Comparison of Direct Culture, Immunomagnetic Separation/culture, and Multiplex PCR Methods for Detection of Salmonella in Food

In this study, an optimized method was developed to detect Salmonella by using immunomagnetic separation coupled with culture to selective agar (IMS/culture). To test the effectiveness of the methods and develop a rapid and sensitive detection procedure, direct culture, IMS/culture, and multiplex PCR (mPCR) were compared for the detection of Salmonella in 700 food samples. After selective enrichment, all samples were (I) subjected to direct culture, plated on xylose-lysine-tergitol 4 agar, and identified as Salmonella via biochemical and serological methods; (II) subjected to IMS then identified as (I); and (III) subjected to DNA extraction and mPCR analysis. A total of 83, 95, and 104 samples were found positive for Salmonella by direct culture, IMS/culture, and mPCR, respectively. Results suggested higher sensitivity in mPCR than in direct culture and IMS/culture methods. IMS/culture increased the detection rate of Salmonella and compared well with mPCR. This study demonstrated that the use of mPCR in pre-screening of samples and further identification by IMS/culture should enhance the positive identification and increase the number of isolates of Salmonella.