Name: ______

Date: ______Period: ______

Microorganisms Everywhere

Although we can’t always see them, microorganisms are present in almost all environments. Many can be grown in the laboratory on plates containing a solid, nutrient-rich medium (agar plates). After several days, a single bacterial cell grows into a population of bacterial cells that is visible to the naked eye. This population of cells is called a microbial colony. In this exercise we will test for the presence of microorganisms on our hands and on objects we are in contact with.

Materials

Sterile agar plates (1 per student)

Objects of your choice to test for the presence of microorganisms

Q-tips (to get bacteria from teeth, sandwiches, fruit juice, etc.)

Toothpicks

Instructions

Wednesday

  1. Get an agar plate and label it on the bottom with your name and the date and the objects that you are going to test for microorganisms. This agar plate is sterile – it has been heated and no bacteria are on it. KEEP THE LID ON IT!!! Divide your plate into four sections by drawing lines on the bottom of the plate. Choose which objects are going to be in which quadrants and record below.

I: ______

II: ______

III: ______

IV: ______

  1. Get your Q-tip wet (with saline solution). Swab the object you want to test for bacteria.You can also use a toothpick if you want.
  1. Open the cover of the plate and gently press your object on the surface of the agar. Be careful not to press too hard – you don’t want to press through the agar. Make sure to label what object you used in each section.
  1. Cover the plate as soon as you remove your object or the Q-tip or the toothpick. You want to have the lid open for as little time as possible so microorganisms from the air do not fall on the plate.

Friday

  1. Record what happened on your plate.
  2. Sketch your plate. Label your drawing so that you know what objects the colonies came from.

1.2.Record size, color, texture, and shape of colonies.

I / II / III / IV
Object Sampled
Size of Colonies
Color of Colonies
Texture of Colonies
Shape of Colonies
Other Observations about Colonies

2. Prepare samples of the microorganisms on your plate by using the methyl blue staining method.

2.1. Place a few drops of stain on the slide.

2.2. Use a toothpick to smear some of the bacteria from one colony on the slide and mix it into the stain. You should take only enough bacteria to cover the tip of a toothpick – definitely not more! If you take too many cells, you won’t be able to see them clearly under the microscope.

2.3. Carefully place the cover slip over the bacteria.

3. For each sample, examine it under the microscope and draw the bacteria. You will need to use the highest magnification on the microscope to see the bacteria. Make sure you record which colony it came from. If you find a well-stained sample, take it to the videomicroscope so that everyone can see it.

  1. On your plate, you used many different objects to grow bacteria. Do some of the bacterial colonies look similar? If so, why do you think this is?
  1. If some bacterial colonies look very different from one another, why do you think this is?

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