Antibody responses in the serum and gut of chicken lines differing in cecal carriage of Salmonella enteritidis.

Salmonella frequently causes human foodborne infections. Contaminated products from poultry infected with Salmonella enteritidis are mainly involved. This serovar is able to colonize the gastrointestinal tract and generally produces a chronic asymptomatic carrier state in poultry, except in very young birds. We have developed a model of S. enteritidis carriage in chicks and found that four chicken lines, B13, L2, PA12 and Y11 differ in their cecal colonization by S. enteritidis, whereas their systemic organs are similarly infected. We have monitored the serum and gut antibody responses of these four lines to S. enteritidis for 9 weeks post inoculation (pi). We confirm that S. enteritidis infected the spleens of the four chicken lines similarly, and that it often colonized the ceca at levels significantly higher in B13 and L2 chicks than those of the PA12 and Y11 chicks. The serum IgM and IgG antibody responses were high and the serum IgA antibody responses low. In contrast, the intestinal secretions contained mostly IgA antibodies. The serum IgM antibody values of the four chicken lines were similar. However, the B13 and L2 chicks often had significantly higher serum IgG and IgA antibody responses than PA12 and Y11 chicks. Only the B13 and L2 chicks showed high, persistent levels of IgA antibody in intestinal secretions. These results suggest that most antibody responses are related to cecal colonization by S. enteritidis. They also indicate that factors other than the antibody levels are involved in the control of this colonization.

Reliable ELISAs showing differences between resistant and susceptible lines in hens orally inoculated with Salmonella Enteritidis.

Reliable ELISAs were investigated with the aim to select hen lines resistant to Salmonella Enteritidis and producing high levels of antibodies. In the first experiment, the relation between the humoral response and the bacteriological results was assessed on hens from the Y11 resistant line and the L2 susceptible line, orally inoculated with 10(8) CFU S. Enteritidis per animal. Anti-lipopolysaccharide (LPS) IgG titres were higher but the liver and spleen were less contaminated in hens from the Y11 line than in hens from the L2 line (p = 0.013, 0.031 and 0.026 respectively). In the second experiment, the hens were inoculated orally with 1.7 x 10(8) CFU S. Enteritidis per animal in order to select the ELISA methods showing the more significant differences. ELISAs were based on LPS, flagella, LPS from rough (LPS-R) and smooth strains (LPS-S) and detected IgG and IgM antibodies from sera and yolks. No between-line host response variation was observed in the yolk, with LPS-S and R antigens nor with anti-LPS IgM in the sera. Otherwise, significant differences were encountered between hen lines with the ELISAs performed on the sera detecting anti-LPS IgG, anti-flagella IgG or IgM (p = 0.017, 0.017 and p < 0.001 respectively). When comparing the kinetics of the selected ELISAs, the IgG antibodies against LPS detected between-line variations as early as 1 to 4 weeks pi, whereas with IgG against flagella, the differences were only detected at 1 and 2 weeks pi and with IgM against flagella, the differences were significant at 1, 2, 4 and 8 weeks pi. In conclusion, resistant hen lines producing higher levels of antibodies than the susceptible hen lines may be selected with these ELISAs.