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

Use of flow cytometry to rapidly detect Salmonella in chicken carcass washe s was investigated. A direct immunomagnetic separation method was used to p repare samples and was found to be an effective method for separating targe t cells from debris in chicken carcass washes. When flow cytometry was comb ined with immunomagnetic separation, the average lowest detectable level of Salmonella detected was 2.3 x 10(4) CFC/ml. Fifty of 100 wash samples from six groups were inoculated with 2 x 10(-1) CFU of Salmonella Typhimurium p er milliliter. After 18 h of enrichment at 37 degrees C, all samples were t ested 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 si gnificant linear relationship between the enumeration results of flow cytom etry and xylose-lysine-tergitol agar plate counts (R-2 = 0.796). Time requi red for flow cytometry, including sample processing and flow cytometric ana lysis, was less than 1 h.