Eggshell penetration by 'Salmonella' Typhimurium in table eggs: Examination of underlying eggshell structures by micr-computed tomography and scanning electron microscopy

Horizontal infection of table eggs by food borne, human infection causative agents such as 'Salmonella' is a serious concern for consumers and industry. In this study, we investigated the relationship between eggshell translucency, mammillary layer abnormalities and pore structure using Computed Tomography (CT) and scanning electron microscopy. The effects of eggshell pore structure, size and number on 'Salmonella' Typhimurium penetration was also investigated. The eggs were infected with S. Typhimurium and were incubated at 37 °C for 3 or 6 days. Micro CT results comparing shell features to shell translucency found that there was a significantly increased incidence of externally branching pores found in the high translucency score eggshell group, and more straight pores found in the low translucency score group. Different pore structures, the total number of pores and the shell thickness do not appear to play a role in the horizontal infection of eggs by the S. Typhimurium strain used in this study. While it is likely that the presence of shell pores is responsible for shell penetration, other unknown shell factors must also play a role, and eggshells with a higher incidence of shell pores are not penetrated at a higher rate.