Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.
Evolutionary Ecology, Naturalis Biodiversity Center, Leiden, Netherlands.
Front Immunol. 2022 Feb 25;13:838525. doi: 10.3389/fimmu.2022.838525. eCollection 2022.
Cleidoic eggs possess very efficient and orchestrated systems to protect the embryo from external microbes until hatch. The cuticle is a proteinaceous layer on the shell surface in many bird and some reptile species. An intact cuticle forms a pore plug to occlude respiratory pores and is an effective physical and chemical barrier against microbial penetration. The interior of the egg is assumed to be normally sterile, while the outer eggshell cuticle hosts microbes. The diversity of the eggshell microbiome is derived from both maternal microbiota and those of the nesting environment. The surface characteristics of the egg, outer moisture layer and the presence of antimicrobial molecules composing the cuticle dictate constituents of the microbial communities on the eggshell surface. The avian cuticle affects eggshell wettability, water vapor conductance and regulates ultraviolet reflectance in various ground-nesting species; moreover, its composition, thickness and degree of coverage are dependent on species, hen age, and physiological stressors. Studies in domestic avian species have demonstrated that changes in the cuticle affect the food safety of eggs with respect to the risk of contamination by bacterial pathogens such as and . Moreover, preventing contamination of internal egg components is crucial to optimize hatching success in bird species. In chickens there is moderate heritability (38%) of cuticle deposition with a potential for genetic improvement. However, much less is known about other bird or reptile cuticles. This review synthesizes current knowledge of eggshell cuticle and provides insight into its evolution in the clade reptilia. The origin, composition and regulation of the eggshell microbiome and the potential function of the cuticle as the first barrier of egg defense are discussed in detail. We evaluate how changes in the cuticle affect the food safety of table eggs and vertical transmission of pathogens in the production chain with respect to the risk of contamination. Thus, this review provides insight into the physiological and microbiological characteristics of eggshell cuticle in relation to its protective function (innate immunity) in egg-laying birds and reptiles.
胶性卵具有非常高效和协调的系统，可保护胚胎免受外部微生物的侵害，直到孵化。壳层是许多鸟类和一些爬行动物物种壳表面的蛋白质层。完整的壳层形成一个孔塞，以堵塞呼吸孔，是防止微生物渗透的有效物理和化学屏障。蛋壳内被认为是无菌的，而外壳的角质层则有微生物栖息。蛋壳微生物组的多样性来源于母体微生物群和筑巢环境的微生物群。蛋壳的表面特性、外层水分层以及构成壳层的抗菌分子的存在决定了蛋壳表面微生物群落的组成。禽类角质层影响蛋壳的润湿性、水蒸气传导率，并调节各种地面筑巢物种的紫外线反射率；此外，其组成、厚度和覆盖度取决于物种、母鸡年龄和生理应激源。对家禽物种的研究表明，角质层的变化会影响鸡蛋的食品安全，增加细菌病原体污染的风险，如 和 。此外，防止内部卵成分的污染对于优化鸟类物种的孵化成功率至关重要。在鸡中，角质层沉积具有中等的遗传力（38%），具有遗传改良的潜力。然而，关于其他鸟类或爬行动物的角质层，人们知之甚少。本文综述了蛋壳角质层的现有知识，并深入探讨了其在爬行动物进化中的作用。详细讨论了蛋壳微生物组的起源、组成和调控，以及角质层作为卵防御第一道防线的潜在功能。我们评估了角质层的变化如何影响食用蛋的食品安全以及生产链中病原体的垂直传播，从而评估了污染的风险。因此，本文综述了与产卵鸟类和爬行动物的保护功能（先天免疫）相关的蛋壳角质层的生理和微生物学特征。
