Microbiology: Then and Now

Chapter 1

1.1The 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

1.2Microorganisms 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

1.3The 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

•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

1.4Studying 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 free-living and some of which live symbiotically with other organisms

•Some protozoa can cause disease in humans

1.5The 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

•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

1.6The 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