|He, Louis - Haiqi|
Submitted to: FEMS Immunology and Medical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2008
Publication Date: 3/19/2008
Citation: Chang, J., Pang, E., He, L.H., Kwong, J. 2008. Identification of novel attenuated Salmonella Enteritidis mutants. FEMS Immunology and Medical Microbiology. 53:26-34.
Interpretive Summary: Salmonella Enteritidis is a major food-borne bacterial pathogen that causes illness in humans. Since many S. Enteritidis-related illness in humans can be linked to chicken eggs, one approach to reduce this incidence is to eliminate S. Enteritidis from the food chain or more specifically, from egg-laying hens. For this strategy to be effective, a good vaccination program is required to prevent S. Enteritidis from living inside chickens. We performed genetic mutation experiments to make mutant strains of S. Enteritidis that will not survive inside chickens, but can be used as vaccine strains to stimulate the chicken immune system to fight the real disease-causing Salmonella Enteritidis. Out of 384 mutants, we have found one mutant strain of Salmonella Enteritidis that meets the criteria for use as a vaccine. This information is important to the poultry industries because it offer a new vaccine strategy to produce healthy chicken and reduce the food-borne disease in human.
Technical Abstract: Infection of egg-laying hens results in symptomless carriage but in young chicks it causes paratyphoid disease. Little is known about whether S. Enteritidis requires other genes additional to known virulence genes for systemic infection of young chickens. A transposon insertion library was created using S. Enteritidis 10/02, which yielded 1246 mutants. Out of 384 mutants that were screened in chickens for attenuation (30.8% of insertion library), 12 (3.1%) were found to have an LD50 at least 100 times that of the parental strain. Sequencing revealed that mutants had insertions in genes that were involved in the biosynthesis of lipopolysaccharide, cell membrane integrity or assembly, ATP biosynthesis, transcriptional regulation of virulence and one mutant had an insertion in the yhbC gene, which has an unknown function. Evaluation of the in vitro virulence characteristics of deltayhbC revealed that it was less able to survive within a chicken macrophage cell line (HD11), less resistant to reactive oxygen and nitrogen intermediates and had a retarded growth rate compared to the parental strain. However, no significant difference was found in the ability to grow after prolonged stationary phase or to resist low pH conditions, sodium deoxycholate and chicken serum. Chickens challenged with deltayhbC were able to clear the organism from the liver and spleen at least one week faster than the parental strain and chickens were able to develop specific serum IgG antibodies against deltayhbC.