Intrinsic and extrinsic factors influencing eggshell penetration by Salmonella: W. Messens et al. XI

To prevent penetration of Salmonella into eggs, a clear understanding of various factors influencing bacterial penetration could be a valuable tool in planning intervention strategies. Penetration was assessed by replacing the egg contents with a selective medium that allowed visualising Salmonella growth on the inside of the shell by candling. Only eggshells without visual abnormalities were used. Eggs from one ISA-Brown Warren laying flock were used to determine the effect of hen age and storage conditions. A faster appearance of penetration spots was observed with increasing storage temperatures possibly caused by increased growth rates of SE on the agar. Although shell characteristics differed with hen age, hen age did not influence SE penetration. Eggshell penetration varied greatly between eggs bought at a warehouse. Only 6% of the eggs from “free range” hens and 16% of the “white” eggs were contaminated. The remaining eggs (bio, columbus and brown) were contaminated at a frequency of ca 33%. Eggs from both ISA-Brown Warren and Bovan Goldline hens kept in 2 types of housing system (furnished cage versus aviary) and fed 2 types of feed (standard feed versus feed containing corn cob mix) were tested. The breed of the hen neither the housing system did affect the eggshell penetration by SE. Eggs from hens fed CCM were more frequently penetrated. Hence, the feed can play an important role to reduce eggshell penetration. No correlations were observed between any of the shell characteristics studied and the ability of SE to penetrate the shell, although the egg(shell) characteristics of the various eggs differed greatly. One factor that is of major significance is the growth of SE on the shell because shell contamination at the end of storage and SE penetration were highly correlated. Thus, SE growth on the shell should be prevented.