Most Dangerous Woman in America, The
To test the efficacy of different types of hand hygiene.
- 2 14.5 oz. cans of sliced beets (10-12 slices per can)
- can opener
- 1 pair new plastic gloves
- plastic forceps or tongs
- isopropyl alcohol (for disinfecting)
- copy of the "Which Wash Wins?" student handout
- copy of the "Hand-Washing Methods" student handout
- 3 100 mm x 15 mm sterile plastic Petri dishes
- cotton swabs
- permanent marker
- access to sink with water (Teams 1, 2, and 3 only)
- regular soap (Team 2 only)
- antibacterial soap (with antiseptic like triclosan) (Team 3 only)
- hand sanitizer (with ethyl or isopropyl alcohol) (Team 4 only)
- paper towels (Teams 1, 2, and 3 only)
Mary Mallon was a healthy carrier of the typhoid bacteria. Because she was a
cook and handled food, she transmitted the disease to some of the people she
worked for. Hand washing is one way to help stem the transmission of disease.
In this activity students will test the efficacy of different types of hand
Prior to the activity, thoroughly disinfect the tongs by spraying or soaking
them in alcohol (you may want to wash the can opener and tongs in a dishwasher
and store them in a plastic bag prior to disinfecting). (Note: To increase the
sterility of the experiment, consider using sterile agar plates instead of the
Ask students if they have ever seen a sign in a restaurant bathroom that
read: "Employees must wash hands." Why do students think these signs are
Ask students what they think would be the best way to keep hands clean. What
kinds of products, if any, do they think would be best? What water temperature?
What amount of time spent washing? Write students' answers on the board.
Tell students that they are going to test four methods a fifth group will
serve as the control of hand hygiene (you may want to adapt these methods to
reflect students' suggestions): 1) water only, 2) regular soap, 3)
antibacterial soap, and 4) hand sanitizer.
Organize students into five teams of four students each and provide each
team with a set of materials. Each team will be assigned one of the following
Control Team: no washing method
Experimental Team 1: washing with water only
Experimental Team 2: washing with regular soap and water
Experimental Team 3: washing with antibacterial soap and water
Experimental Team 4: washing with hand sanitizer only
Have each team develop a hypothesis of which of the four methods it thinks
will work best and why. Then have students conduct the experiment as outlined
in their handouts. As students start their hand-washing techniques, put on the
plastic gloves and open the two cans of beets. Have each team use the tongs to
retrieve three beet slices, one for each of the team's three Petri dishes. You
may want to disinfect the tongs with alcohol between team uses.
Have students record the results in a journal each day, making sure to
include diagrams. After four days, compare the growth on the beets from the
different teams. As a class, answer the following questions:
How did each set of beets compare to the control team's beets?
Which experimental team's beets had the least bacteria?
What areas (palms, in between fingers, under nails) were washed
the most thoroughly by each technique? What areas were washed the least thoroughly?
Was there any growth on the control beets?
Discuss the results with students. What results were most surprising? It's
likely that all the beets showed some microbial growth because the experiment
was not completely sterile. Discuss with students where microorganisms might
have come from (beet, plastic tongs, cotton swab, Petri dish, tap water, air).
How could the experiment have been made more sterile?
To conclude, discuss with students why and when it is appropriate to wash
As an extension, have students research the controversy about whether using
antibacterial soaps encourages the growth of new bacteria that are resistant to
beets used in this experiment should just contain normal molds and bacteria.
The beet slices can remain in their Petri dishes and be disposed of in the
regular trash. Spray with a disinfectant, such as Clorox, prior to disposing.
Make sure students do not touch the beets after sealing their Petri dishes.
may want to review the following terms with students:
bacteria: microscopic, single- celled organisms that can be helpful or
harmful to the human body
contagious: able to be transmitted to others, through direct or indirect
epidemiology: branch of medicine that studies the causes, distribution,
and control of diseases in populations
infectious: capable of causing an infection
quarantine: enforced isolation or restriction of a person or persons to
slow or halt the spread of a contagious disease
An individual can have an infection yet not be contagious. For more information
on contagious diseases, including incubation and contagious periods for
specific diseases, see www.childrenshospitaloakland.org/health_library/pa/hhg/incubate.htm
Molds and some kinds of bacteria are most likely to grow on the beets. The
molds will probably look fuzzy green or white while the bacteria may be one of
several colors (such as pink, yellow, or brown) or colorless and look shiny or
dull. The bacteria are likely to grow in lawns (individual colonies that merge
together to form a mat of bacteria). The beet provides the nutrients and water
the bacteria and molds need to grow.
The growth on the beets provides evidence that microorganisms can be
transmitted by hands. One strength of that evidence is that all of the control
beets likely showed growth while the beets for the teams that used
antibacterial soap and hand sanitizer likely showed less growth. One weakness
is that the experiment was not entirely sterile; bacteria and mold from several
sources could have contaminated the beets.
According to the Centers for Disease Control (CDC), plain soap is good at
reducing bacterial counts, antibacterial soap is better, and an alcohol-based
handrub is the best. However, students' results may vary depending on how well
they washed their hands with each type of cleaner. You may want to repeat the
experiment with students and have them wash their hands for a full minute and
compare results of both trials.
Remind students that while their hands contain many harmless bacteria, they can
also transmit bacteria and viruses that can cause illness. According to the
Centers for Disease Control, one of the most important steps individuals can
take to keep from getting sick is to wash their hands.
Both alcohol-based sanitizers and antibacterial soaps can kill harmful
bacteria, such as streptococcus, salmonella, and E. coli, but do not claim to
kill viruses (although some viruses are susceptible to these cleansers).
Sanitizers work by using alcohol to kill the bacteria (they usually contain
60% to 95% ethanol or isopropanol). Antibacterial soaps rely on an antiseptic
agent, such as triclosan, to kill the bacteria. Regular soap, which can remove
bacteria through the action of its bubbles, is not designed to kill bacteria or
Hands should be washed at the following times: before, during, and after
preparing food; before eating; after using the bathroom; after exposure to
animals or animal waste; after handling garbage; after coughing, sneezing, or
blowing your nose; and if you are sick or have been around a sick person.
Because bacteria can be transmitted to food, it is especially important that
people involved with food preparation (as Mary Mallon was) frequently and
properly wash their hands so they do not spread disease by fecal-oral
transmission. For a full list of when food employees are supposed to wash,
NOVA Web Site—The Most Dangerous Woman in America
Find articles, interviews, interactive activities, and resources in this
companion Web site to the program.
The Living City
Reviews in time line format the life, health, and urban transformation of New
York City during the decades between the end of the Civil War and the end of
World War I.
Stalking the Mysterious Microbe
Provides background information on microbes and experiments.
Reviews the story of Mary Mallon and provides links to additional information
about typhoid fever.
What Should Be Done About Mary Mallon
Includes discussion questions related to Mary Mallon's case and provides access
to related primary source documents.
Baker, S. Josephine.
Fighting for Life.
New York, Arno Press,1974 [c1939 ].
Provides an autobiographical look at the life and work of S. Josephine Baker,
one of the first public health officers who approached Mary Mallon.
Typhoid Mary: An Urban Historical.
New York: Bloomsbury Publishing,2003.
Reveals the context in which Mary Mallon lived and the obstacles she faced as
an Irish woman immigrant.
Diner, Hasia R.
Erin's Daughters in America: Irish Immigrant Women in the Nineteenth Century.
Baltimore: Johns Hopkins University Press, 1983.
Portrays the story of a group of Irish immigrant women who overcome barriers of
poverty, ignorance, and disease to succeed in America.
Hammonds, Evelynn Maxine.
Childhood's Deadly Scourge: The Campaign to Control Diphtheria in New York City,1880-1930.
Baltimore: Johns Hopkins University Press,1999.
Explains how New York City became the first U.S. city to apply laboratory-based
advances in bacteriology and immunology to the treatment and prevention of
Kraut, Alan M.
Silent Travelers: Germs, Genes, and the "Immigrant Menace."
New York: Basic Books,1994.
Covers immigration and health from a historical perspective, and includes
accounts of how immigration and public health policies have influenced each
other in the American experience.
Walzer Leavitt, Judith.
Typhoid Mary: Captive to the Public's Health.
Boston: Beacon Press,1996.
Explains the science of germ theory and explores the conflicting perspectives
of the players in Mary Mallon's story, including journalists, public health
officials, the law, and Mary herself. NOVA's "The Most Dangerous Woman in
America" was based on this book.
The "Which Wash Wins?" activity aligns with the following
National Science Education Standards:
Science Standard F:
Science in Personal and Social Perspectives
Risks and benefits:
Individuals can use a systematic approach to thinking critically about
risks and benefits. Examples include applying probability estimates to risks
and comparing them to estimated personal and social benefits.
Important personal and social decisions are made based on perceptions of
benefits and risks.
Science Standard F:
Science in Personal and Social Perspectives
Personal and community health:
The severity of disease symptoms is dependent on many factors, such as
human resistance and the virulence of the disease-producing organism. Many
diseases can be prevented, controlled, or cured. Some diseases, such as cancer,
result from specific body dysfunctions and cannot be transmitted.
Classroom Activity Author
Developed by WGBH Educational Outreach staff.