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International audience; A recent work revealed that egg white (EW) at 45°C exhibits powerful bactericidal activity against S. enterica serovar Enteritidis, which is surprisingly little affected by removal of the >10 kDa EW proteins. Here, we sought to identify the major EW factors responsible for this bactericidal activity by fractionating EW using ultrafiltration and nanofiltration and by characterizing the physicochemical and antimicrobial properties of the resulting fractions. In particular, 22 peptides were identified by nano-LC/MS-MS and the bactericidal activities of representative peptides (with predicted antimicrobial activity) were further assessed. Two peptides (FVPPVQR and GDPSAWSWGAEAHS) were found to be bactericidal against S. enterica serovar Enteritidis at 45°C when provided in an EW environment. Nevertheless, these peptides contribute only part of this bactericidal activity, suggesting other, yet to be determined, antimicrobial factors.

Conference: 11th International Symposium on Biometals (Biometals) Location: Ottawa, CANADA Date: 2018; Salmonella enterica serovar Enteritidis (SE) is the most frequently-detected Salmonella in foodborne outbreaks in the European Union. Among such outbreaks, egg and egg products were identifiedas the most common vehicles of infection. Possibly, the major antibacterial property of egg white is ironrestriction, which results from the presence of the ironbinding protein, ovotransferrin. To circumvent ironrestriction, SE synthesise catecholate siderophores (i.e. enterobactin and salmochelin) that can chelateiron from host iron-binding proteins. Here, we highlight the role of lipocalin-like proteins found in eggwhite that could enhance egg-white iron restriction through sequestration of certain siderophores, includingenterobactin. Indeed, it is now apparent that the egg-white lipocalin, Ex-FABP, can inhibit bacterialgrowth via its siderophore-binding capacity in vitro. However, it remains unclear whether Ex-FABP performssuch a function in egg white or during bird infection. Regarding the two other lipocalins of eggwhite (Cal-c and a-1-glycoprotein), there is currently no evidence to indicate that they sequestersiderophores.

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 tempertaures, 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 utilisation genes, despite no evidence indicating the presence of these substrates in egg white.

International audience