Antimicrobial activity of lipophilic avian eggshell surface extracts.

The avian eggshell cuticle is the waxy outermost layer of the mineralized eggshell in direct contact with the environment. In this study, lipophilic eggshell surface extracts from three domestic species were evaluated for their antimicrobial activity. Chicken and goose extracts demonstrated potent bactericidal activity against both Gram-positive and Gram-negative bacteria, while activity could not be detected for duck eggshell surface extracts. Using the chicken as a model species, evaluation of albumen, fecal material, and uropygial gland extracts eliminated these as a potential source of the observed activity. Results suggest that lipophilic components are incorporated into the egg during its formation and play a role in antimicrobial defense. This study represents the first successful extraction and evaluation of lipophilic antimicrobial components from the avian egg.

Antimicrobial activity of the Anseriform outer eggshell and cuticle.

The avian eggshell is a complex, multifunctional biomineral composed of a calcium carbonate mineral phase and an organic phase of lipids and proteins. The outermost layer of the eggshell, the eggshell cuticle, is an organic layer of variable thickness composed of polysaccharides, hydroxyapatite crystals, lipids and glycoprotein. In addition to regulating gas exchanges, the eggshell cuticle may contain antimicrobial elements. In this study, we investigated the antimicrobial activity of eggshell cuticle and outer eggshell protein extracts from four Anseriform species: wood duck (Aix sponsa), hooded merganser (Lophodytes cucullatus), Canada goose (Branta canadensis) and mute swan (Cygnus olor). Cuticle and outer eggshell protein was extracted by urea or HCl treatment of eggs. C-type lysozyme, ovotransferrin and an ovocalyxin-32-like protein were detected in all extracts. Cuticle and outer eggshell protein extracts inhibited the growth of Staphylococcus aureus, Escherichia coli D31, Pseudomonas aeruginosa and Bacillus subtilis. The presence of active antimicrobial proteins within the avian cuticle and outer eggshell suggests a role in antimicrobial defense. Protein extracts from the cavity nesting hooded merganser were especially potent. The unique environmental pressures exerted on cavity-nesting species may have led to the evolution of potent antimicrobial defenses.

Enhanced C-type lysozyme content of wood duck (Aix sponsa) egg white: an adaptation to cavity nesting?

Abstract Wild waterfowl species often nest in conditions where high humidity and microbial contamination may influence egg survival and quality. Albumen is traditionally regarded as the major impediment to microbial contamination of eggs, and its composition and activity may be selected by environmental pressures. Egg white protein from the eggs of wood duck (Aix sponsa), hooded merganser (Lophodytes cucullatus), Canada goose (Branta canadensis), and mute swan (Cygnus olor) was evaluated in order to compare the antimicrobial defenses of these species. Ovotransferrin and ovalbumin were identified in all species, but c-type lysozyme was present only in wood duck and hooded merganser egg white samples. Wood duck egg white showed the greatest bacterial activity as well as the highest lysozyme content. Egg white from wood duck and hooded merganser possessed greater lysozyme activity under acidic conditions, suggesting a c-type lysozyme with a pH optimum lower than that of Gallus gallus c-type lysozyme or the presence of g-type lysozyme. Ovotransferrin bacteriostatic activity appeared to be similar across the species investigated. The results suggest that lysozyme and ovotransferrin play a role in the antimicrobial defense of the avian egg. High levels of the broad-acting c-type lysozyme appear to have evolved in the albumen of the wood duck in order to ensure proper development of the embryo in the humid conditions of the cavity nest.