Table Of ContentMicrobiology of the Avian Egg
Microbiology of the Avian Egg
Edited by
R.G. Board
Professor of Food Microbiology
University of Bath
UK
and
R. Fuller
Intestinal Microbiology Consultant
Reading
UK
m
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
First edition 1994
© 1994 Springer Science+Business Media Dordrecht
Origina1ly published by Chapman & Hali in 1994
Softcover reprint ofthe hardcover Ist edition 1994
Typeset in 10/12 pt Palatino by ROM-Data Corporation, Falmouth,
Comwall
ISBN 978-1-4613-6335-4 ISBN 978-1-4615-3060-2 (eBook)
DOI 10.1007/978-1-4615-3060-2
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Contents
List of contributors ix
Preface Xl
1 Hen's egg shell structure and function 1
S.E. Solomon, M.M. Bain, S. Cranstoun and V. Nascimento
1.1 The cuticle 1
1.2 The pores 4
1.3 The true shell 4
1.4 The membranes 18
References 22
2 Shell accessory materials: structure and function 25
N.H. C. Sparks
2.1 Introduction 25
2.2 Chemical composition and structure 25
2.3 Function of shell accessory materials 33
2.4 Egg washing/ sanitizing 37
References 40
3 The egg: a compartmentalized, aseptically packaged food 43
RG. Board, C. Clay, J. Lock and J. Dolman
3.1 Compartmentalization 43
3.2 An aseptically packaged food 49
3.3 Antimicrobial defence 51
3.4 Chemotaxis and egg infection 55
3.5 Colonization of the gut 57
References 58
Vl Contents
4 Trans-shell transmission 63
J. Bruce and E.M. Drysdale
4.1 Introduction 63
4.2 Routes of transmission 63
4.3 Factors affecting trans-shell infection of eggs 65
4.4 Control of trans-shell transmission 81
4.5 Summary 86
References 86
5 Contamination of eggs with potential human pathogens 93
TI Humphrey
5.1 Introduction 93
5.2 Historical background 93
5.3 Salmonella contamination of eggs 94
5.4 Eggs and egg dishes as vehicles for human salmonellosis 102
5.5 Salmonella infection in laying hens 105
5.6 Other pathogens 111
References 112
6 The microflora of the alimentary tract and avian pathogens: 117
translocation and vertical transmission
P.A. Barrow
6.1 Introduction 117
6.2 General strategies for vertical transmission and survival in 117
the tissues
6.3 The normal microflora of the alimentary tract of the chicken 119
6.4 Factors affecting the composition of the flora 122
6.5 Translocation of the indigenous gut flora 123
6.6 Vertical transmission of avian pathogens 126
6.7 Summary 135
References 136
7 Contaminants of liquid egg products 139
WI Stadelman
7.1 Introduction 139
7.2 Eggshell egg contamination 139
7.3 Liquid egg contaminants 144
7.4 Summary 148
References 148
Contents vii
8 Effects of processing on the microbiology of eggs 153
KC. Baker and C. Bruce
8.1 Introduction 153
8.2 Egg washing 154
8.3 Preservation of eggs 156
8.4 Egg breaking 162
8.5 Long-term preservation of liquid egg 165
8.6 Microbiological concerns in developing new market forms 166
8.7 Safe preparation of eggs and egg dishes at home 170
8.8 Summary 171
References 172
Index 175
Con tribu tors
M.M. Bain, Poultry Research Group, Department of Veterinary Anatomy,
Glasgow University Veterinary School, Bearsden Road, Glasgow, G61
1QH
RC. Baker, Professor Emeritus, Departments of Poultry Science and Food
Science, Rice Hall, Cornell University, Ithaca, NY 14853, USA
P.A. Barrow, AFRC, Institute of Animal Health, Compton Laboratory,
Compton, Nr Newbury, Berkshire, RG16 ONN
RG. Board, School of Biological Sciences, The University of Bath, Bath,
Avon, BA2 7AY
C. Bruce, Research Support Specialist, Department of Food Science, Rice
Hall, Cornell University, Ithaca, NY 14850, USA
J. Bruce, Food Science and Technology Department, Scottish Agricultural
College, Auchincruive, Ayr, KA6 5HW
C. Clay, School of Biological Sciences, The University of Bath, Bath, A von,
BA27AY
S. Cranstoun, Poultry Research Group, Department of Veterinary Anatomy,
Glasgow University Veterinary School, Bearsden Road, Glasgow, G61
1QH
J. Dolman, School of Biological Sciences, The University of Bath, Bath, Avon,
BA27AY
E.M. Drysdale, Food Science and Technology Department, Scottish Agricul
tural College, Auchincruive, Ayr, KA6 5HW
T.J. Humphrey, Food Unit, Public Health Laboratory, Church Lane, Exeter,
EX25AD
J. Lock, School of Biological Sciences, The University of Bath, Bath, A von,
BA27AY
V. Nascimento, Poultry Research Group, Department of Veterinary Anat
omy, Glasgow University Veterinary School, Bearsden Road, Glasgow,
G611QH
Contributors
S.E. Solomon, Poultry Research Group, Department of Veterinary Anatomy,
Glasgow University Veterinary School, Bearsden Road, Glasgow, G61
1QH
N.H.C. Sparks, Scottish Agricultural College, Poultry Science Department,
Auchincruive, Ayr, KA6 5HW
W J. Stadelman, Purdue University, Department of Food Science, 1160 Smith
Hall, West Lafayette, IN 47907-1160, USA
Preface
There is a marked and most unfortunate dichotomy in the studies of avian
eggs and hence in the application of new findings in commerce. Thus over
the past twenty years there has been a renewed interest in the contribu tions
of various parts of an egg to embryo development. This is best illustrated
by those studies that have explored the diffusion of respiratory gases across
the shell and at long last have provided a fundamental definition of a
previously nebulous term, porosity. The activity in this general area has led
in the past four years to the publication of three major books dealing with
many aspects of egg structure, function and embryogenesis. When brows
ing over these books, two developments are evident. First, the advantages
that are to be gained by comparative studies. Thus it is now common to see
within a single book articles concerned with the eggs of a range of avian
species as well as those of reptiles. Second, it is evident that zoologists and
physiologists as well as those employed in large breeding firms are all
contributing to an improvement of our knowledge of the egg's role in the
breeding biology of birds.
Comparative studies are a very uncommon feature of studies concerned
with bacterial infection of eggs. Moreover there is as yet little effort made
to link studies of bacterial contamination of eggs with a fundamental aspect
of eggs, the mechanisms allowing embryogenesis to occur without inter
ference from saprophytic microorganisms that could colonize the yolk and
deny the embryo its principal reserve of nutrients. Empirical observations
together with laboratory studies in the period 1900-1960 provided an
adequate basis for the mass production, distribution and marketing of eggs
without fear of a high incidence of addling. The inadequacies of these data
have been cruelly exposed by the current 'epidemic' of salmonellosis
associated with egg products. Indeed this book was prepared with the
objective of providing both an overview of current knowledge and a
platform upon which to build future studies. The editors wish to thank all
the contributors for their co-operation in producing this book.
Ron G. Board
Bath
Roy Fuller
Reading
Chapter One
Hen's egg shell structure and
function
S.B. SOLOMON, M.M. BAIN, S. CRANSTOUN
AND V. NASCIMENTO
The formation of the physical barrier to bacterial ingress into the egg takes
more than 20 h. During this time the yolk and albumen move from the
isthmus region of the oviduct, in which the paired shell membranes are
elaborated, to the tubular shell gland and shell gland pouch where miner
alization proceeds (Arias et al., 1993). The latter process is preceded by the
addition of plumping fluid to the albumen. This increases the total volume
of the latter and renders the flaccid shell membranes taut. Calcium salts
from the oviducal fluid in which the egg is bathed, precipitate onto selected
(nucleation) sites on the outer shell membrane. These sites are referred to
as the mammillary knobs and the whole as the mammillary layer. The true
shell consists of five morphologically distinct regions which, proceeding
outwards from and including the mammillary knob layer, are designated
the cone, palisade, vertical crystal layer and cuticle (Figure 1.1).
1.1 THE CUTICLE
Simons (1971) noted that cuticle thickness on the eggs of domestic hens
varies from 0.5 to 12.8 !lm over the surface of the same egg and has an
effective lifespan of 96 h after oviposition (Vadehra et al., 1970). The cuti
cle-less egg is not an unusual phenomenon (Sparks, 1985) and the patchy
distribution of cuticle, which Board and Halls (1973) reported on 8% of all
brown eggs studied in their experiments, is according to AIls et al. (1964)
the result of varying pressure within the shell gland pouch. (Figures 1.2-1.4)
The present authors propose that cuticular variation is the norm, with
age, strain and environment all exerting a profound effect on the degree of
cuticular coverage. Assessment of the latter using the dye 'Pea Green' is
both subjective and open to criticism as to its accuracy; thus eggs rendered
Microbiology of the Avian Egg. Edited by KG. Board and K Fuller. Published in 1994 by
Chapman & Hall, London. ISBN 041247570 7
