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Backup data for failed experiments

Information for planning dilutions to be used for artificial contamination (equations, titers, pretrials)

View results of actual hand washing experiment

Examine variation in the outcome of antibacterial soap trials

Introduction to Microbiology

Bacterial cultures


Eschericia coli bacteria (c) Dennis Kunkel

In order to observe individual bacteria, they must be observed at high magnification under a light microscope or a scanning electron microscope.  A liquid culture bacterial culture appears cloudy due to the scattering caused by the millions of bacteria.

When a liquid bacterial culture is centrifuged in a microcentrifuge, the pellet may appear as a small white smear on the side of the tube near the bottom of the tube.  

When a bacterial culture is plated on solid medium, the invisible bacteria grow into visible colonies.  The color and shape of the colonies are characteristic of the species of bacteria.  


Individual E. coli colonies


Dense and overlapping E. coli colonies


Each circular colony is the result of growth of an individual bacterium in the culture that was plated.



When the titer of the culture is very high, colonies merge into a single lawn.  Notice that the lawn is translucent, in contrast to the nearly transparent agar.  The edge of the lawn is visible near the edge of the plate.

To view more great electron microscope images, click on the image below: