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Microbiology
Bacteria and Viruses
Germ Theory
Proposed by Scientist: Luis Pasteur.
Disease is caused by microscopic
organisms that invade the body
called pathogens (germs).
– Bacterial Pathogens (strep throat)
– Viral Pathogens (flu)
– Eukaryotic Pathogens (malaria)
– Fungal Pathogens (athletes foot)
Viruses
Classification: None
Viruses
Viruses are not alive.
– No cells
– They do not use energy like living things
– Cannot reproduce without a host cell
Consist of a protein coat and a piece
of either DNA or RNA
They exist only to infect and kill cells
Virus Types
All viruses function by injecting their
nucleic acid into a host cell and
taking over to create new viruses.
Lytic Viruses (Ex: Ebola)
Immediate takeover of the cell
Present in virulent (fast) viruses
– 1. Attach to cell
– 2. Insert viral DNA into host cell
– 3. Replicate viral DNA using host cell
– 4. Assemble new viruses
– 5. Destroy host cell to release new
viruses
End product is more viruses and a
dead cell
Lysogenic Cycle (Ex: HIV)
Delayed virus cycle; enter the host
nucleus and lie dormant for a while
– First two steps are the same as lytic
– 3. Insert viral DNA into host DNA
– 4. Viral DNA is replicated when host cell
divides
– 5. Virus enters the lytic cycle at any
time to kill the cell
*Can be manipulated for gene
therapy by replacing viral DNA with a
desired gene
Virus Cycles
DNA or RNA?
Viruses based on
DNA have no
problem invading
cells
– Polio
Viruses based on
RNA (called
Retroviruses) have to
use a protein called
reverse transcriptase
to turn their RNA into
DNA before they can
take over the cell.
– Mutate A LOT.
Evolve/Change rapidly
– Flu
Fighting Viruses
Because viruses actually hide inside the cells, it is
very hard to treat them with medication
Most viruses are killed by the immune system
without meds
– The best fight against viruses is prevention.
Vaccines can be given BEFORE a person is sick to
train them immune system to fight the virus
– Since viruses can only survive inside a host, it is
important that EVERYONE get vaccinated. If no
one can catch the disease, then the disease will
be gone forever.
Antibiotics do NOT work against viruses because
they cannot penetrate the human cell to reach the
virus. Antibiotics only kill bacteria.
Bacteria
Classification
– Domain: Archae or
Eubacteria
– Kingdom: Monera
– Cell type: single-celled
prokaryotes
– Feeding: some autotrophic,
some heterotrophic
– Reproduction: mostly
asexual by binary fission;
occasional sexual
reproduction for genetic
variability
Domain: Archaebacteria
Primitive bacteria
that live in harsh
environments.
3 types
– Methanogens
Live without oxygen
– Extreme halophiles
Live in extreme salt
conditions
– Thermoacidophiles
Love high
temperatures and/or
extremely acidic pH
Eubacteria
Modern Bacteria
classified by shape
and reaction to
Gram stain
–
–
–
–
–
–
Bacilli: rod
Spirilla: spiral
Cocci: round
Diplo: paired
Strepto: chains
Staphylo: clusters
– Gram Stain
Positive: purple
Negative: red
BACTERIA
Good Bacteria help you!
Non-pathogenic bacteria are helpful
– Nitrogen fixing bacteria put fertilizer
(nitrogen) into the soil for plants
– Gut bacteria help humans digest food
– Bacteria in the soil helps to decompose
and break down waste in the
environment
Pathogenic Bacteria
make you sick!
Antibiotics- medicine for treating
diseases caused by bacteria
– Interfere with bacterial cell walls
– Must be taken as directed
– Not effective against viruses
Antibiotic Resistance
Caused by using antibiotics too much
or incorrectly
– Bacteria evolve (by natural selection) to
resist the meds
New methods or different antibiotics
must be used.