INFECTION AND REINFECTION OF CHICKENS WITH SALMONELLA-TYPHIMURIUM - BACTERIOLOGY AND IMMUNE-RESPONSES

Four-day-old chickens infected orally with a spectinomycin-resistant (Spc(r)) mutant of a highly invasive avian Salmonella typhimurium strain excreted salmonellae in the feces for at least 10 weeks. When these chickens were reinfected at this time with a nalidixic acid-resistant (Nal(r)) mutant of the same strain, they excreted this mutant in significantly smaller numbers (P < 0.01) than did a previously uninfected control group. The Nal(r) mutant had a shorter survival rate in the tissues of the immunized chickens than in tissues of the control birds. The Spc(r) mutant stimulated strong IgG, IgA, and IgM responses in serum, small-intestinal contents, and bile. These were detected by enzyme-linked immunosorbent assay (ELISA) against antigens of crude whole bacterial cell protein sonicate, lipopolysaccharide, flagella, and outer-membrane proteins. There was some evidence of an anamnestic response with IgA in bile following reinfection with the Salmonella. The peak response of antibody-producing cells from the spleens of infected chickens, assayed by solid-phase ELISA, occurred at 3 weeks postinoculation. A strong delayed hypersensitivity reaction, detected by foot-pad swelling after inoculation with either whole-cell or outer-membrane proteins, was observed between 2 and 5 weeks after infection with the Spc(r) mutant. The data indicate that outer-membrane proteins are major immunogens for both humoral and cell-mediated arms of the immune system.