Dry-Resistance of Salmonella enterica subsp enterica Serovar Enteritidis is Regulated by Both SEp22, a Novel Pathogenicity-Related Factor of Salmonella, and Nutrients

Environmental isolates of Salmonella enterica serover Enteritidis (S. Enteritidis) clones were grown to the logarithmic phase, washed and re-suspended in saline or Luria-Bertani (LB) medium, and then 10-mu L aliquots of the suspensions were dried overnight at room temperature. The dried bacteria were mixed with 1 mL of ice-cold PBS, suspended and examined for colony-forming activity. All of the pathogenic clones with high levels of SEp22, identical to Salmonella Dps, maintained good viability if suspended in LB medium prior to drying. However, none of the non-virulent strains, exhibiting low levels of SEp22, survived. Similar results were obtained with sep22-knocked out mutants, suggesting that SEp22 is important for the acquisition of dry-resistance. Nutritional factors, such as LB medium, cabbage extracts, and egg yolk but not egg white, were shown to be necessary for the acquisition of dry-resistance, because none of the clones remained viable irrespective of SEp22 expression if suspended in saline. Scanning electron micrograms also supported the importance of nutrition, showing re-growth of the bacteria after drying in LB but not in saline. These results suggest the importance of both SEp22 expression and nutrients for the acquisition of dry-resistance by S. Enteritidis.