Burton's Microbiology for the Health Sciences 8th Edition_Paul_G._Englekirk_Gwendolyn
Microbiology: The Science
AFTER STUDYING THIS ... [Show More] CHAPTER, YOU SHOULD BE ABLE TO:
Define microbiology, pathogen, nonpathogen, and opportunistic pathogen
List several reasons why microorganisms are important (e.g., as a source of
Explain the relationship between microorganisms and infectious diseases
Differentiate between infectious diseases and microbial intoxications
Outline some of the contributions of Leeuwenhoek, Pasteur, and Koch to microbiology
Differentiate between biogenesis and abiogenesis
Explain the germ theory of disease
Outline Koch's postulates and cite some circumstances in which they may not apply
Discuss two medically related fields of microbiology
Welcome to the fascinating world of microbiology, where you will learn about creatures so small that
they cannot be seen w ith the naked eye. In this chapter, you will discover the effects that these
organisms have on our daily lives and the environment around us, and why knowledge of them is of
great importance to healthcare professionals. You will learn that some of these tiny creatures are our
friends, whereas others are our enem ies. You are about to embark on an exciting journey. En joy the
What Is Microbiology?
A microbiology course is an advanced biology course. Ideally, students taking microbiology should
have some background in biology. As you know, biology is the study of living organisms (from bios,
referring to living organisms, and logy, meaning “the study of”). Micro means very small—anything so
small that it must be viewed with a microscope (an optical instrument used to observe very small
objects). Therefore, microbiology is the study of very small living organisms—organisms called
microorganisms or microbes. Microorganisms are said to be ubiquitous, meaning they are virtually
The various categories of microorganisms include viruses, bacteria, archaeans, some algae, protozoa,
and some fungi (Fig. 1-1). These categories of microorganisms
are discussed in detail in Chapters 4 and 5. Because most scientists do not consider viruses to be
living organisms, they are often referred to as “infectious agents” or “infectious particles,” rather than
Your first introduction to microorganisms may have been when your mother warned you about
“germs” (Fig. 1-2). Although not a scientific term, “germs” are the microorganisms that cause disease.
Your mother worried that you might become infected with these types of microorganisms. Diseasecausing microorganisms are technically known as pathogens (Table 1-1). Actually, only about 3% of
known microbes are capable of causing disease (i.e., only about 3% are pathogenic). Thus, the vast
majority of known microorganisms are nonpathogens—microorganisms that do not cause disease.
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009Some of the nonpathogens are beneficial to us and some have no effect on us at all. In newspapers
and on television, we read and hear more about pathogens than we do about nonpathogens, but in this
book you will learn about both categories—the microorganisms that help us (“microbial allies”) and
those that harm us (“microbial enemies”).
Why Study Microbiology?
Although they are very small, microorganisms play significant roles in our lives. Listed below are a few
of the many reasons to take a microbiology course and to learn about microorganisms:
Figure 1-1. Family tree of microorganisms. Cellular microorganisms are divided into
eucaryotes (organisms having a true nucleus, such as algae, fungi, and protozoa) and
procaryotes (organisms lacking a true nucleus, such as archaeans and bacteria). Viruses
are not considered to be cells (they are said to be acellular) and are, therefore, not
included on this family tree. (The various categories of microorganisms are described in
Chapters 4 and 5.)
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 We have, living on and in our bodies (e.g., on our skin and in our mouths and intestinal tract),
approximately 10 times as many microorganisms as the total number of cells (i.e., epithelial
cells, nerve cells, muscle cells, etc.) that make up our bodies (10 trillion cells × 10 = 100 trillion
microbes). It has been estimated that perhaps as many as 500 to 1,000 different species of
microorganisms live on and in us. Collectively, these microbes are known as our indigenous
microflora (or indigenous microbiota) and, for the most part, they are beneficial to us. For
example, the indigenous microflora inhibit the growth of pathogens in those areas of the body
where they live by occupying space, depleting the food supply, and secreting materials (waste
products, toxins, antibiotics, etc.) that may prevent or reduce the growth of pathogens.
Indigenous microflora are discussed more fully in Chapter 10.
Figure 1-2. Germs. In all likelihood, your mother was your first microbiology
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 Some of the organisms that colonize (inhabit) our bodies are known as opportunistic
pathogens (or opportunists). Although such organisms do not usually cause us any problems,
they have the potential to cause infections if they gain access to a part of our anatomy where
they do not belong. For example, a bacterium called Escherichia coli (E. coli) lives in our
intestinal tracts. This organism does not cause us any harm as long as it stays in our intestinal
tract, but can cause disease if it gains access to our urinary bladder, bloodstream, or a wound.
Other opportunistic pathogens strike when a person becomes run down, stressed out, or
debilitated (weakened) as a result of some disease or condition. Opportunistic pathogens can be
thought of as microorganisms awaiting the opportunity to cause disease.
Microorganisms are essential for life on this planet as we
know it. For example, some microbes produce oxygen by the process known as photosynthesis
(discussed in Chapter 7). Actually, microorganisms contribute more oxygen to our atmosphere
than do plants. Thus, organisms that require oxygen—humans, for example—owe a debt of
gratitude to the algae and cyanobacteria (a group of photosynthetic bacteria) that produce
instructor. Not only did she alert you to the fact that there were “invisible” critters in
the world that could harm you, she also taught you the fundamentals of hygiene—
TABLE 1-1 Pathogens
CATEGORY EXAMPLES OF DISEASES THEY CAUSE
Algae A very rare cause of infections; intoxications (which result from
ingestion of toxins)
Bacteria Anthrax, botulism, cholera, diarrhea, diphtheria, ear and eye
infections, food poisoning, gas gangrene, gonorrhea, hemolytic
uremic syndrome (HUS), intoxications, Legionnaires' disease,
leprosy, Lyme disease, meningitis, plague, pneumonia, Rocky
Mountain spotted fever, scarlet fever, staph infections, strep throat,
syphilis, tetanus, tuberculosis, tularemia, typhoid fever, typhus,
urethritis, urinary tract infections, whooping cough
Fungi Allergies, cryptococcosis, histoplasmosis, intoxications, meningitis,
pneumonia, thrush, tinea (ringworm) infections, yeast vaginitis
Protozoa African sleeping sickness, amebic dysentery, babesiosis, Chagas'
disease, cryptosporidiosis, diarrhea, giardiasis, malaria,
meningoencephalitis, pneumonia, toxoplasmosis, trichomoniasis
Viruses Acquired immunodeficiency syndrome (AIDS), “bird flu,” certain
types of cancer, chickenpox, cold sores (fever blisters), common
cold, dengue, diarrhea, encephalitis, genital herpes infections,
German measles, hantavirus pulmonary syndrome (HPS),
hemorrhagic fevers, hepatitis, infectious mononucleosis, influenza,
measles, meningitis, mumps, pneumonia, polio, rabies, severe
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 Many microorganisms are involved in the decomposition of dead organisms and the waste
products of living organisms. Collectively, they are referred to as decomposers or saprophytes.
By definition, a saprophyte is an organism that lives on dead or decaying organic matter.
Imagine living in a world with no decomposers. Not a pleasant thought! Saprophytes aid in
fertilization by returning inorganic nutrients to the soil. They break down dead and dying organic
materials (plants and animals) into nitrates, phosphates, and other chemicals necessary for the
growth of plants (Fig. 1-3).
Some microorganisms are capable of decomposing industrial wastes (oil spills, for example).
Thus, we can use microorganisms—genetically engineered microbes, in some cases—to clean up
after ourselves. The use of microorganisms in this manner is called bioremediation, a topic
discussed in more detail in Chapter 10. Genetic engineering is discussed briefly in this section
and more fully in Chapter 7.
Many microorganisms are involved in elemental cycles (e.g., carbon, nitrogen, oxygen, sulfur,
and phosphorous cycles). In the nitrogen cycle, certain bacteria convert nitrogen gas in the air
to ammonia in the soil. Other soil bacteria then convert the ammonia to nitrites and nitrates. Still
other bacteria convert the nitrogen in nitrates to nitrogen gas, thus completing the cycle (Fig. 1-
4). Knowledge of these microbes is important to farmers who practice crop rotation to replenish
nutrients in their fields and to gardeners who keep compost pits as a source of natural fertilizer.
In both cases, dead organic material is broken down into inorganic nutrients (e.g., nitrates and
phosphates) by microorganisms. The study of the relationships between microbes and the
environment is called microbial ecology. Microbial ecology, the nitrogen cycle, and other
elemental cycles are discussed more fully in Chapter 10.
Algae and bacteria serve as food for tiny animals. Then, larger animals eat the smaller
creatures, and so on. Thus, microbes serve as important links in food chains (Fig. 1-5).
Microscopic organisms in the ocean, collectively referred to as plankton, serve as the starting
point of many food chains. Tiny marine plants and algae are called phytoplankton, whereas tiny
marine animals are called zooplankton.
Some microorganisms live in the intestinal tracts of animals, where they aid in the digestion of
food and, in some cases, produce substances that are of value to the
host animal. For example, the E. coli bacteria that live in the human intestinal tract produce
vitamins K and B
1, which are absorbed and used by the human body. Although termites eat
wood, they cannot digest wood. Fortunately for them, termites have cellulose-eating protozoa in
their intestinal tracts that break down the wood that the termites consume into smaller molecules
that the termites can use as nutrients.
acute respiratory syndrome (SARS), shingles, smallpox, warts,
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 Many microorganisms are essential in various food and beverage industries, whereas others are
used to produce certain enzymes and chemicals (Table 1-2). The use of microorganisms in
industry is called biotechnology, a topic discussed more fully in Chapter 10.
Figure 1-3. Saprophytes break down dead and decaying organic material into
inorganic nutrients in the soil.
Figure 1-4. Nitrogen fixation. Nitrogen-fixing bacteria that live on or near the roots of
legumes convert free nitrogen from the air into ammonia in the soil. Nitrifying
bacteria then convert the ammonia into nitrites and nitrates, which are nutrients used
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 Some bacteria and fungi produce antibiotics that are used to treat patients with infectious
diseases. By definition, an antibiotic is a substance produced by a microorganism that is
effective in killing or inhibiting the growth of other microorganisms. The use of microbes in the
antibiotic industry is another example of biotechnology. Production of antibiotics by
microorganisms is discussed in Chapters 9 and 10.
Microbes are essential in the field of genetic engineering.
In genetic engineering, a gene from one organism (e.g., from a bacterium, a human, an animal,
or a plant) is inserted into a bacterial or yeast cell. Because a gene contains the instructions for
the production of a gene product (usually a protein), the cell that receives the new gene can now
produce whatever product is coded for by that gene; so too can all of the cells that arise from
the original cell. Microbiologists have engineered bacteria and yeasts to produce a variety of
useful substances, such as insulin, various types of growth hormones, interferons, and materials
for use as vaccines. Genetic engineering is discussed more fully in Chapter 7.
For many years, microbes have been used as “cell models.” The more that scientists learned
about the structure and functions of microbial cells, the more they learned about cells in general.
The intestinal bacterium E. coli is one of the most studied of all microbes. By studying E. coli,
scientists have learned a great deal about the composition and inner workings of cells, including
Figure 1-5. Food chain. Tiny living organisms such as bacteria, algae, microscopic
aquatic plants (e.g., phytoplankton), and microscopic aquatic animals (e.g.,
zooplankton) are eaten by larger animals, which in turn are eaten by still larger
animals, etc., until an animal in the chain is consumed by a human. Humans are at
the top of the food chain.
TABLE 1-2 Products Requiring Microbial Participation in the Manufacturing
Foods Acidophilus milk, bread, butter, buttermilk, chocolate, coffee,
cottage cheese, cream cheese, fish sauces, green olives,
kimchi (from cabbage), meat products (e.g., country-cured
hams, sausage, salami), pickles, poi (fermented taro root),
sauerkraut, sour cream, sourdough bread, soy sauce, various
cheeses (e.g., cheddar, Swiss, Limburger, Camembert,
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009 Finally, we come to diseases. Microorganisms cause two categories of diseases: infectious
diseases and microbial intoxications (Fig. 1-6). An infectious disease results when a pathogen
colonizes the body and subsequently causes disease. A microbial intoxication results when a
person ingests a toxin (poisonous substance) that has been produced by a microorganism. Of
the two categories, infectious diseases cause far more illnesses and deaths. Infectious diseases
are the leading cause of death in the world and the third leading cause of death in the United
States (after heart disease and cancer). Worldwide, infectious diseases cause about 50,000
deaths per day; the majority of deaths occur in developing countries. Anyone pursuing a career
in a healthcare profession must be aware of infectious diseases, the pathogens that cause them,
the sources of the pathogens, how these diseases
are transmitted, and how to protect yourself and your patients from these diseases. Physicians'
assistants, nurses, dental assistants, laboratory technologists, respiratory therapists, orderlies,
nurses' aides, and all others who are associated with patients and patient care must take
precautions to prevent the spread of pathogens. Harmful microorganisms may be transferred
from health workers to patients; from patient to patient; from contaminated mechanical devices,
instruments, and syringes to patients; from contaminated bedding, clothes, dishes, and food to
patients; and from patients to healthcare workers, hospital visitors, and other susceptible
persons. To limit the spread of pathogens, sterile, aseptic, and antiseptic techniques (discussed
in Chapter 12) are used everywhere in hospitals, nursing homes, operating rooms, and
laboratories. In addition, the bioterrorist activities of recent years serve to remind us that
everyone should have an understanding of the agents (pathogens) that are involved and how to
protect ourselves from becoming infected. Bioterrorist and biological warfare agents are
discussed in Chapter 11. Additional information about microbial intoxications can be found in
CD-ROM Appendix 1 (“Microbial Intoxications”).
Roquefort and other blue cheeses), vinegar, yogurt
Ale, beer, brandy, sake (rice wine), rum, sherry, vodka, whiskey,
Chemicals Acetic acid, acetone, butanol, citric acid, ethanol, formic acid,
glycerol, isopropanol, lactic acid
Antibiotics Amphotericin B, bacitracin, cephalosporins, chloramphenicol,
cycloheximide, cycloserine, erythromycin, griseofulvin,
kanamycin, lincomycin, neomycin, novobiocin, nystatin,
penicillin, polymyxin B, streptomycin, tetracycline
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http://thepointeedition.lww.com/pt/re/9780781771955/bookContentPane_frame.htm;jsessi... 10/5/2009First Microorganisms on Earth
Perhaps you have wondered how long microorganisms have existed on earth. Scientists tell us that the
earth was formed about 4.5 billion years ago and, for the first 800 million to 1 billion years of earth's
existence, there was no life on this planet. Fossils of primitive microorganisms (as many as 11
different types) found in ancient rock formations in northwestern Australia date back to about 3.5
billion years ago. By comparison, animals and humans are relative newcomers. Animals made their
appearance on Earth between 900 and 650 million years ago (there is some disagreement in the
scientific community about the exact date), and, in their present form, humans (Homo sapiens) have
existed for only the past 100,000 years or so. Candidates for the first microorganisms on earth are
archaeans and cyanobacteria; these microorganisms are discussed in Chapter 4. [Show Less]