Essential Microbiology

Stuart Hogg

• Publisher: Wiley-Blackwell
• Year: 2013
• ISBN:
  9781118527269
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Microbiology
• Index: Biological Sciences

Essential Microbiology 2nd Edition is a fully revised comprehensive introductory text aimed at students taking a first course in the subject. It provides an ideal entry into the world of microorganisms, considering all aspects of their biology (structure, metabolism, genetics), and illustrates the remarkable diversity of microbial life by devoting a chapter to each of the main taxonomic groupings. The second part of the book introduces the reader to aspects of applied microbiology, exploring the involvement of microorganisms in areas as diverse as food and drink production, genetic engineering, global recycling systems and infectious disease. Essential Microbiology explains the key points of each topic but avoids overburdening the student with unnecessary detail. Now in full colour it makes extensive use of clear line diagrams to clarify sometimes difficult concepts or mechanisms. A companion web site includes further material including MCQs, enabling the student to assess their understanding of the main concepts that have been covered.

This edition has been fully revised and updated to reflect the developments that have occurred in recent years and includes a completely new section devoted to medical microbiology. Students of any life science degree course will find this a concise and valuable introduction to microbiology.

I

Introduction

1

Microbiology: What, Why and How?

Microorganisms (or microbes) inhabit every corner of the globe, and are essential for the maintenance of the world's ecosystems. They include organisms responsible for some of the most deadly human diseases, and others that form the basis of important industrial processes. Yet until a few hundred years ago, nobody knew they existed! This book offers an introduction to the world of microorganisms, and in this opening chapter, we offer some answers to three questions:

• What is microbiology?
• Why is it such an important subject?
• How have we gained our present knowledge of microbiology?

1.1 What is microbiology?

Things aren't always the way they seem. On the face of it, ‘microbiology’ should be an easy word to define: the science (logos) of small (micro) life (bios), or to put it another way, the study of living things so small that they can't be seen with the naked eye. Bacteria neatly fit this definition, but what about fungi and algae? These two groups each contain members that are far from microscopic. On the other hand, certain animals, such as nematode worms, can be microscopic, yet are not considered to be the domain of the microbiologist. Viruses represent another special case; they are most certainly microscopic; indeed, most are submicroscopic, but by most accepted definitions they are not living (why? – see Chapter 10 for an explanation). Nevertheless, these too fall within the remit of the microbiologist.

In the central section of this book you can read about the thorny issue of microbial classification and gain some understanding of just what is and what is not regarded as a microorganism.

1.2 Why is microbiology important?

To the lay person, microbiology means the study of sinister, invisible ‘bugs’ that cause disease. As a subject, it generally tends to impinge on the popular consciousness in news coverage concerning the latest ‘health scare’. It may come as something of a surprise therefore to learn that the vast majority of microorganisms coexist alongside us without causing any harm; indeed, at least a thousand different species of bacteria are to be found on human skin! In addition, many microorganisms are positively beneficial, performing vital tasks such as the recycling of essential elements, without which life on our planet could not continue, as we'll examine in Chapter 14. Other microorganisms have been exploited by humans for our own benefit, for instance in the manufacture of antibiotics (Chapter 17) and foodstuffs (Chapter 18). To get some idea of the importance of microbiology in the world today, just consider the following list of some of the general areas in which the expertise of a microbiologist might be used:

• medicine
• environmental science
• food and drink production
• fundamental research
• agriculture
• pharmaceutical industry
• genetic engineering

The popular perception among the general public, however, remains one of infections and plagues. Think back to the first time you ever heard about microorganisms; almost certainly, it was when you were a child and your parents impressed on you the dangers of ingesting ‘germs’ from dirty hands or putting things in your mouth after they'd been on the floor. In reality, only a couple of hundred out of the half million or so known bacterial species give rise to infections in humans; these are termed pathogens, and have tended to dominate our view of the microbial world.

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A pathogen is an organism with the potential to cause disease.

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In the next few pages we shall review some of the landmark developments in the history of microbiology, and see how the main driving force throughout this time, but particularly in the early days, has been the desire to understand the nature and cause of infectious diseases in humans.

1.3 How do we know? Microbiology in perspective: to the Golden Age and beyond

We have learnt an astonishing amount about the invisible world of microorganisms, particularly over the last century and a half. How has this happened? The penetrating insights of brilliant individuals are rightly celebrated, but a great many ‘breakthroughs’ or ‘discoveries’ have only been made possible thanks to some (frequently unsung) development in microbiological methodology. For example, on the basis that ‘seeing is believing’, it was only when we had the means to see microorganisms under a microscope that we could prove their existence.

Microorganisms had been on the Earth for some 4000 million years when Antoni van Leeuwenhoek started his pioneering microscope work in 1673. Leeuwenhoek was an amateur scientist who spent much of his spare time grinding glass lenses to produce simple microscopes (Figure 1.1). His detailed drawings make it clear that the ‘animalcules’ he observed from a variety of sources included representatives of what later became known as protozoa, bacteria and fungi. Where did these creatures come from? Arguments about the origin of living things revolved around the long-held belief in spontaneous generation, the idea that living organisms could arise from non-living matter. In an elegant experiment, the Italian Francesco Redi (1626–1697) showed that the larvae found on putrefying meat arose from eggs deposited by flies, and not spontaneously as a result of the decay process. This can be seen as the beginning of the end for the spontaneous generation theory, but many still clung to the idea, claiming that while it may not have been true for larger organisms, it must surely be so for minute creatures such as those demonstrated by Leeuwenhoek. Despite mounting evidence against the theory, as late as 1859 fresh ‘proof’ was still being brought forward in its support. Enter onto the scene Louis Pasteur (1822–95), still arguably the most famous figure in the history of microbiology. Pasteur trained as a chemist, and made a lasting contribution to the science of stereochemistry before turning his attention to spoilage problems in the wine industry. He noticed that when lactic acid was produced instead of alcohol in wine, rod-shaped bacteria were always present as well as the expected yeast cells. This led him to believe that while the yeast produced the alcohol, the bacteria were responsible for the spoilage, and must have originated in the environment. Exasperated by continued efforts to substantiate the theory of spontaneous generation, he set out to disprove it once and for all. In response to a call from the French Academy of Science, he carried out a series of experiments that led to the acceptance of biogenesis, the idea that life arises only from already existing life. Using his famous swan-necked flasks (Figure 1.2), he demonstrated that as long as dust particles (and the microorganisms carried on them) were excluded, the contents would remain sterile. This also disproved the idea held by many that there was some element in the air itself that was capable of initiating microbial growth. In Pasteur's words ‘….the doctrine of spontaneous generation will never recover from this mortal blow. There is no known circumstance in which it can be affirmed that microscopic beings came into the world without germs, without par...