Descriptions of Infectious Agents

Bacterial Growth Experiment

BACTERIAL GROWTH EXPERIMENT 

Today we are going to see how bacteria (germs) grow by using petri dishes. These are special dishes that have a tannish colored medium, called agar, in them to help the bacteria grow.

Some things to remember when collecting your sample:

 

Choose an area that you would touch with your hands – give examples (primary students will use their fingers on the agar to collect the bacteria).

Do not touch the agar.

Use a clean Q-tip to collect the bacteria by rolling the Q-Tip on the surface and turning it (demonstrate). The bacteria are now on the Q-Tip; do not touch the Q-Tip with your hands.

Streak the agar plate with the Q-Tip in a tic-tac-toe pattern (demonstrate).

Do not pole the Q-Tip into the agar; it will make a hole which makes it harder to see the bacteria grow.

Put the lid on the agar plate and tape the sides shut so that you bacterium does not get out (demonstrate).

Mark the tape with your grade, teacher, and what surface you used to collect the bacteria.

With the help of a teacher, place the petri dish in the grow lab*.

*The temperature in the grow lab should be around 37 C (98 F)

 

Here you explain that scientists use C, not F, and how to convert from F to C (C X 2 - 10% + 32 = F).

A bacterium doesn’t grow when it is too cold (less than 40 F); that is why we use refrigerators to keep our food fresh.

A bacterium doesn’t grow when it is too hot (over 140 F); surgeons sterilize their tools to kill any bacteria or bacteria would be on our skin and it would get infected.

Bacteria grow well when it is close to our body temperature of 98 F, so we try to keep the lab at around 37 C.

***In the morning you will look at the petri dishes and record what you see (show form to use).

Reminder- DO NOT TOUCH THE PETRI DISHES

There may be condensation, water droplets, collected on the dishes – explain condensation.

 

***Here’s what we are going to do:

Break into groups of 4 or 5.

Each group decides on a place in the school to collect the bacteria – find a place where our hands would be that might have germs.

Again demonstrate and tell how to collect bacteria and where it is to be put.

It may take 2 or 3 days for the bacteria to grow on the petri dishes.

***You will be doing a hypothesis – an educated guess – about the bacteria you collected.

 

***Demonstrate again how bacteria is spread – someone spits, someone else steps on it, then walks on the floor, someone sits on the floor, touches it with their hand and then puts hand in mouth.

 

 

Germ Potion Experiment

Open the headline to see the Invisible Germs Discovery to reinforce the necessity.

 

Before doing this experiment, please review the proper hand washing technique with your students using Henry the Hand’s Hand Washing Guide.

 

The technique is as follows:

1. Use SOAP AND WARM RUNNING WATER.

2. Rub your hands vigorously for AT LEAST 20 SECONDS.

3. Wash all surfaces including back of hands, wrists, between fingers, under fingernails.

4. Rinse well (leaving soap on your hands will lead to drying & cracking).

5. Dry hands well with paper towel.

6. TURN OFF THE FAUCET WITH THE PAPER TOWEL you used to dry your hands (this prevents picking up the germs that were on your hands when you turned the faucet on).

 

The kit can be used three ways: hand washing training, demonstration of cleaning surfaces, and spreading germs from one person to another. Divide the class so that ½ are doing surface cleaning and half are doing “germ” spreading. This will allow for discussion between students as they share results.

 

            HAND WASHING: Place a few drops of solution on each student’s hands. Have the students rub it in like hand lotion. This will spread the “germs” all over the hands. Have the students wash their hands as described above. As the students wash their hands, use the fluorescent lamp to highlight where they miss (the black light will make the “germs” glow brightly). This should demonstrate the importance of washing your hands correctly. You may want to divide the class further and have some students wash their hands incorrectly at first to show how the germs will remain (i.e. using water only or not rubbing hands vigorously).

 

            SURFACE CLEANING: Use the Glo-Germ powder. Shake a small amount onto a table(s) and lightly dust the entire area. Have the students clean the entire surface until all visible powder is gone. Use the fluorescent lamp to highlight the “germs” that were missed.

 

            SPREADING OF GERMS: Shake a small amount of powder on students’ hands. Have students rub powder all over hands and then shake hands with several other students who do not have the powder on their hands. Also have students touch other surfaces and each other. Use the fluorescent lamp to highlight the “germs” that were transferred.

 

Definitions

GERMS
   Germs are microorganisms, tiny living things that can only be seen with the help of a microscope. Billions of microorganisms live on your skin or in your body. Most of them are harmless; some actually help keep you healthy. Disease germs (which scientists call pathogens) are the exception. They are specific microorganisms which are capable of causing contagious diseases.
   Scientists have classified pathogens into six categories: viruses, bacteria, rickettsiae, fungi, protozoans and parasitic worms. Viruses and bacteria are the disease-causing agents of most childhood infections and the ones most relevant to primary grade school children.  

VIRUSES

   Viruses are smaller than any known cell. They are composed primarily of protein and nucleic acid, the genetic material responsible for determining the growth of cells in living organisms. Many of the viruses that have been identified are classified as pathogens, that is, capable of causing illness. Viruses can only multiply when they invade cells. Once inside a cell, a virus can cause disease by changing the normal chemical activity of the cell. The virus directs the cell to reproduce viruses. Once full of viruses, the cell bursts, spreading the new viruses to other cells where the process begins all over again. Viruses are responsible for more diseases than any other type of pathogen. Each different virus causes a specific disease.
   Examples include the common cold, influenza and most contagious childhood infections such as chicken pox, measles, mumps, cold sores and fever blisters. Scientists also suspect that viruses may be responsible for certain forms of cancer.  

BACTERIA

   Bacteria are single-celled organisms that have one of three basic shapes: rods (bacilli), round (cocci) or spiral (spirilla). Bacteria can grow and reproduce quickly by doubling in size and splitting in half. Bacteria can be found throughout the environment. You come into contact with them on almost everything you touch. Millions of bacteria are also normally present on and in the body. Most don�t cause problems and many help with the normal functioning of the body. For example, in the intestines, some bacteria help process body wastes for elimination. Other bacteria, however, are pathogenic. Pathogenic bacteria that live inside the body obtain food for the substance found in human tissue. They can cause disease when they produce specific products such as tetanus or other toxins that poison the body.
   Examples of diseases caused by bacteria include strep throat, pneumonia, diphtheria and tetanus. Pathogenic bacteria can also multiply in food that is improperly stored and can cause food poisoning.

Lab sheet for Results

Print off this lab result sheet to document your observations. Thank you for your effort to teach others.

Sniff Test

Here is a great experiment to see how effective are your olfactory senses(nose). Take many differing types of products with different scents and blindfold your vlounteers to test their ability to identify the products by the smell. Examples are food products, perfumes, old tennis shoes, gym bag and other items around the house. DO NOT use clorox or bleach as it is TOO STRONG and can damage the olfactory senses.

    Then use an unwashed hand and washed hand to "smell" the difference. "If they do not smell clean, they probably are not."  

Micro Droplet Dispersion and Spread

Utilize an atomizer(spray bottle) to simulate a cough or sneeze demonstrating how droplets are dispersed from the mouth and nose landing on the next surface by gravity. Then they lay there wauting for the next hand to "pick up" and carry someplace. Use glow powder or simply glitter on surfaces then watch how it is spread by our hands.

  Take a picture with the sunlight shining through the "spray" for a great visual demonstration.