The growth study of Salmonella enterica serovar Enteritidis inoculated in different sites of eggs and various incubation conditions

This research was conducted to determine the effects of temperature, the inoculation site and storage time on growth and survival of Salmonella enterica serovar Enteritidis in whole eggs. For this purpose, 108 fresh eggs were collected from a layer farm. In a factorial design, egg shell, air cell, albumen and the vicinity of yolk were inoculated with 550 bacterial cells. The inoculated eggs were incubated for 7, 21 and 42 days at 7, 25 and 37°C. To determine bacterial growth, colony counting method was used. The results showed that 500 bacterial cells were unable to penetrate in intact egg shells. Also, there was no bacterial growth at 7°C. In other experimental groups, the bacterial growth was determined as follows. In the air cell, bacterial growth was determined only after 42 days of incubation at 25°C. In the albumen, there was no bacterial growth after 7 and 21 days of incubation at 25°C. In the vicinity of yolk, bacterial growth was determined in all of the experimental groups except at 7°C. In each treatment, that bacterial growth was observed; their number was above 8.2 log CFU/ml of egg content. By statistical analysis of Salmonella cell number in the albumen and the vicinity of yolk, significant changes (P<0.05) in bacterial count were observed, based on increasing of storage time and incubation temperature. Research findings indicated that the site of bacterial contamination and temperature and the duration of storage have highly significant effects on the growth of Salmonella in egg content.