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Title: Correlation of phenotype with the genotype of egg-contaminating salmonella enterica serovar enteritidis

item Morales, Cesar
item Frye, Jonathan
item Guard, Jean

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2005
Publication Date: 8/1/2005
Citation: Morales, C., Porowollik, S., Frye, J.G., Kinde, H., Mcclelland, M., Guard, J.Y. 2005. Correlation of phenotype with the genotype of egg-contaminating salmonella enterica serovar enteritidis. Applied and Environmental Microbiology. 71(8):4388-4399.

Interpretive Summary: Salmonella enteritidis is an important source of food borne illness in humans, in part because of its unique ability among 2500 different types of Salmonella to cause egg contamination. New technologies, namely DNA microarray and PhenotypeMicroarrayTM, are now available to study how the genetics of a bacterium is related to its growth in the on-farm environment. Application of these technologies in addition to other more traditional assays showed that strains with different abilities to cause egg contamination have very different growth patterns. Thus, very large biological differences exist between strains that have nearly identical genetics. This research impacts our understanding of how bacteria evolve to cause food borne illness in humans.

Technical Abstract: The genotype of Salmonella enterica serovar Enteritidis was correlated to phenotype using DNA-DNA microarray hybridization, ribotyping, and Phenotype MicroArrayTM to compare three strains that differed in colony morphology and phage type. Two PT13A strains that varied in biofilm formation had DNA sequence similar to bacteriophage Fels2, whereas a PT4 strain had DNA sequence with some similarity to bacteriophage ST64b. The two PT13A strains that had different phenotypes had different ribotype patterns but had no differences in DNA hybridization results. Phenotype MicroArray analysis indicated that the three strains had similar growth profiles at 37°C. In contrast, wild-type S. enteritidis PT13A grew significantly better in 20% more growth conditions at 25°C than did the biofilm-forming PT13A strain. S. enteritidis PT4 had a growth profile that was intermediate to the two PT13A strains at 25°C. Further analysis of Phenotype MicroArray data suggested that PT4 S. enteritidis had a temperature-influenced dimorphic metabolism that at lower temperatures resembled that of biofilm-forming strains and at higher temperatures resembled wild-type. Thus, some strains of S. enteritidis may express two phenotypes from a single genome, whereas others have specialized and express only one. This concept was further investigated by assay for antibiotic resistances and evaluation of growth in selectively supplemented minimal media. Overall, these results show that remarkably minor evolutionary events greatly alter the physiology of S. enteritidis. The pandemic of S. enteritidis thus appears to be primarily an example of how adaptive radiation can impact the safety of the food supply.