Hypothesis

The Five-Second Rule – Is It True?

Llew Falla, Grade 7

St. Anne School

Abstract

Food poisoning is an illness caused by eating food contaminated by disease-causing bacteria, viruses, or fungi, also called pathogens. The effects of food poisoning develop within several hours or up to two days after eating contaminated food. Symptoms usually include nausea, abdominal and stomach cramps, vomiting, and diarrhea. More than 80 million people in North America suffer from food poisoning each year and as many as 9,000 die from its effects. A survey of students at St. Anne Elementary School showed a belief in the Five-Second Rule. This urban legend states that “if a piece of food falls on the ground then it will not contract germs (pathogens) if picked up within five seconds”. In this study, experiments were done to test this hypothesis. Nutrient rich agar contact plates were placed on surfaces around the school and then incubated in an oven. It was seen that the Five-Second Rule was not true. Unlike baseball, if the food hits the ground – it’s out!

Purpose

The purpose of this experiment was to determine if bacteria would transfer to nutrient rich agar contact plates by placing them on common school surfaces. Experiments were also done to determine if different surfaces in the school transferred different amounts of bacteria.

Hypothesis

If a piece of food falls on the ground then it will not contract pathogens if picked up within five seconds.

Introduction

A survey of students at St. Anne Catholic School showed that all of the children surveyed in Grades 4, 7, and 8 had heard of the rule. The survery also found a difference between boys and girls. 47% of the girls believed that food was still safe to eat after contact with the floor as compared to 84% of the boys. No difference was observed between the grades. This urban legend states that “if a piece of food falls on the ground then it will not contract germs (pathogens) if picked up within five seconds”. In this study, experiments were done to test this hypothesis.

Materials

· 40 agar-filled contact plates for total bacteria(from Boreal)

· stop watch

· coloured markers

· laboratory convection oven capable of maintaining 37 °C.

· magnifying glass with built in light

Procedure

1. Locations to be tested were identified.

2. Plates were opened and placed on surfaces for 1, 3, 5, 7 and 10 seconds.

3. Each plate was marked according to its location and time that the plate contacted the surface.

4. One plate was opened and exposed to the air for each of the specified times (control).

5. One plate was not opened as a control.

6. All plates were incubated in a convection oven at 37°C for 24 hr.

7. The number of bacteria colonies and surface area covered by bacterial growth were recorded.

Variables

· Independent Variables: testing locations, exposure time on surfaces

· Dependent Variable: number of bacterial colonies, surface area covered by bacterial growth

· Control Variables: incubation time, incubation temperature, testing procedure

Observations

Discussion

In this experiment, agar-filled contact plates for total bacteria were used to test the hypothesis. These plates were chosen because bacteria are simple life forms that do not have a nucleus, grow quickly in nutrient rich environments, and are the most common pathogens of dropped food.

The three variables that were needed to perform this study are the independent variables, dependent variables and control variables. Independent variables are those conditions that were controlled by the experimenter, such as the testing locations and the exposure time on the surfaces. The dependent variables are measured to indicate a change as the independent variables are controlled. The number of bacterial colonies and surface area covered by bacterial growth are the dependent variables. Three control variables, namely, incubation time, incubation temperature and testing procedure are all the factors that are kept constant.

Seven locations around the school were randomly chosen for testing. They were, as follows: computer keyboard, principal’s desk, toilet seat, kitchen counter, lunch bag, floor near garbage pail, student desk, and a student’s desk. The plates were allowed to contact the surface for 1, 3, 5, 7 and 10 seconds (using a different spot each time). A control was run for each of the times by opening the plate, exposing the agar to the air for 1, 3, 5, 7 and 10 seconds. One plate remained closed.

The plates were placed in a convection oven for 24 hours at 37° C and then checked for bacteria growth by examining the plates using a magnifying glass. The number of bacteria colonies and the surface area covered were recorded.

All of the plates tested showed that bacteria transferred from the testing site to the contact plate. The most growth was seen with plates from the floor near the garbage can. All of the testing times showed significant bacterial growth. The surface with the least amount of bacterial growth was the keyboard. This was unexpected and may be due to the shape of the keys. Only the tops of the keys touched the plate because of the concave shape of the keys. The surprising results came for the lunch bag. Significant bacteria growth was seen from all 5 testing times.

None of the control samples showed any bacteria growth except for the 3 second sample which had one small colony. This colony may have come from the air when the plate was opened.

Conclusions

Bacteria were found to transfer from all of the tested surfaces to the contact plates in as little as one second. Therefore, the five second rule was found not to be true.

Applications

Food poisoning is very common with more than 81 million people in North America suffering from its effects each year. This study showed how easily food can be contaminated by bacteria. If food drops on the ground, throw it out.

Errors

1. There was a variation in the location of specific spots tested. For example, five tests were done around the floor of the garbage can area. It is likely that one spot may contain more bacteria that another spot in the same area.

2. The parabolic shape of the keys on the keyboard did not allow the plate to make full contact with the keys.

3. Only bacteria grew on the contact plates; no other pathogens were cultured.

Future Work

1. Only moist contact plates were used in this experiment. Another study should be done to determine if bacteria grow differently on a dry versus moist food environment.

2. Many types of bacteria are harmless to humans. The type of bacteria that grew on the contact plates could be investigated to determine if any were harmful.

Acknowledgements

Mr. Gelinas, Principal, St. Anne School

Mr. McHenry, Teacher, St. Anne School

Mrs. Megan Sygrove, Office Professional, Dow Chemical

Dr. Johna Rajan, Microbiologist, Dow Chemical

Ms. Theresa Warren, Health Inspector Lambton Community Health Services

Bibliography

Encarta, 2001 CD-ROM

http://www.rgj.com/news/stories/html/2003/10/06/53393.php

http://en.wikipedia.org/wiki/Five_second_rule

http://www.innvista.com/HEALTH/MICROBES/bacteria/foodcont.htm

http://msucares.com/health/food_safety/foodfaq6.html

http://www.innvista.com/HEALTH/MICROBES/patho.htm

http://www.waff.com/Global/story.asp?S=1483067

http://www.colostate.edu/orgs/safefood/NEWSLTR/v8n3s03.html

http://digestive.niddk.nih.gov/ddiseases/pubs/bacteria/

http://aggie-horticulture.tamu.edu/extension/poison.html
http://www.schoolscience.co.uk/content/4/biology/sgm/sgmbugs3.html

http://www.coscosci.com/sci-exper/petridishes.htm

http://www.sciencekit.com/category.asp_Q_c_E_433415

Vecchione, G. (1998) Make-It-Yourself Science Fair Projects, New York: Scholastic

Bochinski, J.B. (1991) The Complete Handbook of Science Fair Projects, New York, Wiley

Appendix

Common Foodborne Diseases Caused by Bacteria

Bacteria Responsible	Description	Habitat	Types of Foods	Symptoms	Cause	Temperature Sensitivity
Staphylococcus aureus	Produces a heat-stable toxin	Nose and throat of 30 to 50% of healthy population;	Meat and seafood salads, sandwich spreads	Nausea, vomiting and diarrhea within 4 to 6 hours. No fever.	Poor personal hygiene	No growth below 4^o C. Bacteria are destroyed by normal cooking but toxin is heat-stable.
Salmonella	Produces an intestinal infection	Intestinal tracts of animals and man	High protein foods – meat, poultry, fish and eggs.	Diarrhea nausea, chills, vomiting and fever within 12 to 24 hours.	Contamination of ready-to-eat foods, insufficient cooking and recontamination of cooked foods.	No growth below 4^o C. Bacteria are destroyed by normal cooking.
Clostridium botulinum	Produces a spore and requires a low oxygen atmosphere.	Soils, plants, marine sediments and fish.	Home-canned foods.	Blurred vision, respiratory distress and possible DEATH.	Improper methods of home-processing foods.	Type E and Type B can grow at 3^o C. Bacteria destroyed by cooking
Listeria monocytogenes	Survives adverse conditions for long time periods.	Soil, vegetation and water. Can survive for long periods in soil and plant materials.	Milk, soft cheeses, vegetables fertilized with manure.	Mimics meningitis.	Contaminated raw products.	Grows at refrigeration temperatures. May survive minimum pasturization tempertures (72^o C. for 15 seconds.)
Campylobacter jejuni	Oxygen sensitive, does not grow below 30^o C	Animal reservoirs and foods of animal origin.	Meat, poulty, milk, and mushrooms.	Diarrhea, abdominal cramps and nausea.	Improper pasteurization or cooking. cross-contamination.	Sensitive to drying or freezing. Survives in milk and water at 3^oC for several weeks.
Enteropathogenic E. coli	Can produce toxins that are heat stable and others that are heat-sensitive.	Feces of infected humans.	Meat and cheeses.	Diarrhea, abdominal cramps, no fever.	Inadequate cooking. Recontamination of cooked product.	Organisms can be controlled by heating. Can grow at refrigeration temperatures.

Common Food Borne Diseases Caused by Viruses

Disease	Incubation Period	Principal Symptoms	Types of Foods	Mode of Contamination	Prevention of Disease
Hepatitis A	15-50 days	Fever, weakness, discomfort; often jaundice	Raw or undercooked shellfish, sandwiches, salads, etc.	Human fecal contamination, via water or direct	Cook shellfish thoroughly, general sanitation
Norwalk-Like Viruse	1-2 days	Nausea, vomiting, diarrhea, pains, headache, mild fever	Raw or undercooked shellfish, sandwiches, salads, etc.	Human fecal contamination, via water or direct	Cook shellfish thoroughly, general sanitation
Rotaviruses	1-3 days	Diarrhea, especially in infants and young children	Raw or mishandled foods	Probably human fecal contamination	General sanitation

Common Food Borne Diseases Caused by Fungi

Disease	Incubation Period	Principal Symptoms	Types of Foods	Mode of Contamination	Prevention of Disease
Aspergillus flavus	Varies with dose	Vomiting abdominal pain liver damage: liver cancer	Grains, peanuts, milk	Molds grows on grains and peanuts in field or storage; cows fed moldy grain	Prevent mold growth; don’t use moldy grain
Fusarium	1-3 days	Diarrhea, nausea, vomiting; destruction of skin and bone marrow; sometimes death	Grains	Mold grows on grains if left in field during winter	Harvest grain in fall; don’t use moldy grain
Ergotism	Varies with dose	Gangrene (limbs die and drop off); or convulsions and dementia	Rye, wheat, barley, and oats	Fungus grows on grain in field	Remove sclerotic from harvested grain