Global Gene-expression Analysis of the Response of Salmonella Enteritidis to Egg White Exposure Reveals Multiple Egg White-imposed Stress Responses

Abstract

Chicken egg white protects the embryo from bacterial invaders by presenting an assortment of antagonistic activities that combine together to both kill and inhibit growth. The key features of the egg white anti-bacterial system are iron restriction, high pH, antibacterial peptides and proteins, and viscosity. Salmonella enterica serovar Enteritidis is the major pathogen responsible for egg-borne infection in humans, which is partly explained by its exceptional capacity for survival under the harsh conditions encountered within egg white. However, at temperatures up to 42°C, egg white exerts a much stronger bactericidal effect on S. Enteritidis than at lower temperatures, although the mechanism of egg white-induced killing is only partly understood. Here, for the first time, the impact of exposure of S. Enteritidis to egg white under bactericidal conditions (45°C) is explored by global-expression analysis. A large-scale (18.7% of genome) shift in transcription is revealed suggesting major changes in specific aspects of S. Enteritidis physiology: induction of egg white related stress-responses (envelope damage, exposure to heat and alkalinity, and translation shutdown); shift in energy metabolism from respiration to fermentation; and enhanced micronutrient provision (due to iron and biotin restriction). Little evidence of DNA damage or redox stress was obtained. Instead, data are consistent with envelope damage resulting in cell death by lysis. A surprise was the high degree of induction of hexonate/hexuronate utilization genes, despite no evidence indicating the presence of these substrates in egg white.

Role of yoaE Gene Regulated by CpxR in the Survival of Salmonella enterica Serovar Enteritidis in Antibacterial Egg White

“…However, revelation of this resistance mechanism requires further determination of the yoaE function, which is as yet still unclear. CpxR/A is a critical TCS contributing to the survival of S. Enteritidis in egg white and functions by extensively regulating genes that help bacteria resist envelope stress and alkaline pH (16,17). In the present study, we proved that yoaE gene is a CpxR/A regulon and that this regulatory relationship should be conserved in neighboring species, indicating that yoaE should be envelope stress-related gene, which provides clues to the yoaE gene function.…”

“…Previous studies have shown that S. Enteritidis mobilizes utilizes multiple mechanisms to counteract antibacterial factors in egg white. Genes or pathways involved in iron absorption (15)(16)(17), biotin synthesis (16)(17)(18), DNA replication and repair (4,17,19), alkaline pH adaptation (17), osmotic stress adaptation (17), envelope damage repair (including peptidoglycan biosynthesis and remodeling) (4,17), amino acid transport and metabolism (4), lipopolysaccharide metabolism (4,18,20,21), and cell motility (22) were found to be important for S. Enteritidis survival in egg white.…”

“…The two-component regulatory system (TCS) CpxR/A plays a central and critical role in bacterial envelop damage repair and alkaline pH adaption in egg white (16,17). Once activated in egg white, CpxR/A upregulated genes involved in periplasmic space homeostasis, peptidoglycan cross-linking, and remodeling and envelope cross-linking to combat envelope stress caused by egg white; they also upregulated cation/antiporter chaA and downregulated the respiratory complexes (the nuo and cyo operons) to increase proton import and to decrease proton export, therefore maintaining bacterial pH homeostasis in the alkaline egg white (16,17). In addition, deletion of cpxR gene made the survival ability of S. Enteritidis in egg white dramatically reduced, which further proved the importance of this TCS (17).…”

Ethanol Adaptation Strategies in Salmonella enterica Serovar Enteritidis Revealed by Global Proteomic and Mutagenic Analyses

“…In fact, there is increasing evidence implicating the role of enterobactin in bacterial stress responses. For example, enterobactin biosynthesis and uptake were induced following exposure of S. Enteritidis to egg white to facilitate iron acquisition, thus providing a survival advantage to this bacterium (16,49). Peralta et al found that enterobactin protected E. coli against oxidative stress and that this effect was independent of its capacity to scavenge iron (50).…”

Comparative Genomic Analysis and Characterization of Two Salmonella enterica Serovar Enteritidis Isolates From Poultry With Notably Different Survival Abilities in Egg Whites

“…The biotin synthase gene bioB is required for the survival of Salmonella Enteritidis in egg whites ( Raspoet et al, 2014 ). Moreover, bioA, B, C, D , and F are transcriptionally upregulated in Salmonella Enteritidis during growth in whole egg or egg white model medium ( Jakociune et al, 2016 ; Baron et al, 2017 ). In our study, the single nucleotide variation (T433G, S145A) in the bioC gene was predicted to be deleterious in silico and suggested that this nsSNP had drastic functional consequences ( Supplementary Table S2 ).…”