A 7-plex microbead-based immunoassay for serotyping Shiga toxin-producing Escherichia coli.

Serotyping of Shiga toxin-producing Escherichia coli (STEC) has been contingent upon the availability of antisera. Here we describe a 7-plex microbead-based immunoassay to simultaneously serotype seven STECs (i.e., belonging to serogroups O26, O45, O103, O111, O121, O145, and O157) by the Luminex xMAP® technology. This technology presents many advantages: Its multiplexed format (up to 100 analytes) saves time, reagents, and test sample, and many regulatory agencies currently utilize this platform for other assays. In this study, a total of seventy-nine STEC strains belonging to the 7 different serogroups of interest were tested. These strains had been previously serotyped and their serogroup was confirmed by PCR. Except for one strain belonging to the O111 serogroup, nearly all strains (i.e., 98.7%; 78/79) were correctly identified on the Bio-Plex 100 instrument in less than 4h. This newly developed microbead-based immunoassay could be extended to include other STEC serogroups, virulence factors, and/or bacterial species.