Transcription Factors (TFs) Role in Salmonella Typhimurium and Salmonella Enteritidis Multiplication in Chicken Egg Yolk

Abstract

Egg yolk is an affordable and nutrient-rich matrix that supports the proliferation of pathogenic Salmonella, and the high consumption of raw or undercooked yolk products continues to raise public health concerns as a source of egg-associated Salmonellosis worldwide. The roles of different Salmonella transcriptional factors (TFs) are well characterized for survival in nutrient- rich media and within the host. However, their roles under egg yolk–associated stress conditions remain poorly defined. This study aimed to investigate the growth kinetics of a library of TF mutants of Salmonella enterica serovars Typhimurium and Enteritidis in sterile egg yolk and to compare their growth patterns with those of the isogenic wild type to identify any aberrant growth. In both serovars, deletion of the TF dam, encoding a DNA adenine methylase, caused significant growth inhibition relative to the wild type (p < 0.01 to p < 0.001), whereas deletion of another TF hilD, encoding SPI1 regulation, resulted in enhanced growth (p < 0.05 to p < 0.001). To assess whether the Dam plays a significant role in S. Typhimurium adaptation and proliferation in other food matrices, we conducted growth kinetic assays in bovine whole milk and chicken meat. The strain Δdam also showed reduced proliferation in bovine milk but not in chicken meat, suggesting a matrix-specific regulatory role of Dam. Furthermore, the consistent directional effects of DNA adenine methyltransferase (Dam) and the SPI-1 regulator (HilD) observed in both serovars suggest conserved global regulatory mechanisms that drive pathogen adaptation to the egg yolk environment. Together, these findings highlight the importance of regulated transcriptional control for Salmonella survival and proliferation in egg yolk-stress-associated niches.