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Chapter 18
VIRUSES
&
BACTERIA
Microbiology
Viruses
&
Bacteria
History of Microbiology
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1668
Redi disproves spontaneous generation
1675
Leeuwenhoek describes bacteria
Jenner 1798
• Makes small pox vaccine (1st
vaccine) used cowpox virus.
• 1818-1865
• Semmelweis Made connection
between disease and
cleanliness.
PASTURE
• 1860
• Discovered cause of
fermentation (yeast)
• Disproved spontaneous
generation.
Pasture
• Organisms can be carried by air.
• Cure for silk worm disease.
• Helped develop resistance for
fowl cholera.
Pasture
• Immunization for Anthrax.
• Rabies Vaccine.
Koch 1876
• Germ theory of disease.
• Koch’s postulates.
• Discovered microbes grow best
on a solid in colonies.
Koch 1876
• Developed AGAR.
• Assistant: Petri invented the
Petri dish.
Koch’s postulates:
• 1. Microbe is present in all
cases of the disease.
• 2. Isolate the microbe and grow
in pure culture.
Koch’s postulates
• 3. Pure culture put back into
test animal to cause the disease.
• 4. Take it out of the 2nd host,
isolate and identify.
Lister 1878
• Developed antiseptic surgery.
• Used phenol on everything.
Beijerinck 1880
• Discovered nitrogen fixing bacteria.
• N2 to NO2
Iwanowski 1892
• Transferred tobacco mosaic
virus into healthy tobacco plant,
plant became sick.
Gram 1884
• Developed ways to stain
bacteria.
• Gram +
• Gram • All bacteria fit into these two
categories.
Loeffler & Frosch 1898
• Studied Hoof and Mouth
Disease.
• Determined that a virus was
smaller than a bacteria.
Ehrlich 1910
• After 605 failures discovered
Drug # 606.
• Used as 1st real drug.
• Used to cure Syphilis.
• Organic Arsenic.
d’ Herelle 1917
• Discovered Bacteriophage.
• Agent (virus) that eats bacteria.
Fleming 1928
• Discovers penicillin from mold.
• One of the greatest medical
discoveries of all time.
• Kills bacteria.
Interesting note:
• By 1997 some bacteria have
evolved to the point they are
completely immune to ALL
antibiotics.
Stanley 1935
• 1st American to distinguish
himself as a microbiologist.
• Purified viruses, showed what
they were.
• TMV.
Thomas D. Brock 1966
• Discovers the first Organism
living in water that is near
boiling!
• Names it Thermus aquaticus
• Key to PCR technique.
Dr. Carl Woese
1977
• Proposed that a new Domain be
created for extreme bacteria.
• Name of Domain: Archaea
What is a Virus???
Viruses
• A virus is about 1/2 to 1/100th
the size of the smallest
bacterium.
• Most scientists consider them
non living.
Viruses
• Come in many shapes and sizes:
– Polyhedral
– Enveloped polyhedral
– Helical
– Enveloped Helical
– Complex
Why non living?
• Viruses DO NOT exhibit all 7
characteristics of life.
• Cells ………no
• Organization……Yes
• Energy Use…….only in host
• Response…….Yes
Alive or Not???
• Growth……….Yes in host
• Reproduce…….Yes in host
• Adaptation……..Yes
What do viruses do?
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Cause disease
Influenza
Aids
Measles
shingles
warts
colds
HIV
What do viruses do?
• Used in Genetic Engineering.
2 Main Kinds
• Virulent: Immediately cause
disease.
• Temperate: Does not cause
disease immediately.
4 Classes of Viruses
• RNA
• DNA
• Viroids
• Prions
RNA Viruses
• Nucleic acid is RNA
• Mutate more often than DNA
viruses.
• Enter the cell and produce
proteins right away using hosts
ribosomes.
EXAMPLES
• Polio
RNA retroviruses
• Use enzyme reverse
transcriptase to make DNA
from RNA.
• New DNA makes new RNA
then proteins.
EXAMPLE
• HIV/AIDS
DNA viruses
• Once in a cell the DNA makes
new RNA and then proteins.
• Splices it’s DNA into a celss
DNA then produces new
proteins.
EXAMPLES
• Pink-eye
Viroids
• Short single strand of RNA, free floating.
• Not long enough to make a full protein.
• Usually interferes with normal cell function.
Prions
• Glycoprotein particle containing about 250
AA.
• Associated w/ diseases that have a long
incubation period.
• KURU degenerative nerve disease in
humans.
The Bacteriophage
Anatomy of a Bacteriophage
The Lytic Cycle
• T2-T4-T6-T8….
• Lytic phages explode host cell
to get free.
Lytic Cycle
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Five phases:
Absorption
Entry
Reproduction
Assembly
Release
Absorption
• Virus attacks host.
• Tail fibers contain chemicals
that are attracted to the surface
of the cell.
Entry
• Virus releases an enzyme that
weakens the cell wall.
• Tail contracts
• base plate perces the cell wall
• DNA or RNA is injected into
the cell
Replication
• Viral DNA takes complete
control of cell activity.
• They direct the cell to make
viral DNA, proteins, and Parts.
Assembly
• Proteins coded for by viral
DNA act as enzymes that put
the new virus parts together.
• This continues until cell is
completely stuffed with new
viruses.
Release
• Viruses release an enzyme that
digests the host cell wall (lysis)
allowing the new viruses free to
start the process over again.
Lysogenic Cycle
T1-T3-T5-T7 etc.
Lysogenic Cycle
• Temperate viruses go though
this process.
• DNA injected into cell.
• DNA is incorporated into the
host cells DNA (prophage).
• Host cell lives normally.
• Host cell divides, usually many
times.
• Each new cell has viral DNA in
it now.
• Usually the prophage within each
host cell lays dorment until
triggered by something.
• Replication
• Assembly
• Release