The science of microbiology can be divided into theoretical and applied fields. Farmers are applied scientists. They use microbiological principles to get the best yields from their farms. Doctors are applied microbiologists too, because their primary interest is to keep people healthy through the use of scientific knowledge.
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The theoretical scientist does not have in mind any specific use for the new knowledge gained. The purpose is to obtain new information to see how it fits the “old laws,” and write “new laws” if necessary.
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While investigating the cause of wine spoilage in the vineyards of France, Louis Pasteur became interested in the theoretical problem of whether life could be generated from nonliving material. Much of his theoretical work led to very practical applications.
His theory that there were very small organisms causing diseases and decay led to the development of vaccinations and the preservation of food by pasteurization.
At this point, however, it is important to note that the study of microbiology is much like the study of a foreign language. The vocabulary includes a great many new words. Once you learn the meaning of these words and how to use them properly, the science of microbiology will be much easier.
Many terms refer to the organism being studied; others refer to the activities of a particular organism and using them improperly could lead to a misunderstanding. For example, the words John Smith tell you who a person is, while the word microbiologists tell you what a person does.
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A brief look at each of the applied fields of microbiology may give some understanding of how microbes influence our lives.
Medical microbiology is probably a very familiar field since it deals with microbes which cause diseases in humans, animals, and many plants. When asked of their knowledge of microbiology, people will mention something about a sickness or disease that they have had themselves.
The “flu’ (influenza), strep throat, tetanus, and malaria are all examples of diseases that are caused by the activities of microbes. In medical microbiology, the microbes that cause illness are called pathogens. The term disease means a process or event those results in illness or harm to a living organism.
The infectious disease refers to the fact that some microbes are able to go, through the process of entering another organism, growing, arid causing harm. Some of these microbes may cause only minor damage, while infection by others may result in quick death.
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Some microbes can spread through a population and cause disease. Over one hundred years of work was needed to show that a particular illness was caused by the actions of particular microbes that were able to be transmitted from one individual to another.
The bacteria that cause the disease cholera (Vibrio cholerae) were not identified with the symptoms they produced until 1883. Today our understanding that microbes can spread through a population and cause a particular disease is known as the germ theory of disease.
Using this theory as a pattern for research has led to a greater understanding of the disease process. The germ theory of disease has become a unifying concept in that it defines the role of microbes in the disease process.
Before the germ theory, many diseases were suspected to have causes ranging from those caused by “evil spirits” to unknown “miasmas” emanating from the soil or earth. Today we know a particular microbe may cause a number of different illnesses.
An infection by one microbe may show different symptoms or signs depending on where it becomes located in the body. When a bacterium is located in the lung it may cause pneumonia, while in the joints it may cause arthritis, or meningitis in the spinal cord or brain.
Medical microbiology also deals with disease prevention, the body’s resistance to disease-causing organisms, and ways in which sick persons may be helped to recover.
Foods must be transported great distance and stored for long period for the world to have a safe, nutrition’s food supply. To accomplish this, the role of microbes in food poisoning, spoilage, and preservation must be investigated. Contributions to the field of food and dairy microbiology have helped resolve many food problems.
When microbes enter a food they may either cause it to spoil, make it dangerous to eat, or change it to another form that it still acceptable as a food. Scientists have had to find out how the microbe enters the food, what action it has, and how to control the microbe.
The whole idea of preserving foods is based on preventing microbial growth. Pasteurization is one of the best-known methods used to prevent spoilage and the transfer to disease. This heating procedure was first used in the wine industry in an attempt to keep wine from being changed into vinegar.
This worked so well that other food industries now use the process Cheeses, beer, and milk are usually pasteurized to reduce the number of harmful microbes in the food.
In some cases, microbes are intentionally mixed with foods to change the food to another form. When certain bacteria are added to milk and encouraged to grow under controlled conditions, the milk is converted to cheese.
The food value of cheese is very high, and it is much easier to store than milk. The many different kinds of cheeses found in the world are also the result of the actions of different microbes. The favour, smell, and texture of a cheese are determined by the kinds of microbes that are grown in the milk.
Water in our environment commonly contains microbes. The kinds of microbes and their method of entering the water is of great concern since many waterborne microbes can cause human disease.
The field of water and wastewater microbiology explores all of these areas. The ultimate source of water is from rain or precipitation.
The water moves over the surface of the ground as rivers and streams or through the earth as groundwater. Microbes and chemicals may enter the water from the air as the water passes through it or from untreated or poorly treated sewage being dumped into a body of water.
Drinking water and industrial water are pumped from lakes, rivers, and wells. This water must be cleared of harmful bacteria, viruses, and other microbes to control diseases and prevent fouling of industrial equipment. Cholera and typhoid fever are diseases that are able to be transferred in water. Purification plants throughout the country treat water before it is used.
Wastewater treatment plants treat water before it is again released into the environment. In some cases, water becomes clouded with large amounts of chemicals, mud, and plant material. Unless this water is fast moving and well aerated, microbes will use these materials for food and produce poisons or foul odors.
Soil contains great numbers of many microbe types. Bacteria, algae, and fungi are commonly found in rich, fertile soils. The more fertile the soil, the more likely it is to contain a thriving population of microbes.
An effort to maintain good farm production has led microbiologists to develop the field of soil and agricultural microbiology. Microbes are responsible for the decomposition and decay of dead plants and animals.
If it were not for microbial decomposition, the earth would be covered with all types of decaying organisms. The molecules in these would stay locked-up and unavailable for reuse by other, younger organisms.
The recycling of materials through decay activities in the soil is vital to all life. Sewage treatment plants are, in part, giant microbial cultures for speeding decay of waste products. The waste material put into compost piles is broken down as a result of microbial activity and becomes rich, soil-fertilizing material for plants.
The increased amount of solid waste throughout the world along with the increase in human population has made it essential to explore new ways of controlling decay. Agricultural microbiology deals with those microbes associated with animals.
For examples, cattle and other animals with rumens, or “second stomachs,” and laiden with microbes. These are of great value to the health of the animal. The food they eat, silage, is grain that has been preserved by the action of microbes while the grain has been stored in a silo.
Due to the small size of microbes, simple test tubes and covered dishes can provide enough space to grow them for tests and explore their activities.
However, many microorganisms are capable of producing products of value to humans, if they can be produced in very large quantities. Microbiologists, engineers, and business have come together for this purpose and developed the field of industrial microbiology.
This area involves the large-scale growth of particular microbes. Yeast, bacteria, and molds may be grown in 5, 10, or even 50,000 gallon containers. For example, yeast cells are grown for use in ironized yeast tablets for human use and in even larger quantities as a supplement to farm animal feed.
In other instances, the by-product of the growth and activities of a microbe is the most useful. These include enzymes, amino acids, antibiotics, alcohol, and organic acids. Handling large quantities of growing microbes is not easy. Expensive equipment and well-trained personnel are essential to the smooth production.
Industrial microbiologists must closely monitor the microbes’ chemical activities and be prepared to change or stop the activities of the organism to prevent product loss. Careful attention must also be paid to ensure that only one kind of microbe is being grown. Successful control of these factors has resulted in the development of multimillion dollar microbial industries.
A vast amount of chemical and microbiological information has been gained from studies in the various microbiology fields. These efforts have resulted in solutions to many problems, and have also revealed new and more challenging areas of concern.
A better understanding of the scope of microbiology may be gained by taking a brief look at the history of microbiology and some of the questions explored by famous microbiologists.
For centuries, one of the most intriguing questions related to the origin of life. Even though the answer still continues to be an area of speculation, research and experimental attempts to explain the origin of life have inadvertently been prime movers in expanding our knowledge of microbiology. In simpler times, the origin of life from nonliving things was never doubted.
The Greeks, Romans, Chinese, and many other ancients believed that maggots, lice, frogs, and even mice could spontaneously arise from mud. They thought they saw these events happening every day it was thought that mice could be produced from a sweaty shirt if it was kept in a dark, cool room with several grains of wheat.
Many prominent scientists believed in this concept. Only through the efforts of scientific investigators like Redi, Spallanzani, and Pasteur was this classical concept of spontaneous generation (abiogenesis) discarded.
The argument between the supporters of spontaneous generation and those of biogenesis has lasted over 300 years. People believing in biogenesis thought that all living things came from pre-existing life. During this period, the cleverness and imagination of those involved were used to the fullest in the attempt to disprove the others’ position.
Even though microbes could not be seen, a number of people suspected that such small living things existed. In the first century B.C. Varro suggested that diseases were due to invisible organisms. Later in 1546, Fracastorius wrote the books, De Contagione.
The contained the first scientific statements as to how infections were transmitted. Fracastorius was medical adviser to the Council of Trent (Italy), which had to be transferred to Bologna because of an outbreak of typhus fever.
He wrote, “Contagion is precisely similar putrefaction which passes from one thing to another: its germs (seminaria) have great activity, they are made up of a strong and viscous combination, and they have not only a material but also a spiritual antipathy to the animal organism.” Fracastorius believed even at this early date that consumption (tuberculosis) was able to transfer from person to person.
He commented, “It is extraordinary to see in families up to the fifth and sixth generation all the members die of phthisis (tuberculosis) at the same age.”
But it was Francesco Redi (1668) who set up the first controlled experiment to disprove those who supported spontaneous generation. This is the best type of experimental setup from which to draw conclusions, since there is only one unknown factor in question. Redi used two sets of dishes and varied only one part of the experiment These experiments ended the concept of spontaneous generation for only a short period of time.
In 1676, the idea of spontaneous generation was accidentally revived, due to the tinkering of a Dutch clothier, Anton van Leeuwenhoek. His discovery of “animalcules,” little animals, while using lenses reopened the debate. Leeuwenhoek’s successful method of grinding lenses allowed him to construct over 200 microscopes (all disposable), capable of magnifying a specimen to 300 times its normal size.
The images were to clear that Leeuwenhoek made drawings of what we now know to be bacteria. These were submitted to the influential Royal Society of London and were so impressive that many others began exploring the world of microbes and attempting to resolve the questions of spontaneous generation.
Where did these new life forms come from? Another scientist, Lazaro Spallanzani (1729-99) benefited from Redi’s use of controlled experiments and successfully put to rest the spontaneous generation theory once more.
In response to a challenge by Joseph Needham, an English priest and naturalist, Spallanzani devised an experiment that not only settled the argument, but demonstrated that heating a container and using an airtight seal would prevent spoilage of foods. No “animalcules” were generated in his experiment.
This experiment on the origin of life ultimately led to the basic preservative methods used in the commercial canning industry.
Spallanzani’s evidence supported the theory of biogenesis until 1775 when Lovosier and Priestly discovered oxygen. This discovery brought on another wave of interest in spontaneous generation.
It was suggested that since oxygen was excluded from Spallanzani’s experiment, the spontaneous generation of life was prevented. With this new challenge to the theory of biogenesis, Louis Pasteur (1869) began to experiment with the origin of bacteria and their need for oxygen.
He successfully defended the biogenic theory. Even though Pasteur’s original work was designed to investigate biogenesis, he gathered much other information related to microbes and their activities.