Detection of Salmonella Infection in Chickens by an Indirect Enzyme-Linked Immunosorbent Assay Based on Presence of PagC Antibodies in Sera

The outcomes of infection of humans and animals with Salmonella range from a persistent asymptomatic carrier state to temporal mild gastroenteritis or severe systemic infection. A rapid and accurate diagnostic test would help formulate strategies for effective prevention of their infections in the animal population. Current sequencing data predict that the outer membrane protein, PagC, is present in all common Salmonella serovars with sequence similarities of more than 98%. PagC sequences in other bacterial species are less than 65% similarity at the amino acid level to those of Salmonella PagC. We hypothesized that PagC could be immunogenic and detection of antibodies to this protein could be an accurate indicator of Salmonella infection. The pagC gene from Salmonella enterica serovar Typhimurium CVCC542 was expressed in Escherichia coli. The purified recombinant PagC protein was immobilized in microtiter plate wells. Sera from SPF chickens infected with Salmonella or other non-Salmonella pathogens by injection were added and binding of PagC protein was detected by the horseradish peroxidase (HRP)-labeled goat anti-chicken antibody. Sera from Salmonella-infected chickens showed high specificity in contrast to the sera from chickens infected with other bacteria. When 87 Salmonella antibody-positive sera from Salmonella Pullorum orally infected SPF chicken and 93 negative sera from uninfected SPF chicken were tested, 98.3% agreement was detected. The rPagC enzyme-linked immunosorbent assay (ELISA) and agglutination had 80.6% agreement in detecting 252 clinical chicken sera samples. These results suggest that PagC antibody-based indirect ELISA can serve as a convenient and novel method for the diagnosis of Salmonella infection.