Fundamentals of Veterinary Microbiology (eBook)

Andrew N. Rycroft (Autor)

eBook Download: EPUB

2023
John Wiley & Sons (Verlag)
978-1-119-90836-4 (ISBN)

Infos

A compact and accessible guidebook exploring current understanding of common bacterial and fungal pathogens of animals. 
 
Fundamentals of Veterinary Microbiology brings together knowledge and understanding of the bacterial pathogens of animals from disease signs and diagnostic methods to the molecular basis of the host pathogen interaction.  A small but focused book, it enables the reader to access important information during diagnosis and treatment in a clinically relevant way.  Suitable as a companion for study on the subject and for professional use, the author focuses on the more clinically common diseases at the general and first-referral level.  
 
Divided into three sections, the first covers the basics of bacterial microbiology such as structure, growth and genetics. The second examines the commonly encountered bacterial pathogens, with emphasis on current understanding of the cellular and molecular basis of infection and immunity.  The third section explores the current state of knowledge of those fungi involved in infection of animals. 
Specific topics covered in Fundamentals of Veterinary Microbiology include: 
 

• Nutrition, sterilization, and disinfection of bacteria, bacterial genes and gene transfer, pathogenicity and host response, and vaccination 
• Antimicrobials (action, dynamics, and resistance), typing and identification of pathogens, fungi as agents of disease, Salmonella and E. coli in animal disease and public health. 
• Pathogens transmitted by vectors such as Borrelia, those of endogenous origin such as Clostridium and Pasteurella and those able to spread widely such as Leptospira, Mycobacterium and Chlamydia. 
• Fungal pathogens causing superficial, subcutaneous and systemic mycoses.  

Fundamentals of Veterinary Microbiology is an essential resource for veterinary students, veterinary nurses, and veterinary practitioners worldwide, allowing them to quickly establish a foundation of knowledge of bacterial pathogens based on clear understanding gained from studies over recent decades.  

The Author

Andrew N. RycroftBSc (Hons), PhD, FRCPath, is Emeritus Professor of Clinical and Veterinary Microbiology at the Royal Veterinary College, University of London, in the UK. He spent 9 years as lecturer at Glasgow University Veterinary School before moving to the RVC in 1992.  He is a fellow of the Royal College of Pathologists. 

Inhalt

Preface xvii

About the Companion Website xix

1 The Bacterial Cell 1

2 Metabolism, Growth and Culture of Bacteria 9

3 Sterilisation and Disinfection 15

4 Bacterial Genes and Gene Transfer 23

5 Bacterial Pathogenicity 29

6 Bacterial Veterinary Vaccines 39

7 Antimicrobials: Action, Dynamics and Resistance 43

8 Bacterial Typing 51

9 Salmonella 55

10 Escherichia coli - An Intestinal Pathogen 63

11 Escherichia coli as an Extraintestinal Pathogen 69

12 Campylobacter - Hyperendemic on the Farm 75

13 Leptospira - Using Urine to Spread 81

14 Lyme Disease - Ticks and Dogs 87

15 Brachyspira 91

16 Pasteurella 93

17 Pseudomonas and Burkholderia 97

18 Bordetella 101

19 Delicate Gram-negative Bacteria 105

20 Mannheimia, Actinobacillus and Other Pasteurellaceae 111

21 Chlamydia - A Stealthy Pathogen 117

22 Bovine Tuberculosis and Johne's Disease 121

23 Bacillus anthracis 129

24 Clostridium 133

25 Staphylococcus - Skin and Soft Tissue Infection 143

26 Streptococcus 149

27 Nocardia, Actinomyces and Dermatophilus - The Filamentous Pathogens 155

28 Prescottella (Rhodococcus) equi 159

29 Corynebacterium - CLA 163

30 Listeria - Growing in the Fridge 165

31 Erysipelothrix and Trueperella 169

32 Mycoplasma - Cell-associated Pathogens 173

33 Rickettsia - Arthropod Vector-borne Pathogens 179

34 Fungi as Agents of Disease 183

35 Aspergillus - Strength in Numbers 187

36 Dermatophytes - Keratinolytic Fungi 191

37 Yeasts: Malassezia, Candida and Cryptococcus 195

38 Dimorphic Fungal Infections 199

Index 205

Textauszug

1
The Bacterial Cell

Bacterial Structure

Bacteria are prokaryotic cells. The term ‘prokaryote’ includes the bacteria, the Archaea and blue‐green algae. The distinguishing feature of a prokaryote is that its nucleus is not surrounded by a nuclear membrane, but the nuclear material (DNA) is free in the cytoplasm of the cell. In addition, there is no nucleolus, mitotic spindle or (usually) any separate chromosomes. Bacterial cells are distinctively smaller in size than eukaryotic cells of plants, animals and fungi (Figures 1.1 and 1.2).

Shape

Individual bacteria have characteristic shapes. The cells may be spherical (coccus), rod shaped (bacillus), comma shaped (curved rod), spiral (spirochaete) or filamentous. Bacterial shape differs to some degree with the growth conditions (e.g. whether in the body or artificial medium of one kind or another). In some species, therefore, a bacterium may appear as long rods in lab culture, but as short rods or coccobacilli in the body when causing disease. Nevertheless, the shape of most bacteria can be seen in the light microscope and is an important clue to their identity (Figure 1.3).

Anatomy of the Bacterial Cell

The bacterial cell consists of the protoplast containing numerous organelles, which is bounded by a thin, elastic, semi‐permeable cytoplasmic membrane supported by the porous, relatively permeable rigid cell wall which bears a number of other structures (Figure 1.4).

Cytoplasmic Structures: Ribosomes, Nuclear Body

The cytoplasm is a gel containing organic and inorganic solutes, enzymes, ribosomes and the nucleic acids DNA and RNA. The ribosomes of prokaryotic cells are smaller than those of eukaryotic cells (plants, animals, fungi). They are known as 70S rather than the 80S ribosomes found in eukaryotic cells. This reflects a size difference because the Svedberg unit (S) is a unit of sedimentation and 80S ribosomes have a greater sedimentation rate than 70S. Both prokaryotic and eukaryotic ribosomes function to synthesise peptides (proteins), but they are sufficiently different organelles in the two groups for them to respond differently to inhibitors of protein synthesis such as some antibiotics which selectively disrupt the function of the ribosome.

The nuclear material (the DNA) is not a true nucleus. It is sometimes referred to as the nuclear body in bacteria because it is effectively free‐floating in the cytoplasm. Bacterial cells are haploid (one copy of each gene) and the DNA is arranged in a single closed circular molecule of about 1000 μm in length. The bacterial chromosome is not bound to protein histones as it is in eukaryotic cells, and it does not stain like a mammalian chromosome. In a section through a bacterial cell in the electron microscope, it appears as complex folds. Two or even four nuclear bodies may be seen in a bacterial cell as DNA replication and segregation occurs before cell division.

Figure 1.1 Bacterial cells stained by Gram stain and seen by light microscopy. The shape and arrangement are clear, but the resolution of the cells is limited by the light microscope.

Figure 1.2 Transmission electron microscope picture of a bacterial cell. The small granular organelles scattered throughout the cell are ribosomes; lighter regions are due to nuclear material.

Figure 1.3 Bacteria show different shapes: cocci, rods and curved rods.

Figure 1.4 Prototypic bacterial cell to show the common subcellular features.

Multiplication of bacteria is by simple growth and fission, not by mitosis. It is now recognised that bacteria have a cytoskeleton, which is needed for successful cell division. When a bacterial cell grows to sufficient size, the FtsZ protein forms a ring structure in the middle of the cell, known as the Z‐ring. This apparently constricts or contracts to make a pinch point or septum for cell division. FtsZ also acts to organise other cell division proteins at the site of septum formation, so it is likely to have a complex role. Other cytoskeletal proteins are necessary for positioning of the septum, involved in the shape of the bacterial cell and in the successful partitioning of the daughter chromosomes into separate ends of the cell following DNA replication (Egan et al. 2020).

The cytoplasmic membrane (or plasma membrane) limits the cytoplasm. It is a typical fluid‐mosaic model lipid bilayer about 9 nm across. It is composed of phospholipid and protein. The phospholipids are primarily phosphatidyl ethanolamine, with smaller proportions of phosphatidyl glycerol and cardiolipin (Figure 1.5).

Sterols are absent in almost all bacteria, but some Mycoplasma species, which have no cell wall, require sterols for growth and incorporate these into their membrane where they are essential for membrane stability. The membrane is flexible and is usually supported by a cell wall to maintain its integrity. The cytoplasmic membrane is the site of active transport via specific permease proteins. Its integrity is also essential for the maintenance of the proton gradient which is the driving force of electron transport and hence oxidative phosphorylation. Electron carriers of the respiratory chain, and ATPase, are located on the cytoplasmic membrane.

The Bacterial Cell Wall

The structures external to the cytoplasmic membrane constitute the bacterial envelope. One of these, the bacterial cell wall, provides the characteristic shape of the organism and prevents osmotic lysis of the cytoplasmic membrane. If the wall is ruptured, the cytoplasm expands through the gap and the cytoplasmic membrane bursts, killing the organism. This breakdown process is called lysis and can be caused by a number of agents: the enzyme lysozyme, some antibiotics, enzymes produced by bacteriophages (bacterial viruses) or enzymes produced by bacteria themselves (Figure 1.6).

Figure 1.5 The cytoplasmic membrane: phospholipid bilayer embedded with protein molecules.

When the cell wall is weakened or lost due to one of these agents in a situation where osmotic lysis does not occur (hypertonic solution), the shape of the organism may change. Spheroplasts (from Gram‐negatives) and protoplasts (from Gram‐positives) are formed. If bacteria lose their cell wall in vivo (in the body of an animal), they are known as L‐forms which may be a means by which some bacteria persist in the body during infection.

The cell wall of bacteria is a crucial structure as it is the site of action of some important groups of antimicrobials and the location of certain important antigens utilised both in identification of bacteria and in the immune response of the body to bacterial infection.

Figure 1.6 The cell wall peptidoglycan surrounds the cytoplasmic membrane as a tough sack‐like structure.

Peptidoglycan

Bacterial cell walls are quite different from those of eukaryotic cells, and they contain substances unique to bacteria. Peptidoglycan, formerly known as mucopeptide or murein, is the most important component of the cell wall. It is common to both Gram‐positive and Gram‐negative cells. It surrounds the cell, external to the cytoplasmic membrane, as a single bag‐like molecule. It is composed of linear glycan chains of alternating residues of N‐acetylglucosamine and N‐acetyl muramic acid. These are linked together by short peptide bridges to form a cross‐linked insoluble polymer (Rohs and Bernhardt 2021).

The peptide bridges vary between different organisms, but they are known to contain biologically exotic substances including meso‐diaminopimelic acid, D‐alanine and D‐glutamic acid. The peptidoglycan is a rigid structure which gives shape and strength to the bacterial cell wall.

Peptidoglycan forms the basic structure of the bacterial cell wall and similar peptidoglycan is found in the unconventional, obligate intracellular bacteria: Chlamydia and Rickettsia (Figure 1.7).

Figure 1.7 Peptidoglycan: long, linear glycan chains cross‐linked by short peptide bridges to form the tough cell wall polymer.

Figure 1.8 Simplified Gram‐positive cell envelope structure: thick peptidoglycan layer.

Figure 1.9 Simplified Gram‐negative cell envelope structure: thin peptidoglycan and a second membrane – the outer membrane.

In addition, other accessory polymers are also found in most bacteria. Gram‐positive organisms, such as staphylococci, contain teichoic acids composed of either poly‐glycerol phosphate or poly‐ribitol phosphate. These occur both within and on the surface of the cell wall and may account for 20–50% of the dry mass of the cell wall. On the streptococci, teichoic acids are sometimes the Lancefield group ‘carbohydrate’ antigens used in their classification and identification (Figure 1.8).

In Gram‐negative cells, the peptidoglycan is much thinner than in Gram‐positive organisms. Outside...

Produkt-Details

• Erscheint lt. Verlag: 2.11.2023
• Sprache: englisch
• Themenwelt: Veterinärmedizin ► Klinische Fächer ► Mikrobiologie / Immunologie
• Schlagworte: bacterial pathogens animals • host pathogen relationship animals • Mikrobiologie • mycoses, fungi in animal disease • pathogen diagnosis animals • pathogen immunity animals • pathogen research animals • pathogen transmission animals • pathogen vaccination animals • public health animal pathogens • Veterinärmedizin • Veterinärmedizin / Mikrobiologie,Parasitologie,Infektionen,Immunologie • Veterinary Medicine • Veterinary Microbiology, Parasitology,Infectious Diseases & Immunology
• ISBN-10: 1-119-90836-1 / 1119908361
• ISBN-13: 978-1-119-90836-4 / 9781119908364