Location: Egg Safety & Quality ResearchTitle: Virulence and metabolic characteristics of Salmonella Enteritidis sefD variants in hens. Author
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2012
Publication Date: 8/1/2012
Citation: Morales, C., Guard, J.Y., Sanchez-Ingunza, R., Shah, D., Harrison, M. 2012. Virulence and metabolic characteristics of Salmonella Enteritidis sefD variants in hens. Applied and Environmental Microbiology. 78:6405-6412. Interpretive Summary: Salmonella Enteritidis is the world’s leading cause of food borne salmonellosis and illness in people is linked strongly to its contamination of eggs produced by otherwise healthy appearing hens. Salmonella Enteritidis has a gene called sefD that helps to make a fimbria, which is a structure that facilitates adhesion of bacteria to host tissues. We found that an abundance of sefD decreases signs of illness in experimentally infected hens and it also enhances the ability of the pathogen to use carbon sources for growth. The gene appears to be better expressed at ambient temperatures in comparison to the body temperatures of people or birds. However, the pathogen appears to shut off the protein once it successfully colonizes the oral mucosa, because the loss of the gene enhances colonization of internal organs, decreases daily egg production and decreases blood calcium levels. We propose that Salmonella Enteritidis in the environment might make this protein in order to efficiently adhere to the avian oral mucosa. There are many details that require further research to know if sefD is indeed a fimbrial gene that is limited to aiding transition from the environment to the host. However, for the purpose of protecting the food supply, the more immediate research need is to investigate if this gene improves vaccines intended to reduce egg contamination by Salmonella Enteritidis.
Technical Abstract: Salmonella Enteritidis is one of a few pathogenic Salmonella enterica serotypes that have SEF14 fimbriae encoded by the sef operon, which consists of 4 co-transcribed genes sefABCD that are regulated by sefR. To explore the function of sefD within the infection pathway resulting in egg contamination, Leghorn hens were injected IM in 3 separate trials with wild-type, sefD mutant, and mutant complemented with a plasmid constitutively expressing sefD. Infection with wild-type and mutant decreased blood calcium and egg production significantly. Analysis by qRT-PCR indicated that complementation with a high copy number plasmid resulted in 200 to 600 fold greater transcription than wild-type or mutant. Thus, wild-type behaved as a functional mutant despite having a complete operon. Phenotype microarray indicated that mutant, wild-type and wild-type transformed with plasmid lacking sefD exhibited catabolite repression. In contrast, the mutant constitutively expressing sefD metabolized sole carbon sources efficiently. Transcription by the complemented mutant was prolonged at 28°C as compared to 37°C and 42°C. These results suggest that lack of sefD increases virulence in the host. In contrast, the presence of sefD appears more likely to have a role in the environment, which is no longer required after transition to the host.