Growth of Salmonella enteritidis in Yolk of Shell Eggs from Normal and Seropositive Hens

The growth of Salmonella enteritidis inoculated into the yolks of shell eggs from normal and seropositive hens was determined at various temperatures. All eggs were inoculated with approximately 1 colony-forming unit (CFU)/g of yolk. In eggs from normal hens, the organism multiplied with a generation time of 25 min, reaching a density of about 10⁸ CFU/g in 12 h at 37°C. A generation time of 3.5 h was observed in eggs incubated at 15.5°C, a temperature frequently used for commercial storage of eggs. Cell density of >10⁷ CFU/g was reached in 4 d at 15.5°C. No multiplication was observed in eggs incubated at 7°C for 94 d. When inoculated eggs from seropositive birds were incubated at 37°C, the organism multiplied with a generation time of 35 min, reaching a cell density of >10⁶ CFU/g in 12 h. Raw egg white was detrimental to cells, reducing cell viability 50% in 4 h at 37°C. The limulus amoebocyte lysate test gave a positive reaction with whole liquid egg containing <10³ CFU/g. A protocol is suggested for possible application of this test in epidemiological studies that screen grade A shell eggs for Salmonella contamination.