Early Detection of Salmonella spp. Contamination in Raw Beef Meat Samples

Introduction: Salmonella spp. is an important adulterant bacteria found in raw beef meat samples. The cultural methods, based on two successive enrichment steps (MLG 4, ISO 6578), provide a result in 3 and 5 days, for negative and positive samples, respectively. Many alternative qPCR-based methods, certified by AFNOR and/or AOAC, have been developed and typically rely on a short enrichment step (10 ± 2 h) enabling to get a result in 1 to 2 days. 

Purpose: In order to reduce time to result to as short as 4 h, we developed a new protocol using the GeneDisc® PCR based technology from Pall Corporation. 

Methods: Briefly, 78 fresh raw beef samples were spiked with injured Salmonella spp. cells. The spiking dose ranged from 1 CFU/sample to 1 CFU/g and the injury level was comprised between 33 and 79 %. Artificially contaminated samples were enriched in BPW pre-heated at 41.5°C. Enriched samples were collected every hour from 2 to 5 h incubation to perform qPCR analyses. Confirmation of presumptive positive samples was done by sub-culturing in RVS then plating onto XLD agar media or direct plating.

Results: Results highlighted that the sample type, the Salmonella strain or its injury level had no impact on the enrichment time. Thus, the enrichment time for the detection of Salmonella spp. in raw beef samples only depended on the initial Salmonella spp. contamination level. A sample contaminated at 1 CFU/g was called positive by the GeneDisc method after 2 h of enrichment while detection of a sample contaminated by as low as 1 CFU/sample required to be enriched for 5 h.

Significance: Beef meat processors can now sort their incoming meat to a specific process based on an informed decision about contamination. This generates an increased profitability by reducing end-product scrap.