Abstract: A method for the selective detection of viable cells of Salmonella in meat and meat products was developed using propidium monoazide (PMA) staining in combination with conventional PCR (PMA-PCR). Exposure time and PMA concentration were optimized to find optimal PMA-based PCR conditions for distinguishing between dead and viable cells. The results showed that the optimal light exposure time to activate PMA in dead cells and to photolyze free PMA in solution was 15 min. PMA at a dose of 10 μg/mL or less could not inhibit PCR amplification of DNA derived from viable cells of Salmonella. The minimum concentration of PMA to completely inhibit PCR amplification of DNA derived from heat-killed cells was 4 μg/mL. After PMA treatment, viable Salmonella cells in a mixture containing different proportions of viable and dead cells could be selectively detected by PCR, and the minimum detection level was 20 CFU/PCR. An excellent linear relationship was observed between relative fluorescent intensity of DNA bands and lgCFU in the range of 20－2 × 105 CFU/PCR. Among 30 meat and meat product samples, two samples were detected by the developed PMA-PCR method as being positive after 6 h enrichment with average amounts of 2.5 × 103 CFU/mL and 3.4 × 103 CFU/mL for viable Salmonella cells, respectively.

Key words: meat and meat products, Salmonella, viable cells, propidium monoazide-based polymerase chain reaction (PMA-based PCR)