Chapter 1
Microbiology: Then and Now
1.1
The Beginnings of Microbiology
 Microscopy—Discovery of the Very Small
• Robert Hooke published Micrographia in 1665
• Anton von Leeuwenhoek was skilled in grinding lenses and described
“animalcules” in a specimen of lake water
 Experimentation—Can Life Generate Itself Spontaneously?
• In the 1600s, many people thought life generated spontaneously from
putrid and decaying materials
• Leeuwenhoek suggested maggots arose from eggs in the decaying
material, not the material itself
• Francesco Redi found that if flies were prevented from landing on meat, it
did not produce maggots
• In 1859, Louis Pasteur discredited the idea of spontaneous generation
1.2
Microorganisms and Disease Transmission
 Epidemiology—Understanding Disease Transmission
• Epidemiology is the study of the source, cause, and mode of transmission
of disease
• Ignaz Semmelweis determined the source of blood poisoning of women in
childbirth
• John Snow determined the cause of cholera transmission in London
 Variolation and Vaccination—Prevention of Infectious Diseas
• Variolation involved exposing individuals to dried smallpox specimens
• Edward Jenner developed vaccination, inoculating individuals with
cowpox
 The Stage is Set
• Advances in microscopy allowed for more investigation of microbes
• In 1840, Jacob Henle implicated bacteria in disease causation
1.3
The Classical Golden Age of Microbiology (1854—1914)
 Louis Pasteur Proposes that Germs Cause Infectious Disease
• Louis Pasteur proved that yeasts were responsible for fermentation
• Pasteurization was his technique of heating to kill pathogens
• He proposed the germ theory in 1862
• Pasteur’s Work Stimulates Disease Control and Reinforces Disease Causation
• Joseph Lister developed the practice of antisepsis, chemical disinfection of
external living surfaces
• Pasteur also investigated the cause of cholera and the silkworm disease
(pébrine)
 Robert Koch Formalizes Standards to Identify Germs with Infectious Diseases
• Koch’s postulates became standards for linking a specific organism to a
specific disease
 Koch Develops Pure Culture Techniques
• By adding gelatin to his broth, Koch was able to grow bacterial colonies in
a Petri dish
 Competition Fuels the Study of Infectious Disease
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1.5
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Pasteur experimented with attenuated bacterial cells for use in cholera and
anthrax inoculations
• Émile Roux and Alexandre Yersin linked diphtheria toxin to bacterial cells
• Emil von Behring treated diphtheria with an antitoxin
• Elie Metchnikoff described phagocytosis
Competition Fuels the Study of Infectious Disease (cont.)
• Pasteur developed a successful rabies vaccine
• Koch isolated the tubercle bacillus and determined that water is the key to
tuberculosis transmission
• Pasteur, Koch, and their colleagues put bacteriology on the map
Other Global Pioneers Contribute to New Disciplines in Microbiology
• Early observations of viruses were made by Dimitri Ivanowsky, Martinus
Beijerinck, and Walter Reed.
• Sergei Winogradsky developed the concept of nitrogen fixation by
bacteria
Studying Microorganisms
Why Study Microorganisms and Viruses Today?
• There is still much to learn and understand
• It is an opportunity to study processes common to all life
• Microorganisms are not only important in disease but also in
environmental processes
The Spectrum of Microorganisms Is Diverse
• There are over 10 million species of prokaryotes that appear in spherical,
spiral, or rod-shaped forms
• There are two domains of prokaryotes, Bacteria and Archaea
The Spectrum of Microorganisms Is Diverse (cont.)
• There are over 3600 known viruses
• Viruses are not actually microbes and are not cells–they have a DNA or
RNA core surrounded by a protein coat
• Viruses cannot replicate without the replication machinery in a host cell
The Spectrum of Microorganisms Is Diverse (cont.)
• There are about 70,000 described species of fungi
• Most fungi live in their food medium and may cause human disease;
others are useful antibiotics
The Spectrum of Microorganisms Is Diverse (cont.)
• Single-celled protozoa and algae are protista, some of which are freeliving and some of which live symbiotically with other organisms
• Some protozoa can cause disease in humans
The Second Golden Age of Microbiology (1943—1970)
Molecular Biology Relies on Microorganisms
• Salvador Luria and Max Dulbrück discovered that bacteria can mutate to
generate resistance to viral infection
• George Beadle and Edward Tatum demonstrated that one gene codes for
one enzyme
• Early work on DNA as the genetic material was done by Oswald Avery,
Colin MacLeod, Maclyn McCarty, Alfred Hershey, and Martha Chase
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Two Types of Cellular Organization Are Realized
• Eukaryotic (plant, animal, fungi, protist) cells contain a membrane-bound
nucleus
• Prokaryotic (bacteria, archaea) cells lack a membrane-bound nucleus
Antibiotics Are Used to Cure Infectious Disease
• In 1910, Paul Erlich developed Salvarsan, a chemical that cured
individuals of syphilis
• In 1929, Alexander Fleming observed that a species of Penicillium mold
killed bacterial cells, leading to the development of penicillin
• Bacterial species can become resistant to antibiotics
The Third Golden Age of Microbiology—Now
Microbiology Continues to Face Many Challenges
• Infectious diseases kill about 15 million people each year
• A pathogen can cause more than one disease, and a disease can be caused
by more than one microbe (polymicrobial diseases)
• Pathogens are becoming resistant to antimicrobials
• New diseases are emerging, and old diseases are reemerging
• Pathogens can be used intentionally to infect large numbers of people
through bioterrorism
Microbial Ecology and Evolution Are Helping to Drive the New Golden Age
• Molecular biology can help us study microbes that cannot be cultured in a
lab
• Phylogeny identifies evolutionary relationships between organisms
Microbes can exist in complex communities, called biofilms
Bioremediation is the use of microorganisms to remove or decontaminate toxic
materials in the environment