Purpose: The purpose of the study was to measure inclusivity and exclusivity characteristics of the method and to assess method performance in testing of various types of environmental samples.
Methods: Inclusivity and exclusivity was determined in testing of target and non-target bacteria in pure culture utilizing enrichment protocols specified for the method. Environmental sample testing consisted of sponge or swab samples taken from five types of environmental surfaces (stainless steel, plastic, ceramic tile, sealed concrete, and rubber) inoculated with Salmonellaspp. and in some cases co-inoculated with a cocktail of competitor bacteria. Performance of the Isothermal Nucleic Acid Amplification method was compared to that of the U.S. FDA reference culture procedure.
Results: Results of inclusivity testing showed that the method is specific for Salmonella spp. and inclusive for serovars of both S. enterica and S. bongori. Of a total of 145 environmental samples tested, there were 69 and 71 samples positive by the Isothermal Nucleic Acid Amplification method after 16 and 24 hours of enrichment, respectively, compared with 68 samples positive by the reference method. For one environmental surface type, stainless steel, there was a significant difference in method performance, in favor of the Isothermal Nucleic Acid Amplificationmethod, as determined by chi-square analysis. Performance of the Isothermal Nucleic Acid Amplification and reference methods was not statistically different for the other four sample types.
Significance: The Isothermal Nucleic Acid Amplification method represents an advance in molecular testing for Salmonella spp. in foods and environmental samples. Single-step enrichment protocols are used, equipment and labor requirements are minimal, and the Isothermal Nucleic Acid Amplification assay can be completed in 30 minutes following enrichment.