Grades 10 - 12
This lesson begins with the elementary understanding most people
have of microbial diseases. Using the video as a starting point, students
should expand their understanding of infectious diseases including the means
of transmission, treatment, and prevention. Students will grow cultures
of Staphylococcus aureus; and by observing the bacteria under the oil emersion
lens of the microscope, will estimate and graph the Staphylococcus aureus
count for their own bodies and those of the entire class.
READING RAINBOW #34: Germs
Students should be able to:
- Explain the basic concepts of microbial infectious diseases including
their transmission, treatment, and prevention. Grow a bacterial culture
of Staphylococcus aureus.
- Perform the Gram Staining procedure and then look at the bacteria
they have grown using the oil emersion lens on a microscope.
- Count the number of bacteria they have grown and use this data to
extrapolate the number of bacteria growing in their body.
- Develop a raw data table of the number of bacteria present in each
member of their class.
- Calculate the mean number of bacteria present in their class.
- Graph the number of bacteria present in their class.
Supplies are available from any of the biological supply companies.
I recommend putting students in groups of two. For each pair the following
- 1 individually wrapped sterile cotton swab
- 1 pair of latex gloves
- 1 Mannitol salt agar plate
- 3 or 4 paper towels
- 1 glass slide
- 1 Bunsen burner
- 1 inoculating loop
- tap water
The following stains (crystal violet, Gram decolorizer, Gram iodine, and
safranin O) come in 250 milliliter bottles. It is ideal to have one set
of stains per group; but if funding is limited, two sets will serve a class
- Crystal violet, Gram decolorizer, Gram iodine, safranin O.
- A microscope with an oil emersion lens is needed to see bacteria.
The more microscopes the better.
- A bottle of emersion oil (mineral oil works).
- 1 refrigerator to keep the agar plates in before the lab.
- 1 autoclave or 10% bleach/water solution for disposal of the agar
plates that have grown bacteria.
- 1 incubator.
Virus - single or double strand of either RNA or DNA.
Viruses do not exhibit the characteristics of living organism; therefore,
they are not considered to be alive.
Bacteria - the smallest living organisms.
Bacilli - rod-shaped bacteria.
Cocci - round-shaped bacteria.
Spirilli - spiral-shaped bacteria.
Staphylo - prefix for clumps of bacteria.
Strepto - prefix for chains of bacteria.
Pathogenic - disease causing carriers-individuals who transport a
bacteria but do not get sick from it.
Nonpathogenic - not disease causing.
Exogenous - bacteria that enter the body.
Fomites - inanimate objects.
Endogenous - bacteria found in the body. Infection-disease caused
by the multiplying of bacteria.
Abscess - walled off inflammation resulting in dead tissue.
Inflammation - swelling that is due to puss and fluids surrounded
by a walled off clot.
Puss - white blood cells.
Subcutaneous - below the skin.
Toxigenic - bacteria that produce toxin.
Toxin - poison
Intoxication - illness that results from ingesting preformed toxins
Agar - nutrient media that allows organisms to grow on it but does
not break down due to the organism's metabolic processes.
Flame the loop - heating an inoculating loop to kill
any bacteria present on it.
Heat fixing a slide - heating a microscope slide
to make bacteria stick to the slide.
Gram stain - procedure used to stain bacteria so that they
can be seen under a microscope.
Gram positive bacteria - bacteria that stain blue.
Gram negative bacteria - bacteria that stain pink.
This is an introductory lesson so the video provides the starting
point for the discussion. One needs to have all of the lab materials purchased
and ready to for use.
To give a specific responsibility while viewing tell the students,
"As you watch the video it is your responsibility to distinguish between
viruses and bacteria, determine the shapes of the viruses and bacteria,
two methods by which bacteria make you sick, three methods of prevention,
and the basic method of growing a bacterial culture."
Note to the teacher: The video is elementary based but has many good
concepts that can be expanded on to make this a useful high school level
START the video where Levar Burton looks up from the microscope after
looking at the amoeba, hydra, rotifer, and water bear. He says, "There
are millions of invisible creatures living in our world."
PAUSE the video where Levar asks, "What do you think a germ
is?" Ask the students to listen to what the six children's definition
of a germ is and have them compare the kids' ideas to their own idea of
what a germ is. RESUME the video.
PAUSE the video after the six children have given their definition
of a germ. Ask the students how many of them honestly agree with the kid's
definition of a germ. Ask the students to give their own definition of a
germ. This will give you a pre-test sort of knowledge as to how much your
students already know. Since this is a high school lesson, warn the students
that the next section is a little story book story about germs. Have fun
with it. Look for the differences between bacteria and viruses. RESUME
PAUSE the video when the narrator says, "Germs are tiny living
beings." Make sure students focus on the term "living" since
this will be an important distinguishing characteristic between bacteria
and viruses. RESUME the video.
PAUSE the video where the narrator says, "the two types of germs
are bacteria and viruses." Tell the students to make two lists of characteristics.
One for bacteria and one for viruses. RESUME the video.
PAUSE the video after the three shapes of bacteria have been presented.
Tell the students it is now time to add some information to the video. The
ball-shaped bacteria is properly called "cocci." The rod-shaped
bacteria is properly called "bacilli." The spiral-shaped bacteria
is properly called "spirilli." When bacteria comes in chains,
it has the prefix "strepto" attached to the shape name. When bacteria
comes in clumps, it has the prefix "staphylo" attached to the
shape. For example, staphylococcus means a clump of round-shaped bacteria.
Streptococcus means a chain of round-shaped bacteria. Bacteria are so small
that the two main defining characteristics of it are its shape (round, rod,
or spiral) and whether it is clumped or chained. RESUME the video.
PAUSE the video after the three shapes of viruses. Ask the students
what the three viral shapes are. Explain to the students that viruses are
simply single or double strands of either DNA or RNA. As a result, they
do not have the characteristics of living organisms. Unlike living organisms,
viruses are not made up of cells. They do not have a nucleus, complex membranes,
organelles, and they contain either DNA or RNA but not both. They do not
move, grow, reproduce, or respire. Therefore, viruses are not living. Bacteria
on the other hand exhibits the characteristics of life and therefore, bacteria
are living organisms. Emphasize that bacteria and viruses are distinct entities
and are not interchangeable terms. RESUME the video.
PAUSE the video after the narrator says that germs are kept out of
the body by the skin and nose hair. Tell the students that bacteria are
also kept out of the body by the mucus in the nose. Damage to the skin,
nose hair, mucus or an excess of bacteria in the environment can allow bacteria
to enter the body. RESUME the video.
PAUSE the video after the scraped knee (from a bicycle accident)
scene. Have the students review methods by which bacteria entered the body.
The video shows sneezing, a shared straw, and skin breakage. Have the students
determine where the bacteria lived in order to be passed from person to
person in these ways. Bacteria live in the nose, mouth, and on the skin
as part of the normal flora of the body. They only cause problems when they
are present in excess or in deficient amounts. In the cases presented, the
bacteria are in excess.
The following information should be added about bacterial habitat and transmission.
The lab activity that goes with this lesson deals with growing Staphylococcus
bacteria. It is important that students understand some fundamentals.
Staphylococcus aureus is usually a pathogenic (disease causing) bacterium.
Many people carry the bacteria as a normal part of their skin's flora. These
people are known as carriers (individuals who transport the bacteria but
do not get sick from the bacteria). Staphylococcus epidermidis is
usually nonpathogenic (not disease causing) bacterium. This bacteria is
also carried by many people as a normal part of their skin's flora.
Habitat: 1. Skin - humans and animals carriers.
2. 20 -50% of humans carry Staphylococcus in their nose but are not
affected by it. They are carriers.
1. Exogenous (bacteria that enters the body)
A.Moisture droplets that enter traumatized tissues - such as sneezing on
an open wound.
B. Fomites (inanimate objects) that touch traumatized tissue - toilet seats,
door handles. Staphylococcus aureus is particularly resistant. It
can live between 6-14 weeks in dried body fluids.
C. Contaminated food - raw milk. A cow with mastitis (swelling of the udder)
passes the bacteria to humans who then get a Staphylococcus infection (not
mastitis). Mastitis is the number one economically detrimental agricultural
disease in the US. Mastitis results in agricultural losses of $2 billion
a year. Note, pasteurization kills Staphylococcus.
D. Staphylococcus food poisoning
2. Endogenous (bacteria found in the body flora of carriers)
A. Compound fractures (bone is exposed through the skin) where the bone
comes in contact with bacteria already in the body.
B. Lowered host resistance - this allows bacteria to increase their growth
rate. AIDS is a good example of lowered host resistance. The body's lowered
immune response allows rapid bacterial reproduction.
C. Excessive antibiotic therapy - changes the makeup of the body's flora
and thus changes the field of competition. As a result certain bacteria
grow rapidly. Example: penicillin halts the growth of most bacteria; however,
it does not halt the growth of Staphylococcus. Staphylococcus has become
resistant to penicillin. Without competition from other bacteria; more room,
food, and etc. are available for the Staphylococcus. As a result, Staphylococcus
reproduction is unchecked.
RESUME the video.
STOP, but do not rewind the video after the statement "germs
make you sick by multiplying or giving off poisons." The following
information should be added about Staphylococcus induced diseases. The main
terms are the same for all bacteria induced diseases, but since the lab
focuses on Staphylococcus so do the given example diseases.
Staphylococcus aureus induced diseases:
Nontoxigenic inflammatory infections Toxigenic infections Intoxication (not
I. Nontoxigenic inflammatory infections: The
main characteristic of the nontoxigenic inflammatory infection is the presence
of abscesses. An abscess is a walled off inflammation resulting in dead
tissue. Inflammation is a swelling that is due to puss (white blood cells)
and fluids surrounded by a wall of clot.
A. Infection/inflammation of the skin and subcutaneous (below the skin)
1. Trauma that results in skin breakage such as being hit with a hammer
can result in a Staphylococcus infection. People who get Staphylococcus
infections in this manner are often nasal carriers of Staphylococcus.
2. Furuncle (boils) are the most common type of nontoxigenic inflammatory
infections. A boil is a superficial infection of hair follicles or sweat
3 Sty is an infection at the base of the eyelash.
4. Carbuncle is a really bad group of boils.
5. Impetigo is where areas of the skin are covered in crusty lesions (infected
areas). This is usually a disease that affects children. The lesions are
not walled off in an abscess. It is highly communicable.
B. Infection/inflammation of the respiratory tract:
1. Tracheobronchitis is a respiratory Staphylococcus infection of the bronchia
or trachea. The bacteria grow and cause inflammation of the bronchial tubes
2. Pneumonia is a lower respiratory Staphylococcus infection of the lungs.
The bacteria grow and cause an inflammation in the lungs.
C. Infection/inflammation of tissues due to bacteria carried by the blood:
1. Endocarditis is an inflammation of the heart tissue (usually the valves)
due to bacterial growth there. The bacteria carried by the blood lodges
on the valves of the heart causing an abscess. As a result, the body tries
to fight off the infection. If the body is successful, no problem. However,
if the body is unsuccessful, the valve tissue dies and so may the infected
person. Having one's teeth pulled is one method of getting this disease.
When the tooth is pulled, an open wound is made in the mouth. This allows
bacteria from the mouth to enter the bloodstream. This is why dentists may
administer antibiotics to patients who have their teeth pulled.
2. Osteomyelitis is an abscess that forms in the metaphyseal region of the
long bones. The abscess on the bone causes the bone tissue to die. The blood
in the metaphyseal region of the bone is not under as great of a pressure
as the blood in the surrounding regions. As a result the bacteria are not
"washed away" thus it is a favorable location for them to grow.
Ninety percent of the cases of osteomyelitis are the result of Staphylococcus
aureus. Many of these cases are the result of Staphylococcus aureus that
was on the skin, entered the bloodstream through a wound, and then settled
and grew in the bone.
II. Toxigenic infections:
Some bacteria produce toxins. Bacterial toxins are poisons that harm the
animal host. There are two types of toxins - endotoxins and exotoxins. Endotoxins
are located in the cell wall of the bacteria. Endotoxins are only active
when released from the cell wall such as when the bacteria dies and degrades.
Exotoxins are toxins that are produced and secreted by the living bacteria.
Staphylococcus produces only exotoxins. The Staphylococcus exotoxin that
is responsible for the most important toxigenic infection symptoms is the
toxic shock syndrome toxin-1 (TSST-1).
In toxigenic infections, the infection is caused by the bacteria, but the
damage to the body is caused by the toxin produced by the bacteria. Since
the toxin is a molecule, it is carried away from the bacteria by the bloodstream.
Therefore, damage to the body occurs away from the sight of infection.
A. Toxic shock syndrome (menstrual and nonmenstrual)
1. Menstrual - occurs in females who use high absorbency tampons. As a result
of toxic shock syndrome, high absorbency tampons are no longer produced
and marketed. Staphylococcus is naturally present in the vagina in small
numbers. When high absorbency tampons are in place, the number of bacteria
increases dramatically, thus increasing the amount of toxin produced. This
results in menstrual toxic shock syndrome. Two possible explanations exist
with the first being the one thought to be the most plausible by researchers.
The vagina is an anaerobic (lacking oxygen) environment. The insertion of
the high absorbency tampon allows air into the vagina, thus it becomes an
aerobic (oxygen present) environment. This allows rapid propagation of the
bacteria. The second explanation is that magnesium ions inhibit Staphylococcus
growth and toxin production. The material in the high absorbency tampons
binds the magnesium ions so that they no longer inhibit bacterial growth.
2. Nonmenstrual - occurs in males and females who have a toxigenic Staphylococcus
infection. Nonmenstrual toxic shock accounts for one third of toxic shock
syndrome cases. The toxin that causes the symptoms is usually TSST-1.
3. How TSST-1 Works: TSST-1 is a superantigen which overstimulates white
blood cells so that they produce an excessive amount of cytokine molecules.
In low concentrations, cytokines are beneficial by helping the immune system
fight off infections; but in high concentrations, they cause the symptoms
of toxic shock syndrome. The symptoms of toxic shock syndrome include:
c. Desquamation (skin peels off)
d. Hypotension - low blood pressure which results in decreased blood flow
to the extremities and thus the person goes into shock. Shock is where the
cardiovascular system shuts down. This is the most important symptom because,
if death is to occur, this is what kills the person.
III. Intoxications (Staphylococcus food poisoning): Intoxications are
illnesses that result from ingesting preformed toxins - usually in food.
Intoxications are not infections since the bacteria do not need to be present
in the body. The toxin only needs to be present for the poisoning to occur.
The toxin responsible for this disease is called staphylococcal enterotoxin.
The toxin stimulates the vagus nerve. The vagus nerve is the abdominal nerve
that is connected to the medulla (part of the brain). The stimulation of
the vagus nerve results in the stimulation of the part of the medulla that
causes vomiting. The person vomits. Staphylococcal enterotoxin is resistant
to heat; therefore, cooking the food does not make it safe for consumption.
Staphylococcus food poisoning results from eating food with the enterotoxin
in it - not the bacteria. Common locations of Staphylococcus in food are
pastry, meat, and any food containing mayonnaise.
Symptoms: One to six hours after the toxin is ingested the body responds
- vomiting and possibly diarrhea. The body usually eliminates itself of
the toxin within 24 hours.
FAST forward the video to the part where the doctor in the story
is looking at the child. PLAY the video.
PAUSE the video after the narrator says, "if a bacteria makes
you sick the doctor may prescribe drugs, but there are no drugs for viral
infections. Shots may be given to prevent viral infections." Ask the
students why this is. (Bacteria are living and thus can be killed by drugs.
Viruses are not living and thus cannot be killed. You cannot kill something
that is not living and remember viruses do not have the properties of living
organisms.) RESUME the video.
PAUSE the video where the narrator says, "you can help yourself
stay healthy by exercising, eating right, and staying clean." Review
this idea with the students. Take special care to note one of the main ways
to avoid bacterial transfer is to wash your hand after using the restroom.
(Bacteria are so small they may not appear to be present but they are.)
RESUME the video.
PAUSE the video where the lab technician calls the red stuff in the
bottom of the petri dish "a dish of food." Discuss with the students
that this growth media is called "agar." Agar is a nutrient media
that allows organisms to grow on it but it does not break down due to the
organisms' metabolic processes. There are different types of agar that allow
different types of bacteria to grow on it. In the lab you will be doing
you will be using Mannitol salt agar. Mannitol salt agar allows Staphylococcus
aureus to grow, but inhibits most other bacterial growth. Tell the students
to pay attention for the lab technician to say, "a dark warm place."
She is referring to an incubator. In the case of the lab you will be doing,
warm is 37 degrees Celsius. RESUME the video.
PAUSE the video after the lab technician says, "beta streptococci."
Ask the students what it should look like. (It is a chain of circles.) Tell
the students to see bacteria they must be stained and looked at under an
oil immersion microscope lens. This special lens allows light to pass directly
into the lens rather than bend where it enters the lens. Bacteria are so
small that every bit of light is needed to see them. The staining procedure
you are going to use in the lab is the Gram Stain. RESUME the video.
PAUSE the video at the picture of E. coli. Ask the students what
shape it is. (The shape is bacilli.) RESUME the video.
PAUSE the video where the lab technician says, "Staph aureus."
Point out to the students that the proper name of the organism is Staphylococcus
aureus. Ask the students what it will look like. (It will be clumps of cocci
bacteria.) Ask the students where this type of bacteria lives. (It lives
on the skin.) FAST FORWARD the video though the moldy food
section and RESUME the video at the section where Levar Burton is
swabbing his mouth. Provide a focus for viewing by telling the students
to watch the procedure carefully. This is the procedure you will follow
in the lab to grow a culture of bacteria.
PAUSE the video after the lab technician puts the loop in the fire
and spreads the bacteria out over the plate. Point out to the students that
the cotton swab was only used to swab the top one-fourth of the agar dish.
The lab technician stuck the inoculating loop into the fire in a procedure
known as "flaming the loop." Ask the students why she did this.
(She did this to kill all bacteria that may be living on the inoculating
loop.) The lab technician then spread the bacteria out very thin. Ask the
students why. (She did this so that individual colonies could grow and be
seen. Otherwise the bacteria are so grouped together no useful information
can be derived.) REWIND the video and show this section over again.
RESUME the video.
STOP the video after the lab technician reviews the idea of keeping
clean. Emphasize to the students it is very important to wash your hands
especially after using the toilet.
After viewing and adding in the discussion topics, you may want
to go back and show parts of the video with the sound turned off. At the
end of the lessons, students will be able to discuss the topic at a higher
level than the video. This is an excellent method of review and reinforcement.
Note to the teacher: It is time to do the lab. The streaking the agar
plates takes about 15 minutes. It is best to do this at the end of a class
period. Incubate the cultures over night and then begin the staining procedure
the following day. Observe the bacteria and do the math exercises the day
Isolation of Staphylococcus aureus lab
Copy and distribute Figure 1 to the students.
1A. Using a new sterile cotton swab, collect specimens from human skin.
1B. To collect samples from dry surfaces, simply rub the swab on the surface.
Sweaty surfaces (such as arm pits) work the best. Areas that are particularly
clean (especially if they have been recently washed with antimicrobial soap)
do not work well. Rub hard enough to get a good sample but do not rub so
hard that you injure the subject. Bacteria are so small you will not see
anything on the swab, but the bacteria is present.
Rub the cotton swab on the collection sight and then run the swab over the
top one-fourth of the Mannitol salt agar petri dish. See Figure 1.
Used swabs need to be decontaminated by either autoclaving them or placing
them in a 10% bleach/water solution. The decontaminated swabs should then
be placed in a separate trash bag and incinerated.
1. Light the Bunsen burner. "Flame the loop" by placing the loop
part of the inoculating loop in the Bunsen burner flame until the loop turns
This kills all bacteria that may be on the loop. Place the loop in a piece
of bacteria-free agar to cool it. "Streak" the Mannitol salt agar
plate. To streak the plate, using the flamed loop smear some of the sample
at about a 90 degree angle from the swabbed area. Streak back and forth
until about one-fourth of the plate is covered. See Figure 1. At a 90 degree
angle from this streaked area, streak another one-fourth of the plate. See
Figure 1. The goal of this is to spread out the sample so that the bacteria
are not touching. Therefore when they grow, they will form isolated colonies.
Reflame the loop so that you leave it clean.
2. Place the streaked agar plates in an incubator at 37 degrees C for 24
1. Bacteria will be visible 24 hours later. The Mannitol salt agar should
have mostly Staphylococcus growing on it. Staphylococcus aureus
ferments the Mannitol and therefore is a yellow color. Staphylococcus
epidermidis does not ferment the mannitol and therefore is red.
Copy and distribute Table 1 to the students.
Look at your plates and determine if fermentation has taken place. Record
your results in table 1.
The next thing you will need to do to confirm you have grown Staphylococcus
is the Gram stain. Staphylococcus are Gram positive cocci in clusters.
Gram positive bacteria stain blue and Gram negative bacteria stain pink.
Perform the Gram stain as follows and record your results in table 1.
The dyes used in this procedure will stain your clothes. Wear appropriate
attire. Wearing latex gloves during the staining part of this procedure
will prevent your hands from turning colors.
2a. Light the Bunsen burner. "Flame the inoculating loop" by placing
the loop in the Bunsen burner flame. This kills all bacteria that may be
on the loop. Place the loop in a piece of bacteria-free agar to cool it
then gently touch the loop to some of the bacteria that has fermented the
Remember this is a yellow color. Get a little on the loop.
2b. Put a drop of water on a clean slide. Smear the bacteria into the water
and spread it around until it is evenly distributed.
2c. "Heat fix" the slide. This process attaches the bacteria to
the slide. Hold the slide with your fingers and pass it back and forth through
the Bunsen burner flame until the slide is completely dry. It should never
get hotter than what you can comfortably hold. If it does you have cooked
the bacteria and they can't be seen. Heat fix the slide until it is dry.
2d. Hold the slide on an angle over the sink and drop several drops of crystal
violet on the bacteria. Allow this to set for one minute.
2e. Run enough tap water over the slide to wash the crystal violet off.
Do not scrub.
2f. Hold the slide on an angle over the sink and drop several drops of Gram's
iodine on the bacteria. Allow this to set for one minute.
2g. Run enough tap water over the slide to wash the Gram's iodine off. Do
2h. Hold the slide on an angle over the sink and drop no more than five
drops of Gram decolorizer (isopropyl alcohol works) on the bacteria. Go
to step 2i immediately or all the stain will be removed - you will have
messed up. All of your bacteria will be pink.
2i. Run enough tap water over the slide to wash the Gram decolorizer off.
Do not scrub.
2j. Hold the slide on an angle over the sink and drop several drops of Safranin
O on the bacteria. Do not scrub.
2k. Run enough tap water over the slide to get the excess Safranin O off.
Do not scrub.
2l. Blot the slide dry with a clean paper towel.
2m.Place a drop of immersion oil on the bacteria and place the slide under
the oil immersion lens of the microscope.
2n. Focus. If you have little blue dots in clumps, you are looking at Staphylococcus
Health professionals determine the amount of bacteria in your body by using
a procedure similar to the one you used in table 1. How much bacteria in
this case Staphylococcus aureus is in your body? This exercise is at best
a guess. Count the number of bacteria on the slide. Measure the length and
the width of the slide. Multiply length times width. This gives you the
surface area of the slide. Write this number down with the number of bacteria
present. Measure how tall you are and call this number "h." Measure
one-half of your body width and call this number "r." Plug these
numbers into the formula for calculating the surface area of a cylinder.
The formula is (2)(")(r)(h) + (2)(")(r2) = your surface area.
Take this number and divide by the surface area of the slide. Finally multiply
this number times the number of the bacteria on the slide. The number should
be huge (billions, trillions or greater). This gives you an approximation
of how many Staphylococcus aureus bacteria are on your skin. Make sure all
of your measuring units are the same.
2o. Clean up. Wash the slides and your hands with an antimicrobial soap.
DISPOSAL -- Used petri dishes need to be decontaminated by either
autoclaving them or placing them in a 10% bleach/water solution. The decontaminated
petri dishes should then be placed in a separate trash bag and incinerated.
Make a raw data table on the chalk board. Have each class member fill in
how many Staphylococcus bacteria are present on their skin. Upon completion
of the raw data table, have the students calculate the mean number of bacteria
present. Use of scientific notation will be a benefit. Finally have the
students graph the data. Discuss what the graphs look like and interpret
Have students contact health officials (doctors, dentists, hospitals,
clinics, etc.) and find out which bacterial infections occur most often.
This data should be presented to the class orally supported by a graph of
the raw data. If computers are available, all graphs should be computer
generated. Students should draw some conclusions about the frequency and
location of bacterial infections.
Have a doctor or other health professional come to the school as a guest
speaker. Have the speaker discuss growing bacterial cultures and interpreting
the results. Have the speaker discuss how a method for treatment is determined.
Via the Internet, have students send messages all over the world to health
organizations to determine the prevalent bacterial infections and method
of treatment. Students should determine if certain infections are more prevalent
in rural, urban, developed, or third world areas. Data should be presented
orally to the class and include computer generated graphs.
Future topics of discussion and lab activities include:
VIDEO AVAILABLE FROM
- The body's natural defense system (antibodies, white blood cells,
- Antibiotics, antimicrobial agents, and vaccines.
- Using the bacteria you have already grown on the Mannitol salt agar,
you can grow pure cultures of Staphylococcus aureus in brain/heart infusion
broth. Using a flamed and cooled inoculating loop, place a colony of Staphylococcus
aureus in the broth and incubate it for twenty- four hours at thirty-seven
degrees Celsius. This culture can then be swabbed onto the entire surface
of a 100 millimeter Mueller-Hinton plain agar plate. Place one Difco Dispens-O-Disc
Susceptibility Test Disc of ampicillin 10 mcg, erythromycin 15 mcg, penicillin
G 10 units, and tetracycline 30 mcg on the agar. Incubate the culture for
twenty-four hours at thirty-seven degrees Celsius. Measure the zones where
no bacteria grew and compare it to the chart that comes with the susceptibility
test discs. Use this information to determine which antibiotic is most effective
at killing Staphylococcus aureus. One set of test discs is enough for a
class of twenty-five.
- Taping it off of the air. See your local PBS schedule.
- Idaho State Library.
- Reading Rainbow programs or teacher guides-contact GPN 1-800-228-
Lesson developed by Master Teacher John Lindley, Marsing High
Technical microbiological assistance provided by Dr. Greg Bohach, Department
of Microbiology, University of Idaho, Moscow, Idaho. Mathematical assistance
provided by Jody Hoff, Homedale High School, Homedale, Idaho.
Click here to view the
worksheet associated with this lesson.
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