Download Pathogens

Pathogens
Pathogens are living things that cause illness. There are two main classes of pathogens that infect
humans: bacteria and viruses. Bacteria cause illnesses such as food poisoning, strep throat, and
pneumonia. Viruses cause illnesses including the common cold, influenza (the flu) and HIV/AIDS.
One of the main differences between the two pathogens is that antibiotics can be used to treat
bacterial infections, but antibiotics do not have an effect on viral illnesses. You can however get
vaccinations to protect from various viral infections. Vaccines are most effective if received when
young and prior to infection. Another difference between bacteria and viruses is that some
bacteria can be beneficial to humans. You have a lot of bacteria living in your body that help
digest food, get rid of waste and fight off bad bacteria.
Pre-Lab Questions
1. Think of the last time that you were sick. Write down your symptoms or how you felt.
2. Do you know whether you had a bacterial or viral infection (or something else)?
3. How do you take care of yourself when you get a cold?
4. Name one way that bacteria help you.
In this experiment, we will see what happens to the bacteria and viruses in your body when you
take antibiotics. We will use candies to represent pathogens. Choose a color for each organism:
Color
helpful (good) bacteria
pathogenic (bad) bacteria
viruses
Experiment #1
You go to the doctor with a fever and a sore throat. She does a test and determines that you
have strep throat (caused by the bacterium streptococcus pyogenes). Take 25 red candies to
represent the pathogenic bacteria (streptococcus pyogenes) and 25 blue candies to represent
your natural good bacteria. The number of bad bacteria is too large for the good bacteria to
fight off, so your doctor prescribes an antibiotic medication to take for 10 days.
Procedure
1. Record the number of bacteria you start with in your data table for Dose 0 (before you
take any antibiotic).
2. Place all of your bacteria (candy) in a cup, shake, and then pour out onto the table. This
shake is equivalent to your taking your antibiotic for one day.
3. Any bacteria without the white letter showing have been killed. Record how many of
each color are still alive in your data table. Remove the dead bacteria and put the live
ones back in the cup.
4. Repeat the shake process 9 more times to represent taking the antibiotic for 10 days.
5. Answer the questions below. If there is time, graph your results.
Antibiotic Dose
Number of pathogenic
bacteria
Number of Helpful Bacteria
0
1
2
3
4
5
6
7
8
9
10
Questions
1. How many days of taking the antibiotic were required to kill all of the pathogenic (bad)
bacteria?
2. Sick people usually start to feel better after a couple of days on an antibiotic, even
though some of the pathogenic bacteria are still there. How many pathogenic bacteria
are still there after three days?
3. Why is it important to take all of the antibiotic prescribed?
4. Did any of your good bacteria survive the antibiotic?
5. Often times people get an upset stomach after taking antibiotics because all of the good
bacteria are gone. Do you know any ways to help regrow your good bacteria?
Experiment #2
Your friend Dan goes to the doctor with a runny nose and a headache. She tells Dan that he has
a cold, and that rest and lots of fluids are the best way to treat the cold. Dan ignores her advice
and takes some antibiotics that he had left over from a previous illness. Take 5 red candies to
represent pathogenic bacteria, 20 blue candies to represent good bacteria and 20 green
candies to represent virus particles.
1. Make your own data table and record the number of bacteria you start with in your
data table for Dose 0 (before you take any antibiotic).
2. Place all of Dan’s bacteria and virus (candy) in a cup, shake, and then pour out onto the
table. This shake is equivalent to Dan taking an antibiotic for one day. Any bacteria
without the white letter showing have been killed. Viruses are not affected because
antibiotics don’t kill viruses!
3. Record how many of each color are still alive in your data table. Remove the dead
bacteria and put the live ones and the viruses back in the cup.
4. Repeat the shake process 9 more times to represent Dan taking the antibiotic for 10
days.
5. Graph your results and answer the questions below.
Questions
1. How many viruses were left after Dan took the antibiotic for 10 days?
2. Do you think that Dan felt better after taking the antibiotic? Why or why not?
3. After taking the antibiotic Dan develops a new symptom – a stomach ache! What do you
think caused the stomach ache?