Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2015
Publication Date: 6/1/2015
Citation: Karns, J.S., Haley, B.J., Van Kessel, J.S. 2015. Improvements to a PCR-based serogrouping scheme for Salmonella enterica from dairy farm samples. Journal of Food Protection. 78:1182-1185.
Interpretive Summary: Salmonella is an important foodborne pathogen and it is often found in dairy cattle and their environments. Because there are many different types of Salmonella, isolates obtained from animals and their environment need to be further characterized in order to study the ecology of this pathogen. One way to characterize isolates is to group them into serogroups. We were using a PCR (polymerase chain reaction) assay developed by other researchers to place our isolates into serogroups but the assay wasn’t able to characterize many of the dairy related isolates. We made two changes to the method that resulted in an assay that can be used for confirming that the dairy farm isolates were Salmonella and for categorizing the Salmonella into serogroups. The new assay enhances the utility of the method for characterizing isolates from U.S. dairy farms. This information will be useful to other scientists and regulatory agencies.
Technical Abstract: The PCR method described by Herrera-León, et al. (Research in Microbiology 158:122-127, 2007) has proved to be a simple and useful technique for characterizing isolates of Salmonella enterica enterica belonging to serogroups B, C1, C2, D1, and E1, groups which encompass a majority of the isolates from human disease outbreaks. However, many of the Salmonella currently isolated from dairy farms in the Northeastern U. S. are serotype Cerro, a Group K strain not detected by this assay. Primers from a well known PCR assay for the identification of Salmonella were added to the assay of Herrera-León, et al. so strains, such as S. Cerro, that do not produce bands in the original assay are confirmed as belonging to Salmonella enterica enterica. The modified assay was found to frequently misidentify the serogroup of serotype Mbandaka isolates because of failure to amplify the wzxC1 amplicon. Therefore, the reverse primer for the wzxC1 target was modified based upon in silico analysis to provide consistent classification of serotype Mbandaka as belonging to serogroup C1. These two modifications to the serogrouping PCR method enhance the utility of the method for characterizing isolates from U.S. dairy farms.