies and appears in this Laboratory Procedure.

3. Principle

The DNA hybridization test employs Salmonella-specific DNA probes and a colorimetric system for the detection of Salmonella spp. in test samples following broth culture enrichment. Probes used in the assay are reactive with serovars belonging to all subspecies of Salmonella enterica and with serovars belonging to the separate species Salmonella bongori. A sample is considered non-reactive for Salmonella spp. if the absorbance (A₄₅₀) of the test sample is less than or equal to the established cutoff value for the assay. A sample is considered presumptively positive for Salmonella spp. if the absorbance value is greater than the established cutoff value for the assay. Reactive samples must be confirmed by standard cultural procedures followed by biochemical and serological identification.

4. Definition of Terms

See Appendix A of Volume 3.

5. Collection of Samples

See Appendix B of Volume 3.