The objective of this project was to evaluate the use of the Premi®Test Salmonella (PTS) system as a serotyping tool to identify pork and poultry isolates obtained from vertically integrated operations and to compare the performance of the PTS system with traditional Kauffman-White (KW) serotyping methods.
Identification of serotypes from the USDA culture collection using the PTS system was reproducible independently of the source (pork or chicken) or replication. Serotypes (69%) present in the PTS database were successfully indentified as Salmonella and matched traditional serotyping. Isolates (31%) were identified as Salmonella, but did not match the results from traditional serotyping. Further investigation indicated that these discrepancies may be due to mistyping of the original isolates by the traditional method or overlaps with known serotypes. Isolates not present in the PTS database were recognized as Salmonella genovars, although the profile was unknown.
Serotyping of the fresh isolates yielded some interesting information. Both methods correctly identified the species as Salmonella 100% of the time. Two serotypes, S. Ohio and S. Anatum, comprised over 50% of the total number of isolates found in pork; while S. Kentucky and S. Braenderup made up over 80% of the isolates found in chicken. When the PTS system can not identify a serotype, many times it will assign a genovar number to the sample. A genovar score is a unique number assigned to a microarray pattern based on the combination of positive and negative hybridization reactions. While it may or may not accompany a serotype, this number can be used to compare isolates in a broad sense to determine whether they are comparable. Contaminations could be tracked using the genovar score even if the serotype is unknown. Further typing by KW could be used as a follow up method if a greater level of sensitivity is required.
The results from this study indicate that the PTS system is a robust tool that can bring rapid, routine serotyping analysis to more laboratories. Currently, few laboratories conduct routine serotyping due to the cost of purchasing and storing numerous types of antisera, which have a very short shelf life. In addition, many laboratories do not have the expertise or training needed to perform this technique. The PTS system requires only that a technician have sufficient microbiological and pipetting skills to perform the analysis. Even if a serotype is not reported, the genovar score allows another level of discrimination that would be useful for tracking Salmonella in pork and poultry operations.