Detection of Salmonella enteritidis in incubated pools of egg contents by fluorescence polarization and lateral flow immunodiffusion

United States Department of Agriculture, Agricultural Research Service, Southeast Poultry Research Laboratory, 934 College Station Road, Athens, Georgia 30605, USA. rgast@seprl.usda.gov

Efficient detection of Salmonella enteritidis inside eggs is critical for confirming that individual commercial laying flocks present a risk to public health. In most standard bacteriological culturing protocols, an initial incubation step is necessary to allow the typically very small population of S. enteritidis cells in pools of egg contents to multiply to more easily detectable levels. In the present study, two rapid methods were evaluated as alternatives to plating on selective media for detecting S. enteritidis in incubated egg pools. By using either fluorescence polarization or lateral flow immunodiffusion assays, S. enteritidis could be consistently detected in egg pools at 10(8) cfu/mL (and in most pools at 10(7) cfu/mL). Although the rapid assays were significantly less sensitive than culturing, they both were consistently able to detect contamination when pools of 10 eggs were inoculated with approximately 10 cfu of S. enteritidis and incubated for 72 h at 25 degrees C.