Quantitative method for detecting Staphylococcus aureus using Bio-Theta DOXTM system

Abstract

We developed a novel quantitative method for detecting S. aureus using the DOXTM system. A total of 19 strains of S. aureus, and 36 strains of non-S. aureus containing 27 species were examined. The mean positive rate of the high- (103 CFU/ml), medium- (102 CFU/ml), and low-concentration (10 CFU/ml) S. aureus samples was all 100%. The relationship between detection time and bacterial count of the 19 S. aureus had a good linear calibration curve. For the 36 non-S. aureus samples, the mean negative rates for the high-concentration (106 CFU/ml) samples and the medium-concentration (103 CFU/ml) samples were both 94.4% (34/36). The 2 positive non-S. aureus samples were S. xylosus ATCC 29971 and Enterococcus faecalis ATCC 29212. Furthermore, a recovery examination was carried out by inoculating 20 food samples with S. aureus isolated from rice ball and each sample was examined 2 times. S. aureus was detected in all samples inoculated with a low concentration of the organism (1.30-1.37 log CFU/ml), and the detection time of the positive samples was 477-807 min (9.7 hrs on average). The DOX system provided rapid results (usually within 10 hrs) and required no special techniques for measurement. Therefore, the DOX system may be a useful tool for determining the absence of S. aureus in food and environmental samples at food processing companies. However, more validation studies and field studies are needed.