MICROBIOLOGY – BACTERIOLOGY
Microbiology
is study of organisms of microscopic size,
including bacteria, protozoans, viruses, and certain algae and fungi.
Bacteriology is study of bacteria, including their classification
and the prevention of diseases that arise from bacterial infection. The subject
matter of bacteriology is distributed not only among bacteriologists but also
among chemists, biochemists, geneticists, pathologists, immunologists, and
doctors.
Bacteria were first
observed by the Dutch naturalist Anton
van Leeuwenhoek with the aid of a simple microscope of his own
construction. He reported his discovery to the Royal Society of London in 1683,
but the science of bacteriology was not firmly established until the middle of
the 19th century. For nearly 200 years it was believed that bacteria
are produced by spontaneous generation. The efforts of several generations of
chemists and biologists were required to prove that bacteria, like all living
organisms, arise only from other similar organisms. This fundamental fact was
finally established in 1860 by the French scientist Louis Pasteur, who also discovered that the process of fermentation
and many infectious diseases are caused by bacteria. The first systematic
classification of bacteria was published in 1872 by the German biologist Ferdinand J. Cohn, who placed them in
the plant kingdom. They are now usually included in the kingdom Monera. In 1876
Robert Koch, who had devised the
method of inoculating bacteria directly into nutrient media as a means of
studying them, found that a bacterium was the cause of the disease anthrax.
Since 1880, immunity
against bacterial diseases has been systematically studied. In that year,
Pasteur discovered by accident that Bacillus anthracis, cultivated at a
temperature of 42° to 43° C, lost its virulence after a few generations. Later
it was found that animals inoculated with these enfeebled bacteria showed
resistance to the virulent bacilli. The prevention, modification, and treatment
of disease by immunization, one of the most important modern medical advances,
date from this beginning.
Other significant
developments in bacteriology were the discoveries of the organisms causing
glanders (1862), relapsing fever (1868), typhoid fever (1880), tetanus (1885),
tuberculosis (1890), plague (1894), bacillary dysentery (1898), syphilis
(1905), and tularemia (1912).
Culture
A fundamental method of
studying bacteria is by culturing them in liquid media or on the surface of
media that have been solidified by agar. Media contain nutrients, varying from
simple sugars to complex substances such as meat broth. To purify or isolate a
single bacterial species from a mixture of different bacteria, solidified media
are generally used. Individual cells dividing on the surface of solidified
media do not move away from each other as they do in liquid, and after many
rounds of replication they form visible colonies composed of tens of millions
of cells all derived by binary fission from a single cell. If a portion of a
colony is then transferred to a liquid medium, it will grow as a pure culture,
free of all other bacteria except the single species that was found in the
colony.
Many different species of
bacteria so closely resemble one another in appearance that they cannot be
differentiated from one another under the microscope. Various culture
techniques have been developed to aid species identification. Some media
contain substances to inhibit the growth of many bacteria, but not the species
of interest. Others contain sugars that some but not all bacteria can use for
growth. Some media contain pH indicators that change color to indicate that a
constituent of the media has been fermented, yielding acid end products. Gas
production as an end product of fermentation can be detected by inoculating
bacteria in solidified media in tubes rather than on plates. Sufficient gas
production will result in the formation in the agar of bubbles that can easily
be seen. Still other media are formulated to identify bacteria that produce
certain enzymes that can break down constituents in the media; for example,
blood agar plates, which can detect whether bacteria produce an enzyme to lyse,
that is, dissolve red blood cells. The various culture media and culture
techniques are essential to the hospital laboratory, whose job it is to
identify the cause of various infectious diseases.
Sterilization
Drying or freezing kills
many species of bacteria and causes others to become inactive. Heat (or moist
heat above a certain temperature) kills all bacteria. Sterilization of many
different objects, such as spacecraft and surgical instruments, are important
facets of bacteriological work.
Microscopic Examination
The microscope is one of
the most important tools used in studying bacteria. Dyeing or staining bacterial
specimens or cultures was introduced in 1871 by the German pathologist Karl Weigert and has greatly helped the
bacteriologist in identifying and observing bacteria under the microscope. A
bacterial specimen is first placed on a glass slide. After the specimen has
dried, it is stained to render the organism easier to observe. Stains also
stimulate reactions in certain bacteria. For example, the tuberculosis bacillus
can be recognized only on the basis of its reaction to certain stains, such as
Gram's stain. Bacteriologists have been greatly aided by the electron
microscope, which has far stronger magnification powers than ordinary
microscopes.
Current Research
In recent years,
bacteriology has been greatly expanded from its concentration on disease-causing
pathogens. The discovery of nitrogen fixation by bacteria (in the root nodules
of leguminous plants) has led to attempts to inoculate the roots of other plant
strains and thereby increase soil fertility and the productivity of food crops.
Some bacteria are able to digest petroleum and other hydrocarbons; others
absorb phosphorus. These bacteria are being intensively investigated as
possible aids in cleaning up oil spills and removing phosphorus from sewage
sludge. Other bacteria may be more efficient than yeast at producing alcohol
and are being explored in the search for new energy sources. Escherichia
coli, a normal inhabitant of the human intestinal tract, is the most
thoroughly studied of all organisms. Studies of the mechanisms of genetic
exchange and the biology of plasmids and bacteriophages of E. coli have
been crucial in understanding many aspects of DNA replication and the
expression of genetic material. These studies have led to the ability to insert
DNA from unrelated organisms into E. coli plasmids and bacteriophages,
and to have that DNA replicated by the bacteria, with the genetic information
it contains expressed by the bacteria. It is thus possible for bacteria to
become living factories for scarce biological products such as human insulin,
interferon, and growth hormone. This process is called genetic engineering.
Louis pasteur 1822 –
1895
French chemist
and biologist, who founded the science of microbiology, proved the germ theory
of disease, invented the process of pasteurization, and developed vaccines for
several diseases, including rabies.
Pasteur was
born in Dôle on 7.12.1822, the son of a tanner, and grew up in the small town
of 
whereas when such a beam was passed
through a solution of artificially synthesized organic nutrients, no rotation
took place. If, however, bacteria or other micro-organisms were placed in the
latter solution, after a while it would also rotate light to the right or left.
Pasteur
concluded that organic molecules can exist in one of two forms, called isomers
(that is, having the same structure and differing only in being mirror images
of each other), which he referred to as “left-handed” and “right-handed” forms.
When chemists synthesize an organic compound, these forms are produced in equal
proportions, canceling each other's optical effects. Living systems, however,
which have a high degree of chemical specificity, can discriminate between the
two forms, metabolizing one and leaving the other untouched and free to rotate
light.
Work on Fermentation
After spending several
years of research and teaching at 
production of alcohol in fermentation is indeed due to
yeast and that the undesired production of substances (such as lactic acid or
acetic acid) that make wine sour is due to the presence of additional
organisms, such as bacteria. The souring of wine and beer had been a major
economic problem in
Pasteur extended these
studies to such other problems as the souring of milk, and he proposed a
similar solution: heating the milk to a high temperature and pressure before
bottling. This process is now called pasteurization.
Disproof of Spontaneous
Generation
Fully aware of
the presence of micro-organisms in nature, Pasteur undertook several
experiments designed to address the question of where these “germs” came from.
Were they spontaneously produced in substances themselves, or were they
introduced into substances from the environment? Pasteur concluded that the
latter was always the case. His findings resulted in a fierce debate with the
French biologist Félix Pouchet—and later with the noted English bacteriologist
Henry Bastion—who maintained that under appropriate conditions instances of spontaneous generation could be found. These debates,
which lasted well into the 1870’s, although a commission of the Academy of
Sciences officially accepted Pasteur's results in 1864, gave great impetus to
improving experimental techniques in microbiology.
Silkworm Studies
In 1865 Pasteur was
summoned from
Germ Theory of Disease
Pasteur's work
on fermentation and spontaneous generation had considerable implications for medicine, because he
believed that the origin and development of disease are analogous to the origin
and process of fermentation. That is, disease arises from germs attacking the
body from outside, just as unwanted micro-organisms invade milk and cause
fermentation. This concept, called the germ theory of disease, was strongly
debated by doctors and scientists around the world. One of the main arguments
against it was the contention that the role germs played during the course of
disease was secondary and 
unimportant; the notion that tiny
organisms could kill vastly larger ones seemed ridiculous to many people.
Pasteur's studies convinced him that he was right, however, and in the course
of his career he extended the germ theory to explain the causes of many
diseases.
Anthrax Research
Pasteur also
determined the natural history of anthrax, a fatal disease of cattle. He proved that anthrax is
caused by a particular bacillus and suggested that animals could be given
anthrax in a mild form by vaccinating them with attenuated (weakened) bacilli,
thus providing immunity from potentially fatal attacks. In order to prove his
theory, Pasteur began by inoculating 25 sheep; a few days later he inoculated
these and 25 more sheep with an especially strong inoculant, and he left 10
sheep untreated. He predicted that the second 25 sheep would all perish and
concluded the experiment dramatically by showing, to a skeptical crowd, the
carcasses of the 25 sheep lying side by side.
Rabies Vaccine
Pasteur spent the rest of
his life working on the causes of various diseases—including septicemia,
cholera, diphtheria, fowl cholera, tuberculosis, and smallpox—and their
prevention by means of vaccination. He is best known
for his investigations concerning the prevention of rabies, otherwise known in humans as hydrophobia. After
experimenting with the saliva of animals suffering from this disease, Pasteur
concluded that the disease rests in the nerve centers of the body; when an
extract from the spinal column of a rabid dog was injected into the bodies of
healthy animals, symptoms of rabies were produced. By studying the tissues of
infected animals, particularly rabbits, Pasteur was able to develop an
attenuated form of the virus that could be used for inoculation.
In 1885 a young
boy and his mother arrived at Pasteur's laboratory; the boy had been bitten
badly by a rabid dog, and Pasteur was urged to treat him with his new method.
At the end of the treatment, which lasted ten days, the boy was being
inoculated with the most potent rabies virus known; he recovered and remained
healthy. Since that time, thousands of people have been saved from rabies by
this treatment.
Pasteur's
research on rabies resulted, in 1888, in the founding of a special institute in
Hideyo
Noguchi 1876 – 1928
Japanese bacteriologist, who was the first to
obtain pure cultures of Trepanema pallidum, the spirochete that causes
syphilis, and to demonstrate the syphilitic origin of certain forms of general
paralysis. Born in
