Quantitative Method for Detecting Listeria Species using the Bio-Theta DOXTM System

Abstract

We developed a quantitative method for detecting Listeria species in food using the DOXTM system. The system could detect low concentrations (10 cfu/ml) of Listeria monocytogenes, L. innocua, and L. welshimeri, and could not detect medium concentrations (103 cfu/ml) of the 29 non-Listeria organisms examined in this study. The relationship between detection time and bacterial count of the 3 Listeria species had a good linear calibration curve. We carried out a recovery examination by inoculating 15 food samples with L. monocytogenes, and each sample was examined 5 times. L. monocytogenes was detected in 68 of the 75 samples inoculated with an ultra-low concentration of bacteria (<1 log cfu/ml), and the detection time of the positive samples was 1,052–1,870 min (average, 21.9 h). The DOX system provides rapid results (usually within 1 day), and requires no special techniques for measurement. The DOX system may be a useful tool for determining the presence of Listeria spp. in food and environmental samples at food processing companies, though more validation studies and field studies are needed.