Development and Application of an Enzyme-Linked Immunosorbent Assay to Detect Antibodies against Prevalent Salmonella Serovars in Swine in Southern Brazil

Abstract

The implementation of Salmonella control programs in the pork production chain demands rapid and cost-effective methods to assess the prevalence of infection in pig herds. The objective of the present study was to develop an in-house enzyme-linked immunosorbent assay (ELISA) based on S. Typhimurium lipopolysaccharides (LPS) to measure the prevalence of infection caused by Salmonella in swine herds. Coating antigen was produced by phenol extraction of S. Typhimurium culture. After standardization of ELISA test conditions, the assay was validated by testing serum samples on different animal categories: pigs orally inoculated with S. Typhimurium and sentinel animals in contact with them, naturally infected animals, colostrum-deprived piglets, and bacterin-immunized pigs. Seroconversion was observed in inoculated pigs (7 days postinfection [DPI]) and in the sentinels (21 DPI). Nonspecific reactions were not detected in the sera of colostrum-deprived animals. Serum samples from animals immunized with Salmonella Agona, Salmonella Derby, Salmonella Panama, and Salmonella Bredeney bacterins showed marked cross-reaction with the LPS from the serovar Typhimurium. Moreover, positive results obtained with the in-house ELISA were associated with Salmonella isolation in 75 infected pig herds. Comparisons with 2 commercial kits showed a linear correlation coefficient of 0.847 between the in-house ELISA and kit A and 0.922 with kit B but a low agreement in the qualitative results. In conclusion, the newly developed in-house ELISA based on S. Typhimurium LPS can be a useful tool to determine the intensity of Salmonella sp. infection in swine herds.