Location: Egg Safety & Quality ResearchTitle: Salmonella Enteritidis strains from poultry show differential responses to acid stress, oxidative stress and survival in the egg albumen Author
Submitted to: Food Borne Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2011
Publication Date: 2/3/2012
Citation: Shah, D.H., Casavant, C., Hawley, Q., Addwebi, T., Call, D.R., Guard, J.Y. 2012. Salmonella Enteritidis strains from poultry show differential responses to acid stress, oxidative stress and survival in the egg albumen. Food Borne Diseases. 9(3):258-264. Interpretive Summary: Expression of genes that facilitate the ability of a bacterium to cause disease can have multiple layers of control. Sometimes a mutation in the gene producing the protein alters disease potential, but other times the mutation might be in a different region that alters the regulation of the gene in question. Regardless of where the mutation is, the way the bacteria acts on the host can look the same if the ultimate outcome is a change in the gene most immediately responsible for causing disease. This research shows that the gene rpoS, a stress regulatory gene producing a factor referred to as sS, is a gene likely to be mutated in Salmonella Enteritidis either directly at the site of the gene or indirectly at the level of a regulator. Salmonella Enteritidis appears to change its ability to cause disease through small mutations. In this case an insertion of one nucleotide was found to be the culprit for changing the behavior of the pathogen.
Technical Abstract: Salmonella Enteritidis is the major food-borne pathogen primarily causing human infection through contaminated chicken meat and eggs. We recently demonstrated that S. Enteritidis strains from poultry differ in their ability to invade human intestinal cells and cause disease in orally challenged mice. Here we hypothesized that the differential pathogenicity of S. Enteritidis strains is due to the differential fitness in the adverse environments that may be encountered during infection in the host. The response of a panel of six S. Enteritidis strains to acid stress, oxidative stress, survival in egg albumen and the ability to cause infection in chickens were analyzed. This analysis allowed classification of strains into two categories: stress- sensitive and stress- resistant, with the former showing significantly (P<0.05) reduced survival in acidic (gastric phase of infection) and oxidative (intestinal and systemic phase of infection) stress. Stress-sensitive strains also showed impaired intestinal colonization and systemic dissemination in orally inoculated chickens and failed to survive/grow in egg albumen. Comparative genomic hybridization microarray analysis revealed no differences at the discriminatory level of the whole gene content between stress-sensitive and stress-resistant strains. However, sequencing of rpoS, a stress-regulatory gene, revealed that one of the three stress-sensitive strains carried an insertion mutation in the rpoS resulting in truncation of sS. Finding that one of the stress-sensitive strains carried an easily identifiable small polymorphism within a stress-response gene suggests that the other strains may also have small polymorphisms elsewhere in the genome, which likely impact regulation of stress or virulence associated genes in some manner.