Evaluation of a Bead-based Molecular Serotyping Tool for Salmonella

Introduction: The Kauffman-White (KW) classification scheme is the standard for determining > 2,500 Salmonella serotypes through the use of antisera, however, reagent lot variability, quality, and shortages limit this method. Molecular serotyping addresses these limitations. One method, developed by the CDC, is the Salmonella Serotyping Assay (SSA) which utilizes xMap technology from Luminex. Luminex microspheres are coated with reagents specific to particular DNA biomarkers and are used to capture analytes. Three separate PCR assays: O-group Assay (8 targets), H-group Assay (35 targets) and Additional Target Assay (3 targets) are multiplexed, which allows for the simultaneous amplification of two or more targets in one PCR tube. The dye-labeled amplification product is detected on the Luminex analyzer and converted to digital data. The technician classifies and interprets the data to determine serotype based on the KW scheme.

Purpose: The purpose of this work was to assess SSA from Luminex as a Salmonella serotype identification tool in comparison to traditional serotyping using antisera.

Methods: One hundred twenty-four Salmonella isolates were used in this study. All samples were prepared for analysis following the manufacturer’s protocol and screened with the Luminex assay. Data was analyzed and entered into the Luminex software tool to determine the serotype or candidate serotypes. The identities of these isolates were also determined by traditional serotyping.

Results: SSA results agreed with the antisera result for 60 isolates (48%). An additional 51 isolates (41%) were partially matched but required further analysis of single factors (due in part to several factors not being included in assay). Thirteen isolates (11%) results did not match antisera result.

Significance: The SSA can fully serotype 80 of the top 100 clinically-associated serotypes. However, SSA capability of partial serotyping, thus lowering the number of agglutination assays required to determine identity, could make it an option for molecular-based serotyping of Salmonella.