Improvements to a PCR-Based Serogrouping Scheme for Salmonella enterica from Dairy Farm Samples

Molecular serotyping through the use of PCR is a simple and useful technique for characterizing isolates of Salmonella enterica subsp. enterica belonging to serogroups B, C1 , C2, D1, and El, which are the majority of the isolates associated with human disease outbreaks. However, many of the Salmonella strains currently isolated from dairy farms in the northeastern United States are serovar Cello, a group K strain not detected by this assay. Primers from a well-known PCR assay for the identification of Salmonella were added to a commonly used serotyping assay so that strains, such as Salmonella Cerro, that do not produce bands in the original assay can be confirmed as belonging to S. enterica subsp. enterica. The modified assay frequently misidentified the serogroup of Salmonella Mbandaka isolates because of failure to amplify the wzxC1 amplicon. Therefore, the reverse primer for the wzxC1 target was modified based on in silico analysis to provide consistent classification of Salmonella Mbandaka as belonging to serogroup C1. These two modifications to the serogrouping PCR method enhance the utility of the method for characterizing Salmonella isolates.