Rapid detection of Salmonella in chicken washes by immunomagnetic separation and flow cytometry

Use of flow cytometry to rapidly detect Salmonella in chicken carcass washes was investigated. A direct immunomagnetic separation method was used to prepare samples and was found to be an effective method for separating target cells from debris in chicken carcass washes. When flow cytometry was combined with immunomagnetic separation, the average lowest detectable level of Salmonella detected was 2.3 x 10(4) CFU/ml. Fifty of 100 wash samples from six groups were inoculated with 2 x 10(-1) CFU of Salmonella Typhimurium per milliliter. After 18 h of enrichment at 37 degrees C, all samples were tested for Salmonella using flow cytometry and conventional culture methods. An identification correlation of 96% was found between flow cytometry and xylose-lysine-tergitol agar plating. Quantitative analysis established a significant linear relationship between the enumeration results of flow cytometry and xylose-lysine-tergitol agar plate counts (R2 = 0.796). Time required for flow cytometry, including sample processing and flow cytometric analysis, was less than 1 h.