Haigh T, Betts W B
Institute for Applied Biology, University of York, Heslington, Great Britain.
Microbios. 1991;68(276-277):137-46.
Scanning electron micrographs of shell surfaces revealed a highly fissured outer layer with few open pores on brown eggs but many on white eggs. Total removal of the cuticle with solvents was difficult but partial removal with surface etching was possible using concentrated nitric acid. Staining methods to estimate the number of pores were unsatisfactory but it was possible to detect and count pores on micrographs, as pore mouths were usually associated with depressions and cuticle disruptions. Additionally, porosity could be estimated by measuring the distance between pores along fractured edges of samples. Egg shell contents were replaced with nutrient agar and incubated in Escherichia coli broth. Colonies were subsequently isolated from the agar, indicating that the barrier properties of shells and membranes had been compromised. Experiments with isolated inner shell membranes showed that these posed no significant barrier to E. coli. The exposure of whole intact eggs to E. coli broth followed by seep filtration and microbiological analysis of egg contents, indicated that bacteria had entered the eggs. The degree of infection was correlated with the pole of the egg in contact with the E. coli broth and was attributed to the increased porosity of the blunt pole of the egg compared with that of the apex. Similar experiments immersing eggs into broth inoculated with a Salmonella strain resulted in contamination of the egg contents with this organism.
蛋壳表面的扫描电子显微镜图像显示，褐壳蛋的外层有高度裂隙，开孔较少，而白壳蛋的开孔较多。用溶剂完全去除角质层很困难，但用浓硝酸进行表面蚀刻可以部分去除。估计气孔数量的染色方法并不理想，但在显微照片上可以检测和计数气孔，因为气孔口通常与凹陷和角质层破坏有关。此外，可以通过测量样品断裂边缘上气孔之间的距离来估计孔隙率。将蛋壳内容物用营养琼脂替代，并在大肠杆菌肉汤中培养。随后从琼脂中分离出菌落，表明蛋壳和内膜的屏障特性已受到损害。对分离出的内壳膜进行的实验表明，这些膜对大肠杆菌没有显著的屏障作用。将完整的全蛋暴露于大肠杆菌肉汤中，然后进行渗滤并对蛋内容物进行微生物分析，结果表明细菌已进入蛋中。感染程度与蛋与大肠杆菌肉汤接触的一端有关，这归因于蛋钝端的孔隙率比顶端高。将蛋浸入接种了沙门氏菌菌株的肉汤中的类似实验导致蛋内容物被这种微生物污染。
