Start your study of the basic elements of germ theory with bacteria. Once you've inspected the anatomy of a bacterium cell and its function, explore how bacteria can cause disease and how they can adapt to make themselves elusive to your immune system. Then, investigate three diseases caused by bacteria: diphtheria, pertussis, and tetanus.

Zoom in to see a particle 100 times smaller than bacteria: the virus, which can replicate inside living cells. Follow the life cycle of a virus as you see what viruses like HIV and Ebola do to host cells. Meet two germs that fall between bacteria and viruses - the spirochete and rickettsia.

Although fungal diseases usually don't involve humans, they can indirectly affect us, and they have played a major role in human history. Investigate diverse infections that can be acquired when you come into contact with mold or fungus - sometimes by raking or blowing rotting leaves! Also learn if you should have your household duct system cleaned regularly.

Where would we be without the scientists that brought to life the inventions and discoveries that are the foundations of modern medicine? Meet some of the people who developed the tools to identify microorganisms, the means to pinpoint the source of a disease, the vaccinations to prevent them, and the drugs to treat them.

Trace the history of antibiotic development and explore how the eight classes of antibiotics attack bacterial infections. Gain an introduction to the increasingly important concern of antibiotic resistance, and learn how you can contribute to the more prudent use of antibiotics.