Lesson 9: Bacteria Facteria

First we’ll need to create a home where bacteria will like to grow…and, as we learned in the last lesson, it must provide plenty of food.  If you ordered prepared petri dishes, use them for this experiment.  Otherwise you can make some food for your bacteria in this way:

Mix two envelopes of unflavored gelatin, two cups of cold water, two beef boullion cubes, and four teaspoons of sugar in a small saucepan.  Heat slowly to boiling, stirring constantly. Allow your homemade bacteria food to cool slightly.  Pour it out into small, shallow containers – like foil cupcake liners – until each container is about one-third full.  Cover the containers and place them into the refrigerator until the gelatin mixture is solid.  Be careful not to touch the gelatin.  

Now it’s time to add the bacteria.  To collect a specimen, swab a clean Q-tip over a surface you’d like to test (like a doorknob, a light switch, or the inside of the kitchen sink).  Lightly swab the Q-tip over the surface of the prepared gelatin.  Use a different collection site for each container.

Place each container into a separate ziplock bag.   Place the containers in a warm place for several days. Watch for white or colorful bacterial colonies to grow on the surface of the gelatin.

 This top photo is a swab from inside the      kitchen sink after three days.  The bottom photo is a three-day swab of the computer keyboard. The one below is the same keyboard swab after a week.

 

 

 

 

 

 

Here’s a swab of the inside of a healthy human nose after a week:  Pretty amazing, hunh?

 

Now let’s go back and check out the jars you prepared in the last lesson.  Remember, we wanted to see if chilling, pickling, or salting food was the best way to slow the growth of bacteria. Well, the cloudier the liquid the more bacteria are present. Find a bold sheet of newsprint.  Hold it behind the jar labeled “control”.  The liquid should be fairly cloudy and the type will likely be difficult to read through the liquid, because lots of bacteria had a chance to grow here. Now compare what you see through the control jar to what you see through the refrigerated, salted, and pickled (vinegar) jars.  They should all be less cloudy than the control…which method of retarding bacterial growth works the best?

USE THESE FLASHCARDS to help you study for the next test.  Click  “start study session”, and then “random” order and the”definition then term” option before you begin.  Then hit “flip card” to check your answer, and “next card” to advance to the next question. Email me when you are ready for the test!