Abstract: Objective　To evaluate specific enrichment reactions of immunomagnetic beads of Shigella, and to provide the technical basis for establishing immunomagnetic separation method for the detection of Shigella species. Methods　Pure cultures of Shigella species(except Shigella boydii) and nontarget bacteria (Escherichia coli， Enterobacter aerogenes， Acinetobacter baumannii， Klebsiella pneumoniae， Vibrio fluvialis and Staphylococcus epidermidis) were used to calculate specific and nonspecific capture efficiencies of the immunomagnetic beads by counting the colony. Interference experiments were designed to evaluated the specific enrichment reaction of the immunomagnetic beads, which was performed by adding the immunomagnetic beads into the suspensions of the mixtures with 104 cfu/mL Escherichia coli and different concentrations of target bacteria. The beads were used to capture the Shigella from the milk powder samples which were preenriched for 3 and 6 h and fecal samples. The possibility of using immunomagnetic separation method to detect Shigella was evaluated. Results　The capture efficiency of immunomagnetic beads was above 30% to the pure cultures of Shigella dysenteriae， Shigella flexneri and Shigella sonnei, and the nonspecific capture efficiency of 6 nontarget bacteria was below 3%. The data of the interference experiments showed that immunomagnetic separation method had 100 fold increasing in the detection sensitivity in comparison with conventional testing methods. The results of the tests of artificially inoculated milk powder and fecal samples showed that the detection limits could reach 101 cfu/25g and 101 cfu/mL by immunomagnetic separation method, and the detection rate of the target bacteria increased. Conclusions　Immunomagnetic beads have some specific capture and enrichment reactions to Shigella dysenteriae, Shigella flexneri and Shigella sonnei, and it should be applied into routine diagnostic determinations.

Key words: Immunomagnetic bead, Shigella, Capture efficiency