ISO 16140 Extension Study of the a Method for Detection of Salmonella in 375 g Raw Beef and Raw Veal Samples

Introduction: The VIDAS^® UP Salmonella (SPT) assay is a specific phage protein ligand assay performed in the automated VIDAS instrument in conjunction with a 1-step enrichment procedure. The method has previously been ISO 16140 certified by AFNOR Certification for detection of Salmonellain all 25 g food samples.

Purpose: The objective of this study was to extend the application to 375 g sample size of raw beef and raw veal samples .

Methods: Samples (375 g), ¼ diluted in pre-warmed supplemented Buffered Peptone water, were enriched for 22-26 hours at 41.5±1°C. Two protocols were tested, one with the addition of vancomycin and the other with the addition of the proprietary salmonella supplement. After incubation, samples were boiled for 5 ±1 minutes before performing the assay. All presumptive positive samples were further confirmed after streaking on a chromogenic agar plate. This new method was compared with the ISO 6579 reference method, according to the ISO 16140 standard.

Results: In the comparative study, 63 confirmed positive samples were detected by the new method and 66 with the reference method. No statistically significant difference (X² < 3.84) was observed between both the methods.  Using spiked samples with a strain of Salmonella Ohio, the 50% level of detection was found between 0.3 and 0.9 CFU/375g for the reference method and between 0.2 and 0.8 CFU/375g for the immunoassay method.

Significance: The results of this study demonstrated equivalence of the method with the traditional reference methods for the detection of Salmonella in 375g raw beef and raw veal samples. The ¼ dilution of the matrix into the enrichment broth is an advantage in terms of cost, handling weight for the technician and requirement of space in the incubator.