Estimation of Viable Salmonella Cell Numbers in Meat and Meat Product Using Real-Time PCR

Abstract

Recently we developed a novel method for estimating viable Salmonella cell numbers by means of a 5῎-nuclease real-time PCR [Fujikawa et al., J. Food Hyg. Japan, 47, 151ῌ156 (2006)]. The method was based on the increase kinetics of the target DNA region (inv A) of the microorganism growing in a culture medium during incubation. The index for the PCR was the threshold cycle. In this study, we validated the method for application in food. Namely, Salmonella cells spiked into ground chicken, pork, and beef and raw hamburger patty at various cell concentrations were cleaned up using buoyant density centrifugation and the Salmonella cell numbers were estimated with our method. Linear decreases in the threshold cycle value were observed during incubation of the samples. The standard curves for the cell number in all food samples were almost identical. With a standard curve using the mean parameter values, we successfully estimated viable Salmonella cell concentrations of the foods. The results indicate that our method is applicable for viable cell number estimation of the target microorganism in foods. Further, we used this method to study Salmonella growth in ground chicken stored at a constant temperature.

Prevalence, Numbers and Antimicrobial Susceptibilities of Salmonella Serovars and Campylobacter spp. in Retail Poultry in Phnom Penh, Cambodia

“…The numbers of Salmonella in our study varied from less than 1 to 4 log 10 CFU/g for 134 samples. Nevertheless, no spoilage was observed in the poultry meat before processing and it was thought that competition among the micro-organisms in the poultry meat might suppress the growth of Salmonella cells [8]. A previous study showed that inoculated 10 5 CFU/g of Salmonella cells in minced meat, they grew to a high population level (10 9 CFU/g) [13].…”

Rapid detection of viable Listeria monocytogenes in chilled pork by real-time reverse-transcriptase PCR

“…Recently studies have been carried out to determine the suitability of using RNA to quantify pathogens by real-time reversetranscriptase PCR (real-time RT-PCR) (McCabe et al, 2011a(McCabe et al, , 2011bMiller, Davidson, & D'Souza, 2011, Miller, Draughon, & D'Souza, 2010. However most of these methods required one-or two-step enrichments prior to real-time RT-PCR in order to detect a small number of target cells (Fujikawa & Shimojima, 2008). Until now, rapid detection of viable L. monocytogenes without enrichments in chilled pork by real-time RT-PCR has not been reported.…”