1. Viruses, Bacteria and Germ Theory
Unit 11
Viruses, Bacteria and Germ Theory

2. Germ Theory of Disease
Throughout history, people have created many explanations for disease.
The introduction of the germ theory led to the understanding that many diseases are caused by microorganisms (viruses and bacteria).
Two important experiments by Pasteur and Koch led to an understanding of the presence of microorganisms and their relationship to diseases

3. Boiled Broth Remains Sterile
Pasteur
Invented Pasteurization – heat liquids to kill bacteria.
Experiment showed that life cannot arise from nothing (disproving Spontaneous Generation)
Boiled Broth Remains Sterile
Exposed pasteurized broths to air in swan-neck flask with a tube that wouldn’t allow dust particles to pass.
Nothing grew unless flasks were broken open.
Showed that microorganisms came from outside (spores on dust), not spontaneously generated in broth.
Curved Neck Removed
Micro-organisms Grow

4. Causes disease in healthy animal
Koch
Developed Koch’s Postulates – a test to see which microorganisms cause a specific disease
The disease causing organism must be –
Diseased Animal
Causes disease in healthy animal
Same Pathogen
Re-cultured
Cultured Pathogen
Found in all cases of disease
Removed and grown in laboratory
Injected into a healthy organism to cause the same disease
Match the original sample when removed from organism #2

5. Germ Theory of Disease
Acceptance of the germ theory has led to modern health practices.
Aseptic (sterile) techniques to keep germs out of the body
Development of vaccinations and antibiotics to prevent and fight disease
Safe handling of
food and water
Sanitation
Death rate for mothers during childbirth 
What happened in early 1900s?

6. Unit 11
Viruses

7. Viruses Viruses are NOT alive. Basic Structure:
Not made of cells
Need a host to reproduce
Basic Structure:
Protein Coat
Nucleic Acid Core (DNA or RNA)
Very small – About 100X smaller than a bacteria
Can only be seen with electron microscopes

8. Viral Replication
1. The virus attaches to a cell and injects DNA.
3. New viruses are made.
2. Viral DNA takes over protein synthesis.
4. The cell breaks open and releases viruses.
Viruses need a host cell to transcribe and translate their genetic material. They cannot reproduce without a host.
Some viruses insert genetic material into the host’s DNA, then remain dormant and reproduce later. (Chicken Pox  Shingles)

9. Viral Diseases
Common cold, the flu, rubella, mumps and measles, smallpox, hepatitis, polio, HIV/AIDS, and rabies
Prevention:
Vaccines: Weak or inactive virus injected into body
This makes your immune system create antibodies so it can recognize and fight off the virus if you are exposed to a full version later
Treatments:
Some anti-virals
NOT antibiotics! (which only work on bacterial infections)

10. Unit 11
Bacteria

11. Bacteria Prokaryotic Cells (small, simple, no nucleus)
Most abundant life forms on Earth.
They can survive in many environments.
Bacterial Cell Structures:
Cell wall
Cell membrane
Cytoplasm
DNA
Ribosomes
Pili (attach to other cells)
Flagella (movement)

12. Bacterial Shapes
Bacillus Rods
Coccus
Spheres
Spirullum
Spirals

13. Bacterial Diseases Plague, cholera, cavities,
dysentery, typhoid fever,
MRSA, acne
Treatment:
Antibiotics – kill bacteria by affecting things that bacteria have but humans do not.
The first antibiotic discovered was called penicillin in 1929.
Some bacteria have evolved to become resistant to antibiotics.

14. Examples of Good Bacteria
Environment: Many bacteria act as decomposers to recycle nutrients to the soil
Digestion: E. coli helps us digest our food
Food/drink: Bacteria help with fermentation to make cheese, vinegar and alcohol
Medical: Manufacturing insulin that is used to treat Diabetes

15. How Bacteria Obtain Energy
Two major categories:
Autotrophs - Make their own energy - 2 types
Phototrophic autotrophs - Get energy from sunlight
Chemotrophic autotrophs - Get energy from
inorganic molecules (eg. Sulfides)
2. Heterotrophs - Energy obtained from other
organisms
Chemotrophic heterotrophs - obtain energy by
dissolving/absorbing organic material
Phototrophic heterotrophs - meet some energy needs
from photosynthesis, but must absorb organic
compounds.

16. Bacterial Reproduction
Bacteria reproduce through binary fission.
Can engage in primitive sexual reproduction
called conjugation.
A bridge is formed between 2 bacteria (pili)
Plasmids are shared across bridge, thus
exchanging genetic information.
In times of harsh conditions, bacteria can
form endospores, to encapsulate themselves
in a dormant state, until conditions improve.