Day 2 Handout

Bacteria are everywhere.

• w or w/o oxygen
• extremely hot or cold environments
• tissues of animals and plants

Bacteria are very different from one another.

• cellular structures (wall)
• size and shape
• growth rate and conditions (temperature, oxygen, food sources)
• ability to produce chemical weapons (antibiotics)
• suceptibility to antibiotics or other antimicrobial agents

Microbiologists want to study the characteristics of each individual kind of bacteria separately. That's what we want to do. How do we do this? Environments have a complex mix of bacteria. One organism is very small (.001-.005 mm). We need to get a whole bunch of organisms that are exactly the same. Today we are going to streak for isolation of a pure culture of one kind of bacteria.

1. We'll examine the plates from yesterday (lawn, dots, nothing). Those with nothing think about why this might be, share with another member of your lab group.
2. Use sterile loop to touch only one spot on the plate. Your group leader will demonstrate how to streak for isolation. The spot where you touch will have millions of bacteria. You goal is to spread the bacteria on the plate so that by the end there are spots on the plate with only one organism. When we incubate the plates at 30, the organism will divide into two identical organsims, and these will keep dividing until there is a colony (which looks like a spot on the plate) made up of millions of bacteria that are exactly the same.
3. Now, a pure culture can be used to learn about the characteristics about one kind of bacteria. Later this week we will study the cell wall and suceptibility to antibiotics.
4. Today we will practice examining bacterial characteristics with a special plate called MacConkey agar that you will streak the same way. Looks reddish purple. Growth on this plate will give us information about the kind of cell wall and whether the organism can ferment the sugar lactose. We'll analyze the results on Thursday.