Characterization of egg white antibacterial properties during the first half of incubation: A comparative study between embryonated and unfertilized eggs

Abstract

Egg white is an important contributor to the protection of eggs against bacterial contaminations during the first half of incubation (day zero to 12), prior to the egg white transfer into the amniotic fluid to be orally absorbed by the embryo. This protective system relies on an arsenal of antimicrobial proteins and on intrinsic physicochemical properties that are generally unfavorable for bacterial multiplication and dissemination. Some changes in these parameters can be observed in egg white during egg storage and incubation. The aim of this work was to characterize changes in the antibacterial potential of egg white in embryonated eggs (FE) during the first half of incubation using unfertilized eggs (UF) as controls. Egg white samples were collected at day zero, 4, 8, and 12 and analyzed for pH, protein concentration, and protein profile. Antibacterial properties of egg white proteins were evaluated against Listeria monocytogenes, Streptococcus uberis, Staphylococcus aureus, Escherichia coli, and Salmonella Enteritidis. During incubation, differential variations of egg white pH and protein concentrations were observed between UF and FE. At equal protein concentrations, similar activities against L. monocytogenes and S. uberis were observed for FE and UF egg white proteins. A progressive decline in these activities, however, was observed over incubation time, regardless of the egg group (UF or FE). SDS-PAGE analysis of egg white proteins during incubation revealed discrete changes in the profile of major proteins, whereas the stability of some less abundant antimicrobial proteins seemed more affected. To conclude, the antibacterial activity of egg white proteins progressively decreased during the first half of egg incubation, possibly resulting from the alteration of specific antimicrobial proteins. This apparent decline may be partly counterbalanced in embryonated eggs by the increase in egg white protein concentration. The antibacterial potential of egg white is very effective during early stages of embryonic development but its alteration during incubation suggests that extra-embryonic structures could then progressively ensure protective functions.

The Unique Features of Proteins Depicting the Chicken Amniotic Fluid

“…Some proteolytic activities (18) have been however detected in AF at ED11, but, because of the low abundance of the corresponding proteins, the biological significance of these activities in AF remains questionable as compared to the egg yolk, which concentrates hydrolytic enzymes (43,49). The same observation can be made for the faint antibacterial activities detected at ED11 in the chicken AF, compared with the egg white, which concentrates high amounts of antibacterial proteins such as active lysozyme (30,42). and which functions are still speculative.…”

“…All samples (raw, flow-through and eluted fractions) were analyzed by SDS-PAGE. Protein profiles of egg white at ED11 and ED16 were compared to previously published data for experimental validation (27,30). For antibacterial assays, at least three independent assays were performed on Listeria monocytogenes and Salmonella enterica…”

“…The HBP fraction of egg white has been previously reported to contain antibacterial proteins and activities (27,30). In order to explore the regulation of egg white antibacterial activities all along incubation, we performed antibacterial assays on egg white HBP, sampled and purified at ED0, 8 and 14 (Fig.…”

Dynamics of Structural Barriers and Innate Immune Components during Incubation of the Avian Egg: Critical Interplay between Autonomous Embryonic Development and Maternal Anticipation

“…In a freshly laid egg, whether fertilized or not, the EW pH increases rapidly from 7.6 to 9.0, attributable to the diffusion of CO 2 through the ES [84]. This phenomenon not only affects the survival and growth of bacteria, but also their flagellar mobility and the oxidative stress experienced by bacteria [85].…”

“…Direct transfer of gut proteins to the allantoic sac is also likely to occur [83]. EW anti- Listeria monocytogenes and anti- Streptococcus uberis activities are maintained during embryonic development up to ED12 [84], and EW antibacterial proteins have been shown to be active even after their transfer into the amniotic sac [20]. …”