Introduction to
Microbiology
A Historical Perspective
Bio3124
Lecture 1
Objectives and reading
• Reading: Ch.1
• What is microbiology?
• History: How it came to be a field of study?
• Modern microbiology: day to day impact
on society
The Scope and Relevance of Microbiology
• importance of microorganisms
– first living organisms on the planet
• How many bugs are out there?
– live everywhere life is possible
– more numerous than any other kind of
organisms
– global ecosystem depends on their activities
(possess 50% of earth’s carbon and 90% of nitrogen)
– influence human society in many ways
Microbes and Microbiology?
• Microbes are living organisms
– Except for viruses, which are noncellular
– Metabolize energy, grow, reproduce
• Visualized by a microscope
• Unicellular , potentially exist independently
• simple in their construction; lack differentiated cells
and distinct tissues
• Microbiology: study of organisms too small to be
seen by the unaided eye (i.e., microorganisms)
• How small?
4
Size of Microorganisms
•Naked eye
• ~10 nm to 100 μm
• different type of optical system needed to resolve
• Where the bugs stand in the universe? Click here
Exceptions to the size rule
• Sulfur Pearl of
Namibia was
dicovered by Heide
Schultz
chemolitothrophic
G- bacterium
• 1000X larger than
bacteria (0.5-1 mm)
Thiomargarita namibiensis
(Pearl of Namibia)
Exceptions to the size rule
• Mimivirus: DNA virus
• 1.2 Mbp genome, ds linear
• 400-800 nm in diameter
• Infects amoeba
• Unique genes
Mimivirus
• Primitive life form?
Click to read more
The Microbial Tree
•
•
•
Difficult to classify
– Difficult to distinguish by shape
– Often reproduce asexually
– Pass DNA to each other horizontally
Use biochemical properties to classify
– Gram stain (G- and G+)
– Ability to metabolize different substrates (Bergey’s manual determinative
bacteriology)
Use DNA sequence to classify
– Microbial genomes are sequenced (click to link to database)
– Bacterial genomes are relatively small
– Genome = organism’s total genetic content
• Complete gene sequence known for many species
– Over 3000 bacteria, over >100 archaea
– thousands of viruses
• Microbes have greatest diversity of genomes
8
– Important for understanding evolution
The Microbial Family Tree
Carl Woese
 16s rRNA gene conserved
 Divergence reflects
relatedness
 Phylogenetic tree
 Microbial world in 3 domains
 Prokaryotes include 2 domains
 Domain of Eubacteria
 Domain of Archaea
 Eukaryotic domain
 Algea
 Fungi
 Protista
9
Microbes
• 6 major groups studied by microbiologists
• Cellular forms:
– Prokaryotes
• Archaea
• Bacteria
– Eukaryotes
• Algae

Protists

Fungi
• Acellular:
– Viruses
10
History of Microbiology
Old times…
• Humans knew how to deal with germs before even
knowing about their existence
۩ Storing food in cooler temperatures
۩ Salting, drying, smoking
۩ Use of spices
۩ Cremation of dead
۩ concealing and burying dead beyond a nearest
passing river or in a distant area
۩ traditional, mystical and superstitious explanations
Discovery of Microorganisms
 Antony van
Leeuwenhoek (16321723), the father of
microbiology
– a hobbyist microscopist
Dutchman
– first to observe and
describe microorganisms
accurately
Leeuwenhoek’s microscope
─ Composed of one lens
─ Light shines objects at a
45˚ angle
─ Worked like a dark field
microscope
─ Magnification: 50-300
fold
─ bright microorganisms
could be seen in a dark
bkg
Leeuwenhoek’s Observations
 Reported to the Royal
Society of London (1673)
 Accurate shape,
detailed movement
PMN
RBC
 Subjects were most
possibly bacteria and
protozoa and called them
“animalcules“
 also reported
Original blood smear image by Leeuwenhoek
structure
of
a and
human
sperm
Spirillum
as seen
by Leeuwenhoek’s
microscope
spermatozoa,
blood
cells
Note theTripartite
polymorphonuclear
cell
RBC
Check out a paper by Brian J. Ford about Leeuwenhoek
Few days of being
exposed to air.
Where do microorganism originate from?
Spontaneous generation??
The Conflict over Spontaneous Generation
• spontaneous generation
– living organisms can develop from nonliving or
decomposing matter
– publically a common sense vision with social and cultural
roots (almost 2000 years ago)
– Examples:
• flies from rotten meat and animal carcasses
• Mice from fungus infested grain barns
– Scientific methodology was not established
– What was the proof?
Jan Baptista Van Helmont
(1577-1644)
• A Flemish noble man, alchemist and
physician
• discovered carbon dioxide,
introduced the term gas in its
present scientific sense
• believed in spontaneous generation
• Paper by Louis Rosenfeld about Van Helmont
Jan Baptista Van Helmont
The Origin of life
(17th Centuray)
1579-1644
Adult mice
Spontaneous Generation
Could spontaneous
generation be true for
microorganisms?
Francesco Redi
(1626-1697)
• First blow to spontaneous generation
• Laying eggs is required for maggots and flies to come to
existence
• Supporters of SG: Life is necessary in order to bring about life
in certain cases!
John Needham
(1713-1781)
• Conclusion: Organic matter had vital force that confers
properties of life to non-living matter
• BUT: he had left the flasks unsealed after bioling
Lazzaro Spallanzani
(1729-1799)
Time
Microorganisms
Killed
• Air carries germs to broth and boiling kills the existing ones
• Supporters of SG:
• Compounds essential for generation of life were destroyed
by heating!!
• sealing prevents air that is necessary for spontaneous
generation
Louis Pasteur
(1822-1895)
Observations:
• John Tyndall: Organisms retained on cotton
filters resemble microorganisms in
contaminated foods
– Microorganisms are found in the air
– Microorganism in air settle on the surfaces
 Pateur’s
Swan neck
flasks could
supply air but
could also trap
ambient germs
from entering
broth
Pasteur Refutes the Spontaneous Generation
Pasteur Refutes the Spontaneous Generation
• ambient germs are necessary for promoting growth
• principle of sterility and aseptic work is important
Germ theory: Microorganisms Cause Disease
• For over 17 centuries the Galenism (Greek
physician 129-199 B.C.) was predominant
view for diseases according to which,
– Diseases are due to imbalances in 4
humors: blood, phlegm, yellow bile and
black bile
Relationship between Microorganisms and Disease
• Agostino Bassi (1773-1856)
– showed that a disease of silkworms was caused by a
fungus
• M. J. Berkeley (~1845-1852)
– demonstrated that the great Potato Blight of Ireland
was caused by a water mold
• Louis Pasteur (1822-1895)
– showed that the pébrine disease of silkworms was
caused by a protozoan Nosema bombycis
Other evidence…
• Joseph Lister (1827-1912)
– provided indirect evidence
– used diluted carbolic acid (phenol) to wash
surgical devices and wash wounds
– developed the principles of aseptic surgery
– his patients had fewer postoperative infections
– Disease frequency dropped in his hospital
Final proof…
• Robert Koch (1843-1910)
– established the relationship
between Bacillus anthracis and
anthrax
– used criteria developed by his
mentor Jacob Henle (1809-1895)
– these criteria now known as
Koch’s postulates
Read more about R. Koch. Check literature section
Microorganisms and Diseases
Robert Koch
Observations :
• The microorganism (Bacillus anthracis) is
found only in the infected animals and not in
healthy animals.
• Infected animals pass the disease to healthy
ones
• The microorganism found outside of the animal
could infect healthy animals
Germ theory: Koch’s postulates
Questions:
1. Can Koch’s Postulates be applied to
all microorganisms that cause
disease?
2. How can you apply Koch’s postulates
to viruses and viral diseases?
3. How can one apply Koch’s
postulates to non-cultivable
microorganisms?
The Development of Techniques for Studying
Microbial Pathogens
• Koch’s work led to discovery or
development of:
– agar
– Petri dish
– nutrient broth and nutrient agar
– methods for isolating microorganisms in pure
culture
The Pure Cultures and Isolation of Single Colonies
Koch :
Observation: Slices of potato when
exposed to air, will generate large
number of bacteria (colonies) of
different sizes, colours and forms
Colonies
Problem: Not all bacteria could grow on potatoes!
Solution :
Koch used gelatin as a
means for solidification of rich
culture media.
He formulated various culture
media
Disadvantages of Gelatin
• Gelatin liquefaction: It is digested by
various microorganisms eg. gelatinase
positive enterococci and streptomyces
• Low melting temperature: It is in the liquid
state above the temperature of 28oC.
Agar
• Polysaccharide derived from
the cell walls of a red algae
(Rhodophyta)
• A polysaccharide polymer that
contains 3,6-anhydrogalactose, 2O-methyl-α-l-galactopyranose and
6-O-methyl agarobiose
• Solid at >37oC.
• Melts at 100oC.
• Not digested by most bacteria
Gracilaria (red seaweeds)
Corollary to Germ Theory
• Stop germ transmission, stop disease spread
– Kill germ, prevent disease
• Antiseptics
– 1865: Aseptic surgery
» Joseph Lister
• Antibiotics
– 1929–1941: Penicillin
» Alexander Fleming
– Many newer antibiotics
– Bacteria become resistant
41
Corollary to Germ Theory
• Stop germ transmission, stop disease spread
– Stop spread of germs
• Epidemiology, public health measures
– Resistant individuals prevent spread of germs
• 1798: Vaccination with cowpox prevents smallpox
– Turkish physicians, Lady Montagu, Edward Jenner
42
Other developments…
• Pasteur and Roux
– discovered that incubation of cultures for
long intervals between transfers caused
pathogens to lose their ability to cause
disease (attenuation)
• Pasteur and his coworkers
– developed vaccines for chicken cholera,
anthrax, and rabies
Modern microbiology: day to day
impact on society
Microbes Shape Human History
• Food & Pharmaceuticals
• Bread, wine, cheese, Chocolate
– Can also destroy crops
• Hormones, antibiotics etc
• Microbial diseases change history
– 14th century: Bubonic plague (Black death)
caused by Yersinia pestis in Europe
– 19th century: Tuberculosis caused by
Mycobacterium tuberculosis
– today: AIDS by the human
immunodeficiency virus (HIV)
45
The golden age of microbiology (1857-1914)
• Many pathogens discovered
• Microbial metabolism studies undertaken
• Microbiological techniques refined
• A better understanding of the role of immunity
and ways to control and prevent infection by
microbes
Genetics and DNA Revolution
• Molecular genetics depends on bacteria
–
–
–
–
–
–
–
–
–
Concept of “gene” proposed for bacteria
DNA structure
Genetic code
Transcription, translation
Restriction enzymes
Recombinant DNA
Cloning
PCR reaction (watch the interview with Kery Mullis)
E. coli has best understood genome
47
The Future of Microbiology
Challenges and opportunities for future microbiologists
• infectious disease
• new and improved industrial processes
• microbial diversity and microbial ecology
– less than 1% of earth’s microbial population has been
cultured
More challenges and opportunities…
•
•
•
•
biofilms
genome analysis
microbes as model systems
assessment of implications of new
discoveries and technologies
• Stephen Jay Gould (1941-2002): “This is
truly the "age of bacteria" - as it was in the
beginning, is now and ever shall be.”