Introduction To Microbiology

One can’t overemphasize the importance of microbiology.
Society benefits from microorganisms in many
ways. They are necessary for the production of bread,
cheese, beer, antibiotics, vaccines, vitamins, enzymes, and many
other important products. Indeed, modern biotechnology rests
upon a microbiological foundation. Microorganisms are indispensable
components of our ecosystem. They make possible the
cycles of carbon, oxygen, nitrogen, and sulfur that take place in
terrestrial and aquatic systems. They also are a source of nutrients
at the base of all ecological food chains and webs.
Of course microorganisms also have harmed humans and
disrupted society over the millennia. Microbial diseases undoubtedly
played a major role in historical events such as the decline of
the Roman Empire and the conquest of the New World. In 1347
plague or black death (see chapter 39) struck Europe with brutal
force. By 1351, only four years later, the plague had killed 1/3 of
the population (about 25 million people). Over the next 80 years,
the disease struck again and again, eventually wiping out 75% of
the European population. Some historians believe that this disaster
changed European culture and prepared the way for the Renaissance.
Today the struggle by microbiologists and others
against killers like AIDS and malaria continues. The biology of
AIDS and its impact (pp. 878–84)
In this introductory chapter the historical development of the
science of microbiology is described, and its relationship to medicine
and other areas of biology is considered. The nature of the microbial
world is then surveyed to provide a general idea of the organisms
and agents that microbiologists study. Finally, the scope,
relevance, and future of modern microbiology are discussed.
Microbiology often has been defined as the study of organisms and
agents too small to be seen clearly by the unaided eye—that is, the
study of microorganisms. Because objects less than about one millimeter
in diameter cannot be seen clearly and must be examined
with a microscope, microbiology is concerned primarily with organisms
and agents this small and smaller. Its subjects are viruses,
bacteria, many algae and fungi, and protozoa (see table 34.1). Yet
other members of these groups, particularly some of the algae
and fungi, are larger and quite visible. For example, bread molds
and filamentous algae are studied by microbiologists, yet are visible
to the naked eye. Two bacteria that are visible without a microscope,
Thiomargarita and Epulopiscium, also have been discovered
(see p. 45). The difficulty in setting the boundaries of
microbiology led Roger Stanier to suggest that the field be defined
not only in terms of the size of its subjects but also in term
of its techniques. A microbiologist usually first isolates a specific
microorganism from a population and then cultures it. Thus
microbiology employs techniques—such as sterilization and the
use of culture media—that are necessary for successful isolation
and growth of microorganisms.
The development of microbiology as a science is described
in the following sections. Table 1.1 presents a summary of some
of the major events in this process and their relationship to other
historical landmarks.
1.1 The Discovery of Microorganisms
Even before microorganisms were seen, some investigators suspected
their existence and responsibility for disease. Among
others, the Roman philosopher Lucretius (about 98–55 B.C.)
and the physician Girolamo Fracastoro (1478–1553) suggested
that disease was caused by invisible living creatures. The earliest
microscopic observations appear to have been made between
1625 and 1630 on bees and weevils by the Italian Francesco
Stelluti, using a microscope probably supplied by Galileo.
However, the first person to observe and describe microorganisms
accurately was the amateur microscopist Antony van
Leeuwenhoek (1632–1723) of Delft, Holland (figure 1.1a).
Leeuwenhoek earned his living as a draper and haberdasher (a
dealer in men’s clothing and accessories), but spent much of his
spare time constructing simple microscopes composed of double
convex glass lenses held between two silver plates (figure
1.1b). His microscopes could magnify around 50 to 300 times,
and he may have illuminated his liquid specimens by placing
them between two pieces of glass and shining light on them at a
45° angle to the specimen plane. This would have provided a
form of dark-field illumination (see chapter 2) and made bacteria
clearly visible (figure 1.1c). Beginning in 1673 Leeuwenhoek
sent detailed letters describing his discoveries to the Royal
Society of London. It is clear from his descriptions that he saw
both bacteria and protozoa.
1.2 The Conflict over Spontaneous Generation
From earliest times, people had believed in spontaneous
generation—that living organisms could develop from nonliving
matter. Even the great Aristotle (384–322 B.C.) thought some
of the simpler invertebrates could arise by spontaneous generation.
This view finally was challenged by the Italian physician
Francesco Redi (1626–1697), who carried out a series of experiments
on decaying meat and its ability to produce maggots
spontaneously. Redi placed meat in three containers. One was
uncovered, a second was covered with paper, and the third was
covered with a fine gauze that would exclude flies. Flies laid
their eggs on the uncovered meat and maggots developed. The
other two pieces of meat did not produce maggots spontaneously.
However, flies were attracted to the gauze-covered container and
laid their eggs on the gauze; these eggs produced maggots.