Performance of a New Molecular Platform for the Recovery and Detection of Salmonella spp. from Fresh Raspberries

Introduction: Molecular methods are of interest for the food industry because the benefit of obtaining results in a relatively short time compared with traditional culture methods. The 3M™ Molecular Detection System combines two technologies: Isothermal DNA Amplification, which uses multiple, specific primers targeting distinct regions of the genome, and Bioluminescence real-time detection. The wide variety of food commodities requires proper validation of alternative methods for Salmonella detection.

Purpose:  The purpose of this study was to compare the recovery of Salmonellafrom inoculated fresh raspberries with the 3M™ Molecular Detection System and traditional culture method.

Methods:  Salmonella spp. strains isolated from berries farm environments (S. Branderup, S. Montevideo, S. Anatum, S. Infantis, S. Agona and S. Poona) were used to inoculate raspberries at 1-5 CFU/25g. Additionally, uninoculated fruit portions were tested. Samples were analyzed according the Food and Drug Administration´s Bacteriological Analytical Manual and 3M Molecular Detection System (MDS) methods. Sample preparation (soak and stomaching) for pre-enrichment step was also evaluated. Data between recovery methods were compared using McNemar’s test for paired data at significant level of 0.05.

Results: Salmonella spp. were recovered from all soak samples with the 3M™ Molecular Detection System and traditional culture method. All stomached samples yielded negative results by both methods. False-positive results were not obtained.

Significance:   The 3M™ Molecular Detection Assay Salmonella can be implemented for the suitable recovery of Salmonella spp. from raspberries. Homogenization of pre-enrichment broth/sample produces false-negative results with either traditional culture methods or 3M™ Molecular Detection System.