Serological response of chickens naturally infected with Salmonella typhimurium detected by ELISA

Serological distinction of bovine Salmonella carriers from vaccinated and acutely infected cows

Identification of Salmonella carriers using lipopolysaccharide (LPS) ELISA serology in a Salmonella-infected herd requires distinction of chronically infected cattle from convalescent and vaccinated cows. Cows responding to Salmonella infection and vaccination produce titers to Salmonella LPS that overlap with the lower titers of some Salmonella carriers. The objective of this study was to determine if the LPS antigen specificity of the bovine humoral immune response to Salmonella LPS antigens differs following vaccination and acute and chronic Salmonella infection. The study focused on the nondiscriminatory area of Salmonella ELISA serology, specifically, peak-titered sera from Salmonella bacterin-vaccinated and experimentally infected cows and low-titered sera from Salmonella carriers. The LPS serogroup specificity of the IgG1 and IgG2 response following acute and chronic Salmonella serotype Dublin infection and Salmonella bacterin vaccination was evaluated using 5 Salmonella serogroup (B, D, E1, C3, and C1) LPS ELISA assays. IgG, titers of carriers, vaccinated, and acutely infected cows were predominantly O antigen specific. Similarly, the IgG2 titers of acutely infected cows were also O antigen specific. In contrast, Salmonella carriers produced an IgG2 response to each of the heterologous LPS antigens (B, E1, C3, and C1) examined. The results of this study indicate that the bovine IgG1 isotype response to Salmonella LPS is serogroup specific. Conversely, production of IgG2 antibodies to core Salmonella LPS antigens shared across Salmonella serogroups is a feature of chronic Salmonella infections.

The humoral and cell mediated immune response of young chicks to Salmonella typhimurium and S. Kedougou

Day old chicks were inoculated with either Salmonella typhimurium or S. Kedougou as representative examples of an invasive and a non-invasive strain respectively. The titres of IgA, IgG and IgM antibodies were determined, using an enzyme-linked immunosorbent assay (ELISA) in the bile, serum and homogenates of intestinal mucosa each week up to 5 weeks of age. Statistically significant increases in antibodies were detected in the bile (IgA and IgG) and the intestinal mucosa and serum (IgG and IgM) 1 week after the birds were inoculated with S. typhimurium. In contrast, only a limited response was recorded for S. kedougou 4 weeks after challenge commenced. The birds appeared capable of eliminating systemic infection with S. typhimurium as they grew older although a cell mediated immune response was demonstrated in less than half the birds aged 4 or 5 weeks. The demonstration of only a limited serological response to S. kedougou indicates that serological testing may have a limited role in monitoring flocks for infection with non-invasive serotypes.