Serologic detection of experimental salmonella enteritidis infections in laying hens by fluorescence polarization and enzyme immunoassay

Detection of infected poultry flocks is essential for controlling eggborne transmission of Salmonella enteritidis to humans. The present study evaluated the detection of antibodies in the sera of experimentally infected chickens by a fluorescence polarization assay with a tracer prepared from the O-polysaccharide of S. enteritidis and an enzyme-linked immunosorbent assay (ELISA) with an S. enteritidis flagellin antigen. In two trials, groups of specific-pathogen-free laying hens were infected orally with either 101 or 101 colony-forming units (CFU) of. enteritidis (phage type 13a) or with 10(8) CFU of Salmonella typhimurium. Serum samples were collected before inoculation and at five subsequent weekly intervals. Both assays successfully detected the majority of hens infected with S. enteritidis at either dose level, but they also identified a substantial number of hens infected with S. typhimurium as seropositive. The fluorescence polarization test detected S. enteritidis infection significantly more often and cross-reacted with sera from hens infected with S. typhimurium significantly less often than the ELISA. The fluorescence polarization assay also offered advantages in terms of speed and methodologic simplicity.