Chapter 1: A Brief History of
Microbiology
Microbiology:
The study of microorganisms.
Microorganisms: Small living organisms that
generally can not be seen with the naked eye.
Include:
Bacteria
Fungi (yeasts and molds)
Protozoa
Algae
Multicellular parasites
Also include nonliving infectious agents:
Viruses
 Prions
Microbes are Essential for Life on
Earth: Have many important and beneficial
biological functions:
 Photosynthesis: Algae and some bacteria
capture energy from sunlight and convert it to
food, forming the basis of the food chain.
 Decomposers: Many microbes break down
dead and decaying matter and recycle nutrients
that can be used by other organisms.
 Nitrogen Fixation: Some bacteria can take
nitrogen from air and incorporate it into soil.
Important and beneficial biological functions of
Microbes:
 Digestion: Animals have microorganisms in their
digestive tract, that are essential for digestion, vitamin
synthesis, and overall health.
 Cellulose digestion (termites, cows, rabbits, etc.)
 Vitamin K and B synthesis in humans
 Prevent the overgrowth of pathogenic bacteria and yeast
 Medicine: Many antibiotics and other drugs are
naturally synthesized by microbes.
 Penicillin is made by a mold
Penicillin is Produced by a Mold
Important and beneficial biological
functions of Microbes:
 Food Industry: Many important foods and
beverages are made with microbes:
 Alcoholic beverages (Wine, beer, rum, whiskey)
 Bread
 Vinegar
 Soy sauce
 Cheese
 Pickles, olives, sauerkraut
 Yogurt
 Buttermilk
 Sour cream
 Coffee
 Chocolate
 Hams, sausages
Important and beneficial biological
functions of Microbes:
 Genetic Engineering: Recent advances in
gene splicing allow us to design recombinant
microbes that produce important products:
 Human growth hormone (Dwarfism)
 Insulin (Diabetes)
 Blood clotting factor (Hemophilia)
 Recombinant vaccines
Hepatitis A and B vaccines
 Human hemoglobin (Emergency blood substitute)
 Taxol (Breast and ovarian cancer)
 Erythropoietin (Anemia)
 Monoclonal antibodies (Disease diagnosis and
prevention).
Table 1.1 Some Industrial Uses of Microbes
Important and beneficial biological
functions of Microbes:
 Medical Research: Microbes are well suited
for biological and medical research for several
reasons:
 Relatively simple and small structures, easy to
study.
 Genetic material is easily manipulated.
 Can grow a large number of cells very quickly and
at low cost.
Short generation times make them very useful to
study genetic changes.
Microbes and Disease: Most microbes are
either beneficial or harmless to humans.
 Less than 1% of microbes cause disease.
 In 1962, the surgeon general of the United
States stated: “The war against infectious
diseases has been won”.
Today it is clear that this was overly optimistic:
 Emerging diseases: New diseases like AIDS,
hantavirus, Ebola fever, Lyme disease, Hepatitis C,
and others that did not exist a few years ago.
 Antibiotic and Drug Resistance: Many old
diseases are becoming resistant to traditional
therapies: Tuberculosis, gonorrhea, malaria, etc.
 Today infectious diseases cause ~25% of the
53 million worldwide deaths per year.
Leading Causes of Death Worldwide
2000 and 2011*
Source: World Health Org. 2013
Top Infectious Diseases Causing Deaths
Worldwide in 2010**
Disease
Cause
Deaths/year
Acute Lower Respiratory* Bacterial/viral/other
Diarrheal diseases
Bacterial/viral/other
AIDS/HIV
Viral
Tuberculosis
Bacterial
Malaria
Protozoan
Neonatal infection/sepsis Bacterial/viral/other
Meningitis
Bacterial or viral
Hepatitis
Viral (A/B/C/D)
Typhoid/Paratyph. fever Bacterial
Measles
Viral
Encephalitis
Bacterial/viral/other
Syphilis
Bacterial
Whooping cough
Bacterial
Tetanus
Bacterial
** Source: Lozano et al. Lancet 2012: 380: 2095-128
2,800,000
1,500,000
1,500,000
1,200,000
1,100,000
514,000
420,000
310,000
190,000
130,000
120,000
113,000
81,000
61,000
*Pneumonia, bronchitis, influenza, etc.
Neonatal tetanus kills thousands of infants every year.
Source: Tropical Medicine and Parasitology, 1997.
Microbes and Disease in Human
History
 Bubonic Plague (Black death): Several
devastating epidemics throughout history.
• High mortality: Up to 80% of those infected die.
• 1347-1351: Over 75 million died in Europe,
Asia, and Africa.
• Over 25% of population of Europe died.
• Cause was unknown for over 500 years, leading
to superstition, persecution, and hysteria.
• Bacterial disease transmitted by rat fleas.
• Rare today but still occurs:
• 10-15 cases/year in U.S.
• Last epidemic occurred in India in 1994.
Left: Swollen lymph nodes in bubonic plague infection.
Right: Infected flea bite with eschar and carbuncle.
Source: Tropical Medicine and Parasitology, 1997
Worldwide Distribution of Plague
++: Frequent transmission
+/-: Infrequent transmission.
Source: Tropical Medicine and Parasitology, 1997.
 Smallpox: One of deadliest human
infectious diseases throughout history.
• Caused by smallpox virus.
• First known case in 1175 B.C.: Egyptian
pharaoh Ramses V died from smallpox.
• Several hundred million deaths through history.
• Up to 90% of Native American population was
killed by smallpox and other diseases (measles
and plague) introduced during European
conquests.
• Native population of Central and South America dropped
from 130 million to about 1.6 million over several decades.
• Smallpox was used as a biological weapon by British
colonists in North America.
• 600,000 deaths/year in Europe from 1500-1700.
Smallpox infection in a small child.
Disease was eradicated worldwide by immunization in 1977.
Source: Microbiology Perspectives, 1999.
 Smallpox (Continued)
• 75% of survivors were severely scarred and/or
blinded.
• An effective vaccine was developed in 1870s by
Edward Jenner, using a related virus (cowpox).
• Smallpox was the first and only viral disease to
be completely eradicated (1977).
• Worldwide immunization campaign in 1960s.
• Only infects humans.
Tuberculosis (TB): Caused by a bacterium that
mainly infects lungs but may spread to other parts of
body.
• Leading killer of world’s infectious diseases:
• 3 million die worldwide every year.
• Over 1 million killed in U.S. between 1930-49.
• One out of three people infected worldwide.
• In U.S. 10 million people are presently infected, but only 5% will
develop active disease.
• Most healthy individuals can contain infection.
• Treatment: Antibiotics for up to one year or longer.
• After introduction of antibiotics, TB declined from 1950s to 80s, and
then started to increase again.
• Low patient compliance with treatment has caused antibiotic
resistant TB.
• AIDS epidemic has caused an increase in cases.
Tuberculosis is leading killer among infectious diseases
worldwide. Patient with lymph node necrosis.
Photo by Dr. I. Small
 Childbirth Fever: Common nosocomial
(hospital acquired) infection.
• Bacterial infection of the uterus as a result of
childbirth or abortion.
• Transmitted by hands and instruments of
physicians and midwives.
• Extremely common before the 1900s.
• About 1 in 17 women who gave birth would become
infected (fever, chills, delirium, and death).
• Cause was unknown.
• Austrian doctor Semmelweiss showed that washing
hands and instruments with a disinfectant solution
greatly reduced cases.
• Today common in women who have illegal
abortions, especially in third world countries.
 AIDS: Acquired Immune Deficiency Syndrome.
• First cases reported in 1981 at UCLA.
• Cause: Human Immunodeficiency Virus (HIV)
• Transmitted by sexual contact, blood transfusions, motherto-child, and infected needles.
• Destroys an individual’s immune system, making them
susceptible to many infectious diseases and cancer.
• Number of cases has grown rapidly during the last two
decades. As of 2010:
• Over 1’200,000 individuals live with AIDS in the U.S.
• Over 630,000 US AIDS patients have died
• Over 40 million deaths worldwide.
AIDS patients with wasting and Kaposi’s Sarcoma
Source: Tropical Medicine and Parasitology, 1997 and AIDS, 199
New HIV Infections in the United States, 2010
n = 49,273, CDC
History of Microbiology
Early Studies
Before 17th century, study of microbiology was
hampered by the lack of appropriate tools to
observe microbes.
 Robert Hooke: In 1665 built a compound light
microscope and used it to observe thin slices of
cork. Coined the word cell.
 Anton van Leeuwenhoeck: In 1673 was the first
person to observe live microorganisms which he
called “animalcules” (bacteria, protozoa), using
single-lens microscopes that he designed.
Antoni van Leeuwenhoek
Early Microbiology
Spontaneous Generation vs Biogenesis
 Before 1860s many scientists believed in
Spontaneous generation, i.e.: That living
organisms could arise spontaneously from
nonliving matter:
 Mice come from rags in a basket.
 Maggots come from rotting meat.
 Ants come from honey.
 Microbes come from spoiled broth.
Early Microbiology
Spontaneous Generation vs Biogenesis
 Theory of Biogenesis: Belief that living cells can
only arise from other living cells.
 Francesco Redi: In 1668 proved that maggots do
not arise spontaneously from decaying meat.
 Lazaro Spallanzani: In 1765 found that nutrient
broth that had been heated in a sealed flask would
not become contaminated with microbes.
 Some proponents of spontaneous generation argued that
boiling had destroyed the “life force” of air in flask.
 Others argued that microbes were different from other life
forms.
Francesco Redi’s Experiments
Spontaneous Generation versus
Biogenesis
Debate was finally settled by Pasteur.
 Louis Pasteur: In 1861 finally disproved
spontaneous generation when he demonstrated
that microorganisms in the environment were
responsible for microbial growth in nutrient broth.
Designed swan neck flasks that allowed air in, but
trapped microbes in neck.
Developed aseptic technique: Practices that prevent
contamination by unwanted microorganisms.
Pasteur’s experiments with “swan-necked” flasks
Steam escapes
from open end
of flask.
Infusion
is heated.
Air moves in
and out of flask.
Infusion sits;
no microbes appear.
Months
Infusion remains
sterile indefinitely.
Dust from
air settles
in bend.
History of Microbiology
Golden Age: 1857-1914
Rapid advances led to the development of
microbiology as a science.
Pasteur’s Contributions to Microbiology:
 Fermentation: Pasteur found that yeasts were
responsible for converting sugar into alcohol in
the absence of air.
Souring and spoilage were caused by bacterial
contamination of beverages.
Golden Age of Microbiology
Pasteur’s Contributions:
 Pasteurization: Developed a process in which
liquids are heated (at 65oC) to kill most bacteria
responsible for spoilage.
 Disease Causes: Identified three different
microbes that caused silkworm diseases.
 Vaccine: Developed a vaccine for rabies from
dried spinal cords of infected rabbits.
 Directed Pasteur Institute until his death in 1895.
Golden Age of Microbiology
Germ Theory of Disease: Belief that microbes
cause diseases. Before Pasteur, most people
believed diseases were caused by divine
punishment, toxic vapors, curses, evil spirits, etc.
 Agostino Bassi (1835): Found that a fungus was
responsible for a silkworm disease.
 Ignaz Semmelweis (1840s): Demonstrated that
childbirth fever was transmitted from one patient
to another, by physicians who didn’t disinfect their
hands. He was ostracized by colleagues.
Golden Age of Microbiology
Germ Theory of Disease: Microbes cause specific
diseases.
 Joseph Lister (1860): Used disinfectant to treat
surgical wounds, greatly reducing infection rates.
Considered the founder of antiseptic surgery.
 Florence Nightingale (1820-1910): English nurse
who introduced cleanliness and other aseptic
techniques into nursing practice.
Founded the first nursing school.
Golden Age of Microbiology
Robert Koch (1876): First person to
conclusively prove that a specific bacterium
caused a disease.
Koch Advanced Germ Theory: One microbe causes
one specific disease.
Koch studied the etiology of infectious diseases and
proved that:
Bacillus anthracis causes anthrax in cattle.
 Mycobacterium tuberculosis causes tuberculosis.
Koch Isolated and Studied Bacterial Pathogens
Bacterium 6
Bacterium 5
Bacterium 4
Bacterium 3
Bacterium 2
Bacterium 1
Bacterium 7
Bacterium 8
Bacterium 9
Bacterium 10
Bacterium 11
Bacterium 12
Koch’s Contributions
to Microbiology
– Developed Koch’s postulates: a series of
steps to identify bacterial pathogens
– Simple staining techniques
– First photomicrograph of bacteria
– Techniques for estimating bacterial counts
– Use of steam to sterilize growth media
– Use of Petri dishes to grow bacteria
– Aseptic techniques to transfer bacteria
– Bacteria as distinct species
Gram’s Stain
– In 1884 Danish scientist Hans Christian
Gram developed more important staining
technique
– Involves the applications of a series of dyes
– The Gram procedure is used to separate
into two groups:
• Some microbes are left purple, now labeled
Gram-positive
• Other microbes are left pink, now labeled Gramnegative
Gram-positive
Gram-negative
Results of Gram staining
History of Microbiology
Modern Microbiology: 20th Century
Chemotherapy: Treatment of a disease by using a
chemical substance. Chemical must be more
poisonous to microbe than host.
 Quinine: First known chemical to treat a disease
(malaria). Used by Spanish conquistadors.
 Synthetic Drugs: Made in the laboratory.
 Antibiotics: Produced naturally by fungi and
bacteria.
History of Microbiology
Modern Microbiology: 20th Century
 Paul Ehrlich (1910): Search for “magic bullet”.
Discovered salvarsan, an arsenic derivative, was
effective against syphilis.
 Alexander Fleming (1928): Discovered that
penicillin produced by the mold Penicillium
notatum was able to prevent microbial growth.
Penicillin was not mass produced until the 1940s.
 Rene Dubos (1939): Discovered two antibiotics
(gramidin and tyrocidine) produced by bacterium
(Bacillus brevis).
Modern Microbiology
Problems with Antimicrobial Chemotherapy:
 Side Effects
Toxicity: Damage to liver, kidney, bone marrow, teeth,
fetus, etc.
Dysbiosis: Destruction of beneficial microbes can cause
diarrhea, nausea, cramps, yeast infections, etc.
Allergic reactions: Anaphylactic reactions to penicillin,
rashes, etc.
 Drug resistant microbes: Multi-Drug Resistant Strains
Staphylococcus aureus (MRSA)
Tuberculosis (XDR TB)
Malaria
Diversity of Microorganisms
I. Bacteria (Sing. Bacterium)
 Small, single-celled (unicellular) organisms.
 Prokaryotes: “Before nucleus”.
Lack the following structures:
Nuclear membrane around DNA
Membrane bound organelles
Mitochondria
Chloroplasts
Golgi apparatus
Endoplasmic reticulum
Lysosomes
Kingdom Prokaryotae: Bacteria lack
nucleus and membrane bound organelles
Diversity of Microorganisms
I. Bacteria (Sing. Bacterium)
 Include two groups:
Eubacteria: Peptidoglycan cell walls.
Archaebacteria: Lack peptidoglycan cell walls.
 Shapes: Several forms:
Bacilli: Rod like. (Sing. Bacillus)
Cocci: Spherical. (Sing. Coccus)
Spiral: Corkscrew or curved
Square
Star shaped
Diversity of Microorganisms
I. Bacteria (Sing. Bacterium)
 Divide by binary fission (not mitosis).
 Source of nutrients varies:
Heterotrophs: Consume organic chemicals.
Autotrophs: Make their own food. Include
photosynthetic bacteria.
 Motility: Many can “swim” by using moving
appendages called flagella: Large whip-like structures.
 Distinguish between motility and Brownian
motion.
Diversity of Microorganisms
II. Fungi (Sing. Fungus)
 Eukaryotes: “True nucleus”
DNA is surrounded by nuclear membrane.
Cells have membrane bound organelles:
Mitochondria, endoplasmic reticulum, etc.
Cells are larger than those of procaryotes.
 May be unicellular or multicellular:
Unicellular: Yeasts
Multicellular: Molds, mushrooms
 Do not carry out photosynthesis.
 Absorb organic nutrients from their environment.
Fungi Include Molds and Yeasts
Diversity of Microorganisms
II. Fungi (Sing. Fungus)
 Source of nutrients varies:
Saprotrophs: Decomposers that feed on dead and
decaying matter. Most fungi are decomposers.
Parasites: Obtain nourishment by parasitizing live
animals and plants.
 Cell wall made of chitin.
 May reproduce sexually or asexually.
Diversity of Microorganisms
III. Protozoa (Sing. Protozoan)
 Eukaryotes: “True nucleus”
DNA is surrounded by nuclear membrane.
Cells have membrane bound organelles and are larger
than those of prokaryotes.
 Unicellular
 Sexual or asexual reproduction
 Classified based on locomotion:
Pseudopods: “False feet” (e.g. Amoeba)
Flagella: Long appendages (e.g. Trichomonas vaginalis)
Cilia: Small hair-like appendages (e.g. Paramecium)
Nonmotile: Do not move in their mature forms (e.g.
Plasmodium spp., causative agent of malaria)
Protozoa: Eukaryotic Unicellular Organisms
Diversity of Microorganisms
IV. Algae (Sing. Alga)
 Eukaryotes: “True nucleus”
 Photosynthetic: Important part of food chain
because produce oxygen and carbohydrates used
by animals.
 Unicellular or multicellular
 Sexual or asexual reproduction
 Cell walls composed of cellulose
 Found in aquatic environments (oceans, lakes,
rivers), soil, and in association with plants.
Algae: Simple Photosynthetic
Commonly Aquatic Organisms
Diversity of Microorganisms
V. Viruses
 Acellular infectious agents, not considered
living because they lack cells.
 Obligate intracellular parasites: Viruses can
only reproduce by using the cellular machinery of
other organisms.
 Simple structure:
Protein coat (capsid) with either DNA or RNA, but not
both.
May also have a lipid envelope.
Comparison of Cells and Viruses
Viruses Infecting a Bacterium
Virus
Bacterium
Viruses
assembling
inside cell
Diversity of Microorganisms
VI. Multicellular Animal Parasites
 Eukaryotes: “True nucleus”
 Multicellular animals, usually are visible to the
naked eye.
 Microscopic during some stages of life cycle.
 Spend part or all of their lives inside an animal
host.
 Helminths include:
Flatworms (Platyhelminths): E.g. Tapeworm
Roundworms (Nematodes): E.g. Ascaris, pinworm.
Parasitic Worm in Blood
Red blood cell