Porosity of, and bacterial invasion through, the shell of the hen's egg

Abstract

ALTHOUGH bacterial invasion of the developing ovum is known to occur (Haines, 1939), it is fairly clear that the microbial decomposition of eggs encountered in commercial handling is due, in the main, to the invasion of the egg by spoilage-producing micro-organisms after laying. This in turn depends on (a) the inherent porosity of the shell, and (b) the treatment the egg receives, e.g. washing. The present work is an attempt to gain information on these two factors.THE POROSITY OF THE SHELLThe porosity of the shell may be studied (1) by histological methods and (2) by measuring the rate of movement of liquids or gases through the shell under a given pressure gradient. Difficulties have been met in applying both these techniques. The first has given a useful picture not, however, amenable to quantitative interpretation, whilst the second has shown that porosity is a relative term, varying at different points on the shell and in successive eggs from the same hen.(1) Histology P1. IX, fig. 1 is a transverse section ( x 120), normal to the surface, of the eggshell. Four layers can be distinguished. These are: first, the cuticle, composed mainly of fibres of mucin (Moran & Hale, 1936); secondly, the spongy layer consisting of crystals of calcite more or less normal to the cuticle; thirdly, the mammillary layer, also consisting of crystals of calcite, which however do not appear to be definitely orientated; and fourthly, the inner shell membrane.P1. IX, fig. 2 shows a section of a shell, again normal to the surface ( x 100), in which pores or V-shaped openings can be seen stretching from the outside (cuticle not present) to the mammillary layer. It is evident that these pores do not pass right through the shell as has been claimed by Marshall & Cruickshank (1938). The diameter of one of these openings was 13 ,u at the top, 6 , at the bottom. P1. IX, fig. 3 is a section ( x 75), cut parallel with the surface of the shell, in the third or mammillary layer, near the inner shell membrane. The extreme irregularity of the structure is shown, with spaces of various sizes between the calcite crystals which possibly form canals or pores leading to the interior of the egg.

Persistence of contamination of hens' egg albumen in vitro with Salmonella serotypes

“…The pH of the albumen was tested with Whatman indicator paper (range [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”

“…In the other, organisms on the shell are translocated along the pore canals and lodged on the underlying shell membranes. Translocation may occur during egg washing if the wash water is cooler than the egg [5][6][7]. The temperature differential causes a slight negative pressure because the reduction in volume of the contents is greater than that of the shell [5].…”

“…Translocation may occur during egg washing if the wash water is cooler than the egg [5][6][7]. The temperature differential causes a slight negative pressure because the reduction in volume of the contents is greater than that of the shell [5]. This results in a small amount of contaminated water being sucked into an egg [5.…”

Salmonella typhimuriumphage type 141 infections in Sheffield during 1984 and 1985: association with hens' eggs

“…The shell is not impervious to salmonellae; the time taken to penetrate depends on individual shell porosity, moisture, number and type of salmonellae and temperature (Haines & Moran, 1940;Stokes, Osborne & Bayne, 1956;Board, 1966;Sparks & Board, 1985). Penetration may also be aided by cracking or abrasion of the shell, and by poor cuticle layer formation, both of which are common features of batteryproduced eggs.…”

The influence of temperature on the behaviour of mixed bacterial contamination of the shell membrane of the hen's egg

“…Circumstantial evidence suggests that the cuticle at and for a short period following oviposition is immature and hence a relatively ineffective barrier to microbial translocation across the shell [8]. Once mature, the cuticle contributes to the water resistance of the shell and increased pressure is necessary to force water and microorganisms through the pores [9]. To date there appears to have been no detailed study of factors affecting salmonella translocation across the shell.…”