A comparative study on the pathogenesis of egg contamination by different serotypes ofSalmonella

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Abstract
Salmonella enterica serotype Enteritidis is the predominant serotype associated with egg-borne salmonellosis in humans. Apparently this serotype possesses particular characteristics that increase its chance to contaminate eggs. To identify these characteristics, two Salmonella serotype Enteritidis strains as well as one strain of each of the serotypes Salmonella Typhimurium, Salmonella Heidelberg, Salmonella Virchow and Salmonella Hadar strain were used to examine different aspects related to egg contamination. After an intravenous infection of laying hens, it was observed that the ability of the serotype Enteritidis strains to colonize the reproductive organs was significantly higher compared with the Salmonella Heidelberg, Salmonella Virchow and Salmonella Hadar strains but not with the Salmonella Typhimurium strain. Inoculating low numbers of the different Salmonella serotypes in egg albumen at 42°C demonstrated that the growth of the strains belonging to the Salmonella serotypes Virchow and Hadar was seriously repressed. The other serotypes, however, survived in albumen for 24 h. Furthermore, using two different specifically designed egg infection models, it was shown that all strains used in this study were able to penetrate into and multiply inside the yolk at 25°C. These findings indicate that the ability to grow in eggs post lay is not specific for the serotype Enteritidis. In conclusion, comparing strains belonging to different Salmonella serotypes has revealed that most probably a preferential colonization of the reproductive organs and an enhanced survival at 42°C allows the serotype Enteritidis to contaminate eggs.