Quantitative Method for Detecting Salmonella Species Using the Bio-Theta DOX^TM System

Abstract

　We developed a method for quantitatively detecting non-typhoidal Salmonella (NTS) in food using the DOX^TM system. The system was able to detect low concentrations (approximately 1 log CFU/mℓ) of ten strains of NTS, and could not detect moderate concentrations (approximately 3 log CFU/mℓ) of 32 strains belonging to 26 non-Salmonella species examined in this study. The detection time and bacterial count for the ten NTS serotypes had a good, linear calibration curve (correlation coefficient (r) was ＞0.93). We carried out a recovery examination by inoculating samples of 5 meats with S. Enteritidis, Infantis, and Typhimurium, and each sample was examined five times. Total of 150 examinations as all 5 meats inoculated with a medium concentration (2 to 3 log CFU/mℓ) and low concentration (1 to 2 log CFU/mℓ) of the 3 NTS serotypes showed positive. Each three serotypes were detected in 24 of the 25 examinations inoculated with an ultra-low concentration of bacteria (＜1 log CFU/mℓ), and the detection time for positive samples was 680～988 min. The average detection time of S. Enteritidis, Infantis, and Typhimurium were 772 min, 753 min and 787 min, respectively. The DOX system may be a useful tool for establishing the presence of NTS at levels of more than 250 CFU/25 g in food and environmental samples at food processing companies. However, additional validation studies comparing the DOX system and other available official methods are needed.