Purpose: To identify S. enterica Enteritidis-specific genes, which are absent in the genomes of serovar Salmonella Typhimurium and Typhi, relevant to its survival in the egg albumen.
Methods: Using comparative genomic analysis, we found 94 genes in S. enterica Enteritidis which are absent in the genomes of Typhimurium and Typhi. Among these genes, 25 in-frame gene deletion mutants were constructed in Enteritidis PT4. Overnight cultures of wild-type PT4 and each mutant were adjusted to a final concentration of 105 CFU/ml and thoroughly mixed with 5 ml of organic, antibiotic-free chicken egg albumen. Samples were incubated at 37°C for up to 72 h. Samples were taken at 0, 24, 48, and 72 h and serial dilutions were plated onto LB and XLD agars. Data were analyzed using Prism GraphPad and R statistical software. A P-value of less than 0.05 was considered significant.
Results: The Salmonella Enteritidis gene deletion mutants which had significantly lower survival in egg-albumen than the wild-type strain (greater than 3 log CFU) were sen0998 and sen0276 (less than 2 log CFU) at 48 h incubation, indicating that these genes may contribute to S. enterica survival in egg albumin. At 72 h, the wild-type and all gene deletion mutants declined from 5 log CFU to less than 1 log CFU at 37°C incubation.
Significance: Constructed gene deletion mutants will help determine the relative functions of different genes in Salmonella Enteritidis. The data of this study will aid in understanding the pathogenicity of Salmonella Enteritidis and will help in the prevention of outbreaks associated with egg albumen.