Veterinary Microbiology and Microbial Disease

479 Pages·2001·54.39 MB·English

by  P. J. Quinn

Contents
Preface vi 26. Bordetella bronchiseptica
Acknowledgements vi and Bordetella avium
Author biographies vii 27. Moraxella bovis
28. Brucella species
29. Campylobacter species
Section I
30. Lawsonia intracellularis
Introductory Bacteriology
31. Spirochaetes
Microbial pathogens and infectious 32. Pathogenic anaerobic non-spore-
disease forming Gram-negative bacteria
Structure of bacterial cells 33. Mycoplasmas
Cultivation, preservation and 34. Chlamydia and Chlamydophila
inactivation of bacteria species
Bacterial genetics and mechanisms 35. Rickettsiales
of genetic variation 36. Bacterial species of limited
Laboratory diagnosis of pathogenic significance
bacterial disease
Antimicrobial agents
Section I11
Bacterial colonization, tissue
Mycology
invasion and clinical disease
37. General features of fungi associated
with disease in animals
Section I1
38. Dermatophytes
Pathogenic Bacteria
39. Aspergillus species
8. StaphyIococcus species 40. Yeasts and disease production
9. Streptococci 41. Dimorphic fungi
10. Corynebacterium species 42. Zygomycetes of veterinary
11. Rhodococcus equi importance
12. Actinomycetes 43. Fungus-like organisms of veterinary
13. Listeria species importance
14. Erysipelothrix rhusiopathiae 44. Pneumocystis carinii
15. Bacillus species 45. Opportunistic infections caused
16. Clostridium species predominantly by phaeoid fungi
17. Mycobacterium species 46. Mycotoxins and mycotoxicoses
18. Enterobacteriaceae 47. Pathogenic algae and cyanobacteria
19. Pseudomonas aeruginosa and
Burkholderia species
Section IV
20. Aeromonas species, Plesiomonas
Introductory Virology
shigelloides and Vibrio species
21. Actinobacillus species 48. Nature, structure and taxonomy
22. Pasteurella species and of viruses
Mannheimia haemolytica 49. Replication of viruses
23. Francisella tularensis 50. Genetics and evolution of viruses
24. Haemophilus species 51. Propagation of viruses and
25. Taylorella equigenitalis virus-cell interactions
iv Veterinary Microbiology and Microbial Disease
52. Pathogenesis of viral diseases 301 74. Flaviviridae 426
53. Laboratory diagnosis of viral 75. Togaviridae 434
infections 305 76. Prions: unconventional infectious
agents 43 8
Section V
Viruses and Prions Section VI
Microbial Agents and Disease Production
54. Herpesviridae
55. Papillomaviridae 77. Interactions of microbial pathogens
56. Adenoviridae with the nervous system
57. Poxviridae 78. Interactions of microbial pathogens
58. Asfarviridae with the male and female
59. Parvoviridae reproductive systems
60. Circoviridae 79. The role of microbial pathogens
61. Retroviridae in intestinal disease
62. Reoviridae 80. Microbial infections and
63. Birnaviridae pneumonia
64. Orthomyxoviridae 81. Bacterial causes of bovine
65. Paramyxoviridae mastitis
66. Rhabdoviridae 82. Foot infections of cattle, sheep
67. Bornaviridae and pigs associated with
68. Bunyaviridae microbial agents
69. Picornaviridae 83. Disinfection and other aspects of
70. Caliciviridae disease control
71. Astroviridae 84. Infection and immunity
72. Coronaviridae
73. Arteriviridae Index 517
Section I
Introductory Bacteriology
Chapter 1
Microbial pathogens and infectious disease
Although the concept of infectious diseases is to be found showed that a contaminating yeast, which produced lactic
in the works of classical Greek and Roman writers, their acid during fermentation and which differed morphologi-
microbial aetiology was not clearly established until the cally from brewers' yeast, was responsible for the
mid-nineteenth century when it was confirmed by the sci- spoilage. He deduced that both alcoholic and lactic
entific contributions of Louis Pasteur and Robert Koch. fermentation resulted from the metabolism and replication
During the intervening centuries a number of investigators of the living yeast cells. The solution to the spoilage
hypothesized about the nature of contagion and disease. problem during fermentation of wine and beer products,
Girolamo Fracastoro was one of the first to suggest, in his lay in heating the raw materials to about 120"F, in order to
treatise De contagione published in 1546, that animate kill contaminating microorganisms, prior to the addition of
agents were responsible for disease. One hundred years the appropriate yeast cells. This process, now known as
later, Anthony van Leeuwenhoek demonstrated, in a pasteurization, is widely used to reduce microbial contami-
sample of pus from his gums, microscopic 'animalcules', nation in order to prolong the shelf-life of milk and some
which were later identified as infectious agents. other foods.
For many centuries there had been philosophical and Pasteur effectively ended the controversy about
scientific discussion about the 'spontaneous generation' of spontaneous generation through definitive confirmation of
small living entities. One of the most persuasive naked- Spallanzani's experiments. Furthermore, he demonstrated
eye observations which supported spontaneous generation, that contamination of nutrient broth when exposed to air
namely the occurrence of maggots on putrefying meat, had resulted from microorganisms in dust particles settling on
been put to rest by the experiments of Francesco Redi the fluid.
(1626-1697) an Italian physician and naturalist. He An important technical advance, which stemmed from
demonstrated that maggots developed in meat only when Pasteur's fermentation studies, was the development of a
flies laid their eggs on it. However, van Leeuwenhoek's fluid medium suitable for culturing yeast cells. He then
confirmation of the existence of microscopic 'animalcules' developed other liquid media containing specific ingredi-
meant that the question of spontaneous generation ents which favoured the growth of particular pathogenic
remained unresolved. The concept was apparently bacteria. It was this development which eventually
supported by experiments conducted in the mid-eighteenth allowed him to formulate the germ theory of disease. The
century by John Needham, an English naturalist. After germ theory formed the basis for Pasteur's experiments on
boiling broth in containers which were then sealed, vaccination against fowl cholera, anthrax and rabies. An
Needham detected microorganisms in the broth when the additional practical application of the theory was the
containers were opened after a few days. Subsequently, introduction of phenol as a disinfectant for surgical
Needham's experimental technique was shown to bc procedures by the British surgeon Joseph Lister.
faulty. Boiling for a short time failed to eliminate all the Together with Pasteur, the German physician Robert
microorganisms from the broth and the containers; an Koch is considered to be a cofounder of modern
extended period of boiling was essential. When the broth microbiology. Having observed bacilli in the blood of ani-
was boiled for periods approaching three quarters of an mals which had died from anthrax, Koch demonstrated
hour and the flasks sealed immediately after boiling, their pathogenicity by injecting mice with the blood. The
microorganisms were not demonstrable even after injected mice died and the bacilli were present in prepara-
prolonged storage. Despite these exacting experiments tions from their swollen spleens. He was also able to
which were carried out by Lazzaro Spallanzani, transfer the infection from mouse to mouse and to demon-
protagonists of spontaneous generation continued to pro- strate the bacilli in each newly infected mouse. Initially,
mote the concept up to the mid-1800s when Louis Pasteur Koch used blood serum for growing the anthrax bacillus in
became involved in biological investigations. vitro. Later, he developed solid media which allowed
Pasteur's interest in spontaneous generation was isolation of individual bacterial colonies. Using a solid
prompted by experiments which he had conducted on medium, he was eventually able to isolate the tubercle
spoilage during the fermentation of beet alcohol. He bacillus from the tissues of an experimental animal in
4 Veterinary Microbi 'ology and Microbial Disease
which he had demonstrated microscopically the presence Table 1.1 Comparative features of prokaryotic and eukaryotic
of the organism. As a result of these observations, Koch cells.
formulated certain principles for proving that a specific
microorganism caused a particular disease: the specific
Prokaryotic cell Eukaryotic cell
microorganism must be present in all affected animals and
after isolation in vitro, must cause the disease when Usually less than 5pm in Usually more than 10 pm in
inoculated into susceptible animals. The identical length diameter
microorganism must then be isolated from the inoculated
Membrane-boundo rganelles Membrane-boundo rganelles
animals. absent present
Pasteur's germ theory of disease and Koch's postulates
70s ribosomes 80s ribosomes in cytoplasm;
are the two corner-stones on which microbiology is based
70s ribosomes in mitochondria
and without which, this branch of biology could not have
and chloroplasts
advanced. During the past century, major developments
have taken place in microbiological concepts, techniques Nucleic acid occurs as a single Nucleic acid is distributed in
molecule, often circular chromosomes
and applications. Modern microbiology encompasses the
study of bacteria, fungi, viruses and other microscopic and Nuclear membrane and Nuclear membrane and
submicroscopic organisms (Box 1.1). In veterinary micro- nucleolus absent nucleolus present
biology, emphasis is placed on those microorganisms
Replicate by binary fission Replicate by mitosis
associated with infectious diseases of animals.
Immunology, the study of host responses to infectious
agents, is a discipline closely related to microbiology and second branch (Fig. 1.1). Lateral as well as horizontal
is sometimes considered as a distinct but cognate subject. transfer of genetic material probably occurred in the course
Living cells, the smallest units capable of independent of evolutionary development, with some eubacterial genes
existence, can be divided into two sharply differentiated incorporated into members of the Archaebacteria and
groups, eukaryotes and prokaryotes. The main differenti- perhaps with some prokaryotic genes incorporated into
ating features of eukaryotic and prokaryotic cells are eukaryotes. This lateral gene transfer may explain how
presented in Table 1.1. Eukaryotes possess true nuclei complex eukaryotic cells acquired some of their genes and
which contain chromosomes and individual cells replicate organelles. The endosymbiosis hypothesis proposes that,
by mitosis. In addition, a typical eukaryotic cell contains at some stage in their early development, eukaryotic cells
organelles such as mitochondria, a Golgi apparatus, became primitive phagocytes and acquired particular
lysosomes and relatively large ribosomes. Organisms in bacterial cell types which enhanced their respiratory
the Archaebacteria and Eubacteria, which are less complex activity (de Duve, 1996). It is proposed that the engulfed
than eukaryotic organisms, are prokaryotes which lack true bacteria provided extra energy through this enhanced
membrane-bound nuclei. Their genetic information is respiration to the host cell and eventually evolved into
contained in a single circular chromosome. In some mitochondria. A similar phenomenon may account for the
prokaryotic cells such as bacteria, extrachromosomal development of chloroplasts in plant cells. The
DNA, in the form of plasmids, encodes for certain charac- cytoplasmic membrane is the site of respiratory or
teristics of the organism. Although the origin of life is a photosynthetic energy-generation in prokaryotes unlike
much debated subject, it is probable that primitive eukaryotes, in which these activities occur in the
microorganisms originated from ancestral life forms membranes of mitochondria and chloroplasts.
several billion years ago (Fig. 1.1). The degree of related-
ness among microorganisms can be assessed by
Pathogenic microorganisms
comparison of their ribosomal ribonucleic acid (rRNA).
There is some evidence that all organisms developed from Most microorganisms found in nature are not harmful
a group of primitive cells rather than from a single to humans, animals or plants. Indeed, many bacteria and
organism (Doolittle, 1999). Prokaryotcs are considered as fungi make an important contribution to biological
one branch of the phylogenetic tree and eukaryotes as the activities which take place in soil, in water and in the
alimentary tract of animals. Those microorganisms which
can cause disease in animals or humans are referred to as
Box 1.1 Subdivisions of microbiology.
pathogenic microorganisms.
Bacteriology, the study of bacteria
Bacteria
Mycology, the study of fungi
Microorganisms belonging to the Archaebacteria are not
Virology, the study of viruses
associated with diseases of domestic animals. Organisms
The study of unconventional infectious
(bacteria) belonging to the Eubacteria include many
agents including prions
pathogens of veterinary importance.
Microbial pathogens and infectious disease 5
Figure 1.1 The evolutionary relationships of living organisms. Endosymbiosis is the postulated mechanism whereby eukaryotic cells
acquired mitochondria or chloroplasts by incorporation of prokaryotic cells.
Bacteria are unicellular and are smaller and less growth. Two groups of small bacteria, rickettsiae and
complex than eukaryotic cells such as mammalian red chlamydiae, which are unable to multiply on inert media,
blood cells (Table 1.2). They usually have rigid cell walls require living cells for in vitro growth. Cyanobacteria,
containing a peptidoglycan layer, multiply by binary formerly referred to as blue-green algae, utilize chloro-
fission and exhibit considerable morphological diversity. phyll for some metabolic pathways. Unlike algae, which
They occur as rods, cocci, helical forms and occasionally store chlorophyll in organelles referred to as chloroplasts,
as branching filaments. Despite their morphological cyanobacteria have chlorophyll distributed inside their cell
diversity, most bacteria are between 0.5 pm and 5 pm in membranes.
length. Motile bacteria possess flagella by which they can
movk through liquid media. The majority of bacteria can Fungi
grow on suitable inert media; some require special growth Yeasts, moulds and mushrooms belong to a large group of
supplements and particular atmospheric conditions for non-photosynthetic eukaryotes, termed fdngi. Fungi may
be either unicellular or multicellular. Multicellular fungi
produce filamentous microscopic structures called moulds;
Table 1.2 A comparison of the morphology and size of bacterial yeasts which are unicellular, have a spherical or ovoid
cells relative to a mammalian red blood cell. shape and multiply by budding. In moulds the cells are
cylindrical and attached end-to-end, forming branched
hyphae (Table 1.3). A notable feature of fungi is their
Cell Morphology/size Comments
ability to secrete potent enzymes which can digest organic
matter. When moisturc is present and other environmental
Red blood cell Readily seen using conditions are favourable, fungi can degrade a wide variety
conventional light microscopy
of organic substrates. A small number of yeasts and
7 C L ~ moulds are pathogenic for humans and animals. Some
fungi invade tissues whereas others produce toxic
Bacillus 0 Rod-shaped cells, usually substances called mycotoxins which, if present on crops or
stained by the Gram method. in stored food such as grain or nuts, can cause disease in
5 Clm Using bright-field microscopy,
a magnification of I ,000is~ animals and humans.
required to observe most
bacterial cells.
Algae
Coccus 0 Spherical-shaped Often A morphologically and physiologically diverse group of
occuring in chains or in grape-
1 Pm like clusters organisms, algae, are usually considered plant-like because
they contain chlorophyll. Many algae are free-living in
Splrochaete Thin, helical bacteria ~ ~ ~ k - f ~ ~ l d
microscopy (without staining) water; others grow on the surfaces of rocks and on other
10 Cml
structures in the environment. Some algae produce
~ ~ ~ ~ ~ $ ~ , " t ~ , " ~ ~ $ $ ~ , " ~ ~ , " ~ ~
unusual microorganisms. pigments which impart distinct colouration to water
6 Veterinary Microbiology and Microbial Disease
Table 1.3 A comparison of the morphology and size of a induced changes, structurally altered abnormal protein
bacterial cell and two fungal forms. accumulates in and damages long-lived cells such as
neurons. Genetic factors seem to influence the
Structure Morpholopy/size Comments susceptibility of humans and animals to prion diseases.
Prions exhibit remarkable resistance to physical and
Bacterial cell
chemical inactivation procedures.
Coccus 0 Often occur in chains or grape-
like clusters
1 um
Biological classification and nomenclature
Fungal forms
Microscopic living organisms were formerly classified on
0
Yeast Reproduce by buddtng the basis of phenotypic expression including morphology
and distinct attributes reflecting unique metabolic
properties. Increasingly, classification methods for
microorganisms have come to rely heavily on genotypic
analysis. In recent years, this has led to changes in the
classification and nomenclature of microorganisms.
Mould Branched structures (hyphae) Species are groups of organisms with similar genetic
composed of many cells
and metabolic characteristics. Closely related species are
initially grouped into genera and thereafter into families,
orders, classes, phyla and kingdoms (Box 1.2). Organisms
are usually referred to by their generic and specific names,
surfaces containing algal blooms. When water tempera- for example, the bacterium which causes anthrax in
tures are high, algal growth may be marked, leading to the humans and animals is termed Bacillus anthracis, Bacillus
production of toxins which can accumulate in shellfish or being the generic name and anthracis the specific name.
in water containing algal blooms. This binomial system of nomenclature was devised in the
eighteenth century by the Swedish naturalist, Linnaeus.
Viruses Viruses are not classified according to the Linnaean
Unlike bacteria and fungi, viruses are not cells. A virus system because they are not cells and cannot reproduce
particle or virion consists of nucleic acid, either DNA or independently. They are generally grouped in families
RNA, enclosed in a protein coat called a capsid. In based on virion morphology and nucleic acid type. Further
addition, some viruses are surrounded by an envelope. subdivision of pathogenic animal viruses relates to the
Viruses are much smaller than bacteria, and range in size species of host affected and to the clinical disease which is
.
from 20 nm to 300 nm in diameter (Table 1.4). Despite produced.
their simple structure, viruses occur in many shapes.
Some are spherical, others are brick and bullet-shaped and
a few have an elongated appearance. Because they lack
Table 1.4 A comparison of a bacterial cell and a large and a
the structures and enzymes necessary for metabolism and
small virusa.
independent reproduction, viruses can multiply only within
living cells. Both prokaryotic and eukaryotic cells are
susceptible to infection by viruses. Those viruses which Stmctum Morphology/size Comments
invade bacterial cells are called bacteriophages.
Pathogenic viruses which infect humans and animals can
cause serious disease by invading and destroying cells. A
small number of viruses are aetiologically implicated in
the development of malignant tumours in humans and
animals.
Prions
Viruses Viruses cannot be seen
Infectious particles which are smaller than viruses, have using conventional bright-
been implicated in the neurological diseases of animals Poxvirus field microscopy. Electron
microscopy at a
kidr6umans termed transmissible spongiform magnification of up to
ncephalopathies. These particles, called prions, are 300 nm 100,000~is used to
demonstrate viruses in
!i stinct from viruses and appear to be devoid of nucleic pawovirus 8 clinical specimens or in
ackk, Prions seem to be composed of an abnormally folded 20 nm laboratory preparations.
prbtein capable of inducing conformational changes in
corresponding normal host cell protein. Following the a not drawn to scale
/ / ('i
Microbial pathogen:P and infectious disease 7
Table 1.6 Units of measurement used in microbiology.
Box 1.2 Categories used for the taxonomic
classification of microorganisms.
Unit Abbreviation Comments
Kingdom (includes all microorganisms)
-Phylum (group of related classes in kingdom) Millimetre mm One thousandth of a metre ( 1 ~m3).
-Class (group of related orders in phylum) Bacterial and fungal colony sizes are
usually measured in mm. When
-Order (group of related families in class)
growing on a suitable medium,
-Family (group of related genera in order)
bacterial colonies range in size from
-Genus (group of related species in family) 0.5 mm to 5 mm
-Species (organisms with similar features)
Micrometre pm One thousandth of a millimetre
(micron) (10-6 m). Used for the size of
Microscopical techniques bacterial and fungal cells. Most
bacteria range in size from 0.5 pm to
A number of different microscopic methods are employed 5 prn. A small number of bacteria
for examining microorganisms. These include bright-field, may exceed 20 pm in length
dark-field, phase contrast and electron microscopy. Table
Nanometre nm One thousandth of a micrometre
1.5 summ~rizesc ommon staining methods used in (10-9 m). Used for expressing the
microscopy and the particular types of microorganisms for size of viruses. Most viruses of
which the techniques are appropriate. Units of measure- veterinary importance range in size
from 20 nm to 300 nm
ment employed in microscopy are indicated in Table 1.6.
The maximum magnification obtainable by bright-field
microscopy, using oil-immersion objectives, is approxi-
mately 1000~.W ith bright-field microscopy, suitably
stained bacteria as small as 0.2 pm in size can be unstained specimens. This procedure is more appropriate
visualized. With dark-field microscopy, the scattering of for research purposes than for routine diagnostic
light by fine microorganisms such as spirochaetes microbiology.
suspended in liquid allows them to be observed against a In transmission electron microscopy, beams of electrons
dark background. In common with dark-field techniques, are used in place of visible light to visualize small
phase-contrast microscopy can be used to examine structures such as viruses. Specimens, placed on grids, are
negatively stained with electron-dense compounds such as
potassium phosphotungstate and viewed as magnified
images on a fluorescent screen. Magnifications greater
Table 1.5 Microscopical techniques used in microbiology.
than 100,000~a re possible with modern instruments.
Scanning electron microscopy is used to obtain three-
Technique Comments dimensional views of microorganisms when coated with a
thin film of heavy metal. With this technique, a wide
Bright-field Used for demonstrating the morphology and
range of magnifications up to 100,000~is feasible.
microscopy size of stained bacteria and fungi; staining
affinity may allow preliminary classification of
bacteria and the morphology of fungal
References
structures permits identification of the genus
de Duve, C. (1996). The birth of complex cells. Scientific
Phase-contrast Used for examining unstained cells in
microscopy suspension American, 274,3845,
Doolittle, W.F. (1999). Phylogenetic classification and the uni-
versal tree. Science, 284, 2124-2128.
Dark-field Used for examining unstained bacteria such
microscopy as spirochaetes in suspension
Further reading
Fluorescent Used for identifying microorganisms with
microscopy specific antibodies conjugated with
DebrC, P. (1998). Louis Pasteur. Johns Hopkins University
fluorochromes
Press Ltd., London.
'
Transmission Used for demonstrating viruses in biological Lechevalier, H.A. and Solotorovsky, M. (1965). Three Centuries
electron material and for identifying ultrastructural
ofMicrobiology. McGraw-Hill Book Company, New York.
microscopy details of bacterial, fungal and mammalian
Madigan, M.T., Martinko, J.M. and Parker, J. (1997). Brock
cells
Biology of Microorganisms. Eighth Edition. Preqtice Hall
Scanning Used for demonstrating the three-dimensional International, London.
electron structure of microorganisms
Schlegel, H.G. (1993). General Microbiology. Seventh Edition.
microscopy
Cambridge University Press, Cambridge.
Chapter 2
The structure of bacterial cells
A typical bacterial cell is composed of a capsule, cell wall, Table 2.1 Structural components of bacterial cells.
cell membrane, cytoplasm containing nuclear material and
appendages such as flagella and pili (fimbriae). Certain
species of bacteria can produce forms termed spores or Chemical
Structure Comments
composition
endospores, which are resistant to environmental
influences. Some of the structural features of pathogenic
Capsule Usually poly- Often associated with
bacteria which are important in the production of disease
saccharide; virulence; interferes with
or may be useful for the laboratory diagnosis of infection polypeptide in phagocytosis; may prolong
are reviewed in Chapters 5 and 7. The principal structural Bacillus anthracis survival in the environment
components of bacterial cells are presented in Table 2.1.
Cell wall Peptidoglycan and Peptidoglycan is responsible
teichoic acid in for the shape of the
Capsule Gram-positive organism. LPS is
bacteria. responsible for endotoxic
Bacteria can synthesize extracellular polymeric material Lipopolysacch- effects. Porins, protein
aride (LPS), structures, regulate the
which is usually described as glycocalyx. In some
protein, phospho- passage of small molecules
bacterial species this polymeric material forms a capsule, a
lipid and peptido- through the phospholipid
well-defined structure closely adherent to the cell wall. A glycan in Gram- layer.
slime layer is formed when the polymeric material is negative bacteria
present as a loose meshwork of fibrils around the cell.
Most capsules are composed of polysaccharides; Bacillus Cytoplasmic Phospholipid Selectively permeable
membrane bilaver membrane involved in active
species such as B. anthracis produce polypeptide capsules.
transport of nutrients,
Defined capsules can be visualized by light microscopy
respiration, excretion and
using negative staining techniques. Bacteria with well- chemoreception.
defined capsular material produce mucoid colonies on agar
media. However, the capsules of most species of bacteria Flagellum Protein called Filamentous structure which
can be demonstrated only by electron microscopy or by (plural, flagellin confers motility
flagella)
immunological methods using antisera specific for the
capsular (K) antigens. The main function of capsular
Pilus (plural, Protein called pilin Also known as fimbria (plural,
material appears to be protection of the bacterium from pili) ' fimbriae). Thin, straight,
adverse environmental conditions such as desiccation. In thread-like structures present
on many Gram-negative
the body, capsules of pathogenic bacteria may facilitate
bacteria. Two types exist,
adherence to surfaces and interfere with phagocytosis.
attachment pili and
conjugation pili.
Cell wall
Chromosome DNA Single circular structure with
The tough, rigid cell walls of bacteria protect them from no nuclear membrane
mechanical damage and osmotic lysis. As cell walls are
Ribosome RNA and protein Involved in protein synthesis
non-selectively permeable, they exclude only very large
molecules. Differences in the structure and chemical
Storage Chemical Present in some bacterial
composition of the cell walls of bacterial species account granules or composition cells; may be composed of
for variation in their pathogenicity and influence other inclusions variable polyphosphate (volutin or
metachromatic granules),
characteristics including staining properties.
poly-beta-hydroxybutyrate
Peptidoglycan, a polymer unique to prokaryotic cells,
(reserve energy source),
' imparts rigidity to the cell wall. This polymer is composed glycogen
of chains of alternating subunits of N-acetylglucosamine