Multiplex, bead-based suspension array for molecular determination of common Salmonella serogroups.

We report the development and evaluation of a Salmonella O-group-specific Bio-Plex assay to detect the six most common serogroups in the United States (B, C(1), C(2), D, E, and O13) plus serotype Paratyphi A. The assay is based on rfb gene targets directly involved in O-antigen biosynthesis; it can be completed 45 min post-PCR amplification. The assay correctly and specifically identified 362 of 384 (94.3%) isolates tested in comparison to traditional serotyping. Seventeen isolates (4.4%) produced results consistent with what is known about the molecular basis for serotypes but different from the results of traditional serotyping, and five isolates (1.3%) generated false-negative results. Molecular determination of the serogroup for rough isolates was consistent with a common serotype in most instances, indicating that this approach has the potential to provide O-group information for isolates that do not express an O antigen. We also report the sequence of the O-antigen-encoding rfb gene cluster from Salmonella enterica serotype Poona (serogroup O13). Compared with other, previously characterized rfb regions, the O13 rfb gene cluster was most closely related to Escherichia coli O127 and O86. The O-group Bio-Plex assay described here provides an easy-to-use, high-throughput system for rapid detection of common Salmonella serogroups.