Egg-associated transmission to humans seems to be characteristic of the Salmonella serotype Enteritidis, explaining why this particular serotype has caused a worldwide pandemic since the mid '80s, according to Filip Van Immerseel of the University of Ghent in Belgium in a paper in the journal, Gut Pathogens. Salmonella Enteritidis is much more capable to colonise persistently the laying hen reproductive tract and to survive in the hostile egg white than other serotypes.

Presentation of the hypothesis

Dr Van Immerseel hypothesises that stress-induced survival mechanisms enable the serotype Enteritidis to colonise the oviduct persistently, without causing damage and excessive inflammation, and to cope with the antimicrobial compounds present in egg white.

Testing the hypothesis

To test the hypothesis, first of all Salmonella Enteritidis genes that are essential for colonisation of the oviduct and survival in eggs need to be identified.

Comparative genomics tools should be used to identify genes or pathogenicity islands that are present in Salmonella Enteritidis and not in the multiple non egg-contaminating serotypes.

High-throughput signature-tagged-mutagenesis approaches, coupled to micro-array detection of the genes that lead to an attenuated phenotype when mutated is proposed as an ideal tool to identify genes involved in oviduct colonization and egg white survival.

Identifying the stressors and antibacterial molecules in the oviduct and in the egg white that limit colonization or survival of non-Enteritidis serotypes is a second important objective that can theoretically be achieved using screenings of expressed oviduct cDNA libraries for their antibacterial activity against strains from multiple serotypes.

Finally, the effect of contact with these stressors in the oviduct or egg white on Salmonella gene expression will need to be analyzed, in order to clarify whether serotype Enteritidis-specific regulation of certain stress-survival pathways are either or not present.

Implications of the hypothesis

Knowledge on the pathogenesis of egg infections would furthermore give insights that might be extrapolated to other biological interactions, in which a highly specialised bacterial pathogen resists the host response in a specific biological niche. In addition, this information can be of value in developing early warning criteria to identify emerging egg-associated Salmonella strains and in developing safe live attenuated vaccine strains.

Reference

Van Immerseel F. 2010. Stress-induced survival strategies enable Salmonella Enteritidis to persistently colonize the chicken oviduct tissue and cope with antimicrobial factors in egg white: A hypothesis to explain a pandemic. Gut Pathogens, 2:23. doi:10.1186/1757-4749-2-23.

Further Reading

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You can view the full report (as a provisional PDF) by clicking here.

December 2010