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Chapter 1

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The Early Years of Microbiology

• What Does Life Really Look Like?

• Antoni van Leeuwenhoek

• Began making and using simple microscopes

• Often made a new microscope for each specimen

• Examined water and visualized tiny animals, fungi, algae,

and single-celled protozoa: "animalcules"

• By end of 19th century, these organisms were called

microorganisms; now they are also called microbes

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Figure 1.1 Antoni van Leeuwenhoek.

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Lens Specimen holderFigure 1.2 Reproduction of Leeuwenhoek's microscope.

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Figure 1.3 The microbial world.

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Carolus Linnaeus developed taxonomic system for

naming plants and animals and grouping similar organisms together

• Leeuwenhoek's microorganisms are now grouped into six categories: • Bacteria• Archaea• Fungi• Protozoa• Algae• Small multicellular animals

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Bacteria and Archaea

• Prokaryotic (lack nuclei)

• Much smaller than eukaryotes

• Found everywhere there is sufficient moisture; some have been isolated from extreme environments

• Reproduce asexually

• Bacterial cell walls contain peptidoglycan; some lack cell walls

• Archaeal cell walls are composed of polymers other than peptidoglycan

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Prokaryoticbacterial cells

Nucleus ofeukaryotic cheek cell

Figure 1.4 Cells of the bacterium Streptococcus (dark blue) and two human cheek cells.

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Fungi

• Eukaryotic (have membrane-bound nucleus)

• Obtain food from other organisms

• Possess cell walls

• Include

• Molds – multicellular; grow as long filaments;

reproduce by sexual and asexual spores

• Yeasts – unicellular; reproduce asexually by budding;

some produce sexual spores

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SporesHyphae Budding cellsFigure 1.5 Fungi.

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Protozoa

• Single-celled eukaryotes• Similar to animals in nutrient needs and cellular structure• Live freely in water; some live in animal hosts• Asexual (most) and sexual reproduction• Most are capable of locomotion by

• Pseudopods – cell extensions that flow in direction of travel

• Cilia – numerous short protrusions that propel organisms through environment

• Flagella – extensions of a cell that are fewer, longer, and more whiplike than cilia

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PseudopodsNucleus Cilia

Flagellum

Figure 1.6 Locomotive structures of protozoa.

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Algae

• Unicellular or multicellular

• Photosynthetic

• Simple reproductive structures

• Categorized on the basis of pigmentation and composition

of cell wall

• Scientists and manufacturers use many algae-derived

products

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Figure 1.7 Algae.

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The Early Years of Microbiology

• How Can Microbes Be Classified?• Other Organisms of Importance to Microbiologists

• Parasites

• Viruses

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Red blood cellFigure 1.8 An immature stage of a parasitic worm in blood.

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Virus

Bacterium

Virusesassemblinginside cell

Figure 1.9 A colorized electron microscope image of viruses infecting a bacterium.

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The Early Years of Microbiology

• Tell Me Why• Other Organisms of Importance to Microbiologists

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The Golden Age of Microbiology

• Scientists searched for answers to four questions

• Is spontaneous generation of microbial life possible?

• What causes fermentation?

• What causes disease?

• How can we prevent infection and disease?

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• Some philosophers and scientists of the past thought

living things arose from three processes:

• Asexual reproduction

• Sexual reproduction

• Nonliving matter

• Aristotle proposed spontaneous generation

• Living things can arise from nonliving matter

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• Redi's experiments

• When decaying meat was kept isolated from flies,

maggots never developed

• Meat exposed to flies was soon infested

• As a result, scientists began to doubt Aristotle's theory

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Figure 1.10 Redi's experiments.

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• Needham's experiments

• Scientists did not believe that animals could arise

spontaneously, but that microbes could

• Needham's experiments with beef gravy and infusions of

plant material reinforced this idea

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• Spallanzani's experiments

• Results contradicted Needham's findings• Concluded that

• Needham failed to heat vials sufficiently to kill all microbes or had not sealed vials tightly enough

• Microorganisms exist in air and can contaminate experiments

• Spontaneous generation of microorganisms does not occur

• The debate continued until the experiments conducted by Louis Pasteur

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Figure 1.11 Louis Pasteur.

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• Pasteur's experiments

• Performed investigations of spontaneous generation

• When the "swan-necked" flasks remained upright, no

microbial growth appeared

• When the flask was tilted, dust from the bend in the neck

seeped back into the flask and made the infusion cloudy

with microbes within a day

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Figure 1.12 Pasteur's experiments with "swan-necked flasks."

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The Golden Age of Microbiology

• Does Microbial Life Spontaneously Generate?• The scientific method

• Debate over spontaneous generation led in part to

development of scientific method

• Observation leads to question

• Question generates hypothesis

• Hypothesis is tested through experiment(s)

• Results prove or disprove hypothesis

• Accepted hypothesis can lead to theory/law

• Disproved hypothesis is rejected or modified

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Figure 1.13 The scientific method, which forms a framework for scientific research.

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The Golden Age of Microbiology

• What Causes Fermentation?• Spoiled wine threatened livelihood of vintners

• Some believed air caused fermentation; others insisted

living organisms caused fermentation

• Vintners funded research of methods to promote

production of alcohol and prevent spoilage during

fermentation

• This debate also linked to debate over spontaneous

generation

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Figure 1.14 How Pasteur applied the scientific method in investigating the nature of fermentation.

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The Golden Age of Microbiology

• What Causes Fermentation?• Pasteur's experiments

• Led to the development of pasteurization

• Process of heating liquids just enough to kill most

bacteria

• Began the field of industrial microbiology

• Intentional use of microbes for manufacturing products

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The Golden Age of Microbiology

• What Causes Fermentation?• Buchner's experiments

• Demonstrated fermentation does not require living cells

• Showed enzymes promote chemical reactions

• Began the field of biochemistry

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The Golden Age of Microbiology

• What Causes Disease?• Pasteur developed germ theory of disease

• Robert Koch studied disease causation (etiology)

• Anthrax

• Examined colonies of microorganisms

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Figure 1.15 Robert Koch.

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The Golden Age of Microbiology

• What Causes Disease?• Koch's experiments

• Simple staining techniques

• First photomicrograph of bacteria

• First photomicrograph of bacteria in diseased tissue

• Techniques for estimating CFU/ml

• Use of steam to sterilize media

• Use of Petri dishes

• Techniques to transfer bacteria

• Bacteria as distinct species

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Bacterium 1

Bacterium 2

Bacterium 3

Bacterium 4

Bacterium 5Bacterium 6 Bacterium 7

Bacterium 8

Bacterium 9

Bacterium 10

Bacterium 11

Bacterium 12

Figure 1.16 Bacterial colonies on a solid surface (agar).

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The Golden Age of Microbiology

• What Causes Disease?• Koch's postulates

• Suspected causative agent must be found in every case

of the disease and be absent from healthy hosts

• Agent must be isolated and grown outside the host

• When agent is introduced into a healthy, susceptible host,

the host must get the disease

• Same agent must be found in the diseased experimental

host

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Gram-positive Gram-negativeFigure 1.17 Results of Gram staining.

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The Golden Age of Microbiology

• How Can We Prevent Infection and Disease?• Many great advances in disease prevention came after

it was shown that microbes can cause disease

• Modern principles of hygiene not widely practiced in the

mid-1800s

• Healthcare associated infections were common

• Six health care practitioners were instrumental in

changing health care delivery methods

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The Golden Age of Microbiology

• How Can We Prevent Infection and Disease?• Semmelweis and handwashing

• Ignaz Semmelweis required medical students to wash

their hands in chlorinated lime water

• Resulted in higher patient survival rates

• Lister's antiseptic technique

• Joseph Lister advanced antisepsis in health care settings

• Sprayed wounds, surgical incisions, and dressings with

carbolic acid (phenol)

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The Golden Age of Microbiology

• How Can We Prevent Infection and Disease?• Nightingale and nursing

• Florence Nightingale introduced cleanliness and

antiseptic techniques into nursing practice

• Advocated for hospital and public health policy reform

• Snow and epidemiology

• John Snow mapped cholera epidemic in London in 1854

• His work was the foundation for infection control and

epidemiology

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Figure 1.18 Florence Nightingale.

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The Golden Age of Microbiology

• How Can We Prevent Infection and Disease?• Jenner's vaccine

• Edward Jenner developed a vaccine against smallpox

• Demonstrated the validity of vaccination

• Began the field of immunology

• Ehrlich's "magic bullets"

• Paul Ehrlich worked to identify "magic bullets" that would

destroy pathogens but not harm humans

• Discoveries began the field of chemotherapy

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Figure 1.19 Some of the many scientific disciplines and applications that arose from the pioneering work of scientists just before and around the time of the Golden Age of Microbiology.

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The Golden Age of Microbiology

• Tell Me Why• Some people consider Pasteur or Koch to be the Father

of Microbiology, rather than Leeuwenhoek. Why might

they be correct?

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The Modern Age of Microbiology

• What Are the Basic Chemical Reactions of Life?• Biochemistry

• Study of metabolism: the chemical reactions that occur in

living organisms

• Began with Pasteur's work on fermentation and Buchner's

discovery of enzymes in yeast extract

• Kluyver and van Niel proposed basic biochemical reactions

shared by all living things

• Microbes used as model systems for biochemical reactions

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The Modern Age of Microbiology

• What Are the Basic Chemical Reactions of Life? • Biochemistry

• Practical applications

• Design of herbicides and pesticides

• Diagnosis of illnesses and monitoring of patients'

responses to treatment

• Treatment of metabolic diseases

• Drug design

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The Modern Age of Microbiology

• How Do Genes Work?• Genetics: scientific study of inheritance

• Many advances in the discipline made through the study

of microbes

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The Modern Age of Microbiology

• How Do Genes Work?• Microbial genetics

• Avery, MacLeod, and McCarty determined that genes are

contained in molecules of DNA

• Beadle and Tatum established that a gene's activity is

related to protein function

• Explained translation of genetic information into protein

• Investigated rates and mechanisms of genetic mutation

• Determined how cells control genetic expression

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The Modern Age of Microbiology

• How Do Genes Work?• Molecular biology

• Explanation of cell function at the molecular level• Pauling proposed that gene sequences could

• Provide understanding of evolutionary relationships and processes

• Establish taxonomic categories to reflect these relationships

• Identify existence of microbes that have never been cultured

• Woese determined that cells belong to domains Bacteria, Archaea, or Eukarya

• Cat scratch disease caused by unculturable organism

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The Modern Age of Microbiology

• How Do Genes Work?• Recombinant DNA technology

• Genes in microbes, plants, and animals manipulated for

practical applications

• Production of human blood-clotting factor by E. coli to aid

hemophiliacs

• Gene therapy

• Inserting a missing gene or repairing a defective one in

humans by inserting desired gene into host cells

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The Modern Age of Microbiology

• What Role Do Microorganisms Play in the

Environment?• Bioremediation uses living bacteria, fungi, and algae to

detoxify polluted environments

• Recycling of chemicals such as carbon, nitrogen, and

sulfur

• Most microbes in the environment are not pathogenic

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The Modern Age of Microbiology

• How Do We Defend Against Disease?• Serology

• The study of blood serum

• Von Behring and Kitasato – presence in the blood of chemicals and cells that fight infection

• Immunology• The study of the body's defenses against specific

pathogens

• Chemotherapy• Fleming discovered penicillin

• Domagk discovered sulfa drugs

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Fungus colony(Penicillium)

Zone of inhibition

Bacteria(Staphylococcus)

Figure 1.20 The effects of penicillin on a bacterial "lawn" in a Petri dish.

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The Modern Age of Microbiology

• What Will the Future Hold?• Microbiology is built on asking and answering questions

• The more questions we answer, the more questions we

have

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The Modern Age of Microbiology

• Tell Me Why• Why are so many modern questions in microbiology

related to genetics?

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Important topics

Antoni van Leeuwenhoek’s and Semmelweis findings The general characteristics of bacteria, archaea, virus,

protozoa, fungus, algae To differentiate the prokaryotes and eukaryotes Enzyme, a protein that runs the chemical reactions in the

cell.