The presence of the dam gene is important for the proliferation of Salmonella Typhimurium in egg yolk.

Chicken egg is an important vector of global salmonellosis. However, mechanistic insights into Salmonella proliferation in eggs, particularly in the yolk, are lacking. Here, we employed a suite of eight regulatory mutants to identify the distinct stresses Salmonella encounters during yolk proliferation. The regulatory mutants of Salmonella Typhimurium ST4/74 (ST4/74) were inoculated into pasteurized egg yolk, and their growth kinetics were compared individually with those of the isogenic wild type. Of the eight mutants, the null mutant of the dam gene, which encodes DNA adenine methyltransferase, exhibited significantly reduced growth compared to the wild type. The presence of the dam gene was further demonstrated to be important for Salmonella proliferation in bovine milk but not in chicken meat. Null mutants of the gene encoding the SPI-1 regulatory protein HilD and of oxidative stress response proteins such as KatN, SodA, and MntH grew better than the wild type in yolk. Null mutants of the same genes in S. Enteritidis P125109 behaved similarly to those in ST4/74, suggesting a more global role for these genes in the Salmonella egg yolk survival. Overall, our findings provide early insights into the mechanisms Salmonella uses to survive in egg yolk.