Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Add three disposable droppers full of NaOH solution to 200 mL of tap water in one selected Styrofoam^® “food” bowl and stir.
2. Add 200 mL of tap water to 14 other bowls and place a food card in front of each. The food category card (e.g., Breads, Drinks) should be placed between or above the bowls.
3. Place one plastic spoon inside each bowl and then spread out the bowls along a counter or around a table.

Safety Precautions

Although materials in this activity are considered non-hazardous, none of the solutions should be consumed. Wear chemical splash goggles and follow all normal lab safety procedures. Wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All solutions used in this lab can be disposed of down the drain with plenty of water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 individual students. This laboratory activity can reasonably be completed in one 50-minute class period. The Prelab Activity, including answering the questions, should be done the day before the lab. Data analysis and calculations may be completed the day after the lab.
• To preserve the food cards for long term use, you may want to laminate them first before cutting them out.
• Any color of pink, regardless of how light-colored it is, means a person is sick. Holding a sheet of white paper behind the cup will help detect slight color changes.

Teacher Tips

• To enhance the drama of the Prelab Activity, you may want to find and play the opening music to the old Dragnet television series.

• The task of determining which food was most responsible for making people sick could be made a little more challenging by adding one dropper full of NaOH to another “food” item.
• This activity works best with 15–30 people. A group smaller than 15 makes data analysis difficult whereas, a group much larger than 30 makes data collection difficult.
• Show students the importance of memory and recall when trying to solve food poisoning cases by laminating the cards and writing a price for each “food” on the card with a washable marker. As each food is chosen and “put on the plate,” have students mentally add up the cost of the entire meal. When they return to their seats, have them write the total cost of the meal above the data table before they begin writing down the food items they selected in the data table.

Answers to Prelab Questions

1. Based on the information given by Mr. and Mrs. Gurr, which bacterium was the probable cause of Mr. Gurr’s illness? Explain the specific reason(s) for your choice. (Hint: Review the Background information.)

Salmonella, because symptoms occur within 12–72 hours after ingestion, with vomiting, diarrhea, stomach cramps, fever and/or chills as characteristic symptoms. Also, the Background information indicates that Salmonella bacteria are found in egg yolks, which would be found in an egg salad sandwich.

2. Which of the food(s) that Mr. Gurr ate may have been contaminated? Give one reason for your choice.

It was not the Coke^® because it is too sweet and too cold. It could have been either the egg salad sandwich or the green salad, prepared with unwashed hands and neither one refrigerated.

3. Why didn’t Mrs. Gurr get sick?

She didn’t eat the same food as Mr. Gurr.

4. As an employee of the County Health Department, you are required to ensure that food purchased from any eating establishment is safe. What would you recommend that the owners of Sam ’n’ Ella’s Café do to prevent anyone else from getting sick?

Refrigerate food below 40 °F or keep food hot above 140 °F. Wash hands before handling food and especially after using the restroom.

Sample Data

Answers to Questions

1. Based on the calculation of Relative Risk (Column H), which food(s) items were contaminated? Explain the reason for your answer.

Whichever “food item” was contaminated by the instructor prior to the lab will determine student answers.

2. If only the “raw” numbers found in Columns B, C, E and F were added together—Total Number Sick versus Total Number Healthy—to determine which food item(s) was/were contaminated, would the answer to Question 1 have been as certain? Explain your answer using data from Table 1.

No, because the total in each category (sick vs. healthy) only differed, in many cases, by a few numbers. For example, the number of people who got sick in the veggies/dip row were 14 compared to 16 who did not get sick.

3. 1. Was this experiment a controlled experiment? Explain your answer.

      Yes, because there were two separate groups involved, one group that ate specific kinds of food and one group that did not.

   2. Which group was the experimental group?

      The people that ate the food that made them sick.

   3. Was there a control group? If yes, which group was it?

      Yes, the group that did not eat the food that made other people sick.

   4. How was the control group selected?

      The control group was chosen randomly and included all those who chose not to eat the food that made other people sick.

4. Based solely on elapsed time from ingestion to illness (because you don’t know the symptoms of each of the “class victims”), which bacteria type(s) may have been responsible for people in your class getting “sick”? Support your answer using information from the Background section.

The bacterium that most likely made the people in the class “sick” was Staphylococcus aureus. The food poisoning symptoms for this bacterium occur within 2–8 hours.

5. As a medical detective, what do you suspect was the likely source of the bacteria that caused people to get sick? Support your answer using information from the Background section.

Whichever “food item” was contaminated by the instructor prior to the lab will determine student answers. In our example, potato salad can easily become contaminated simply by leaving it unrefrigerated for several hours.

Introduction

In spite of many technological advancements as well as increased food handling regulations and oversight, the Center for Disease Control (CDC) in Atlanta, GA, estimates that in the United States, about 76 million people get sick from eating contaminated food each year. For more than 300,000 people, the symptoms are severe enough to put them in the hospital, and of those about 5,000 people die! What causes a food poisoning outbreak? What can be done to bring it under control?

Concepts

• Disease transmission

• Problem-solving
• Food safety
• Data collection and analysis

Background

When food poisoning cases are reported, a medical “detective” is assigned to find out how the individuals got sick. Once the cause has been determined, it becomes easier to choose the steps necessary to correct the conditions that led to the poisoning. There are several types of bacteria known to cause food poisoning. Among them are: C. jejuni, E. coli O157:H7, Shigella, Staphylococcus aureus, Salmonella and C. botulinum. Food poisoning occurs because bacteria in food produce toxins (poisons) whose effects vary depending on the individual and the amount of toxin ingested.

Closteridium jejuni is the leading cause of bacterial diarrhea in the USA. Children under 5 and young adults are the most susceptible. This bacterium is common in the intestines of many animals—cats, dogs, birds, chickens and flies. The symptoms—fever, abdominal pain, nausea, headache, muscle pain and diarrhea—begin 2–5 days after ingestion and may last up to 10 days; relapses are common.

Shigella and E. coli infections are similar and it may be difficult to determine which organism is responsible for the illness. Shigella and E. coli are the most common causes of the so-called “Montezuma’s Revenge” that travelers to foreign countries may experience. E. coli infections from food come mainly from dairy products and undercooked beef. Symptoms, such as severe abdominal cramps and watery diarrhea, appear within 1–3 days. In uncomplicated cases, the diarrhea lasts from 1–8 days. Shigella toxin infections result in symptoms that begin 36–72 hours after eating and last 2–3 days. Diarrhea, nausea, vomiting, fever and abdominal cramps are common symptoms but in about 40% of infected children—convulsions can occur.

Staphylococci bacteria are everywhere in the environment, including on the surface of human skin. This bacterium is spread mostly by the poor sanitary practices of food handlers. The toxin that is produced is then released into the food. When a person eats food laced with Staphylococci toxin, the bloodstream carries the toxin throughout the body. Within 2–8 hours after eating contaminated food, a person may experience vomiting, diarrhea, and severe abdominal cramps but have no fever. The symptoms may last 3–6 hours but rarely persist for more than 24 hours.

Found primarily in egg yolks, raw or undercooked chicken and other meats, unpasteurized dairy products, fish and shrimp, Salmonella produce an endotoxin, a toxin produced inside cells. These bacteria invade the cells that line the small intestine, resulting in inflammation and reducing the intestine’s ability to absorb nutrients and reabsorb water. The usual clinical symptoms of severe diarrhea, vomiting, abdominal cramps, fever, chills and nausea begin within 12–72 hours after ingestion and may continue for two to five days. Severe cases of dehydration or systemic, blood-borne infections may develop from Salmonella infections.

Closteridium botulinum, the cause of adult and infant botulism, is an anaerobic bacterium that thrives in environments without oxygen. This toxin, most common in factory or home-canned foods, causes the characteristic “bulge” in the lids of unopened cans or bottles. The toxin is classified as a neurotoxin, which affects the nervous system, but without such symptoms as diarrhea and vomiting associated with other bacterial toxins. Symptoms manifest themselves within 12–72 hours and begin with a general weakness and dizziness. These are followed by double vision, paralysis of the eye muscles, and difficulty speaking and swallowing as the paralysis moves down the body. The usual cause of death is by asphyxiation as the diaphragm—the muscle that regulates breathing—becomes paralyzed. Botox, short for Botulinum toxin, is one of the most poisonous natural substances known to man. Only one gram—the mass of a large paperclip—would be sufficient to kill 20 million people. Fortunately, this toxin is very heat-sensitive and it can be made harmless by boiling for 10 minutes.

Knowing the major symptoms caused by each bacterium can help answer the question, “Which bacterium was involved?” The individual(s) who get sick from eating tainted food can assist in solving the mystery if they are able to talk and answer a series of important questions, such as:

• What did you eat during the 24 hours prior to becoming ill?
• Did you notice anything unusual about the food prior to or while eating it?
• Where did you eat?
• How long after eating did you become ill?
• Did you have a fever?
• Did you develop chills?

Using the answers to these questions, the “detective” may be able to uncover the cause of the illness and which food was contaminated. Since bacteria are in and on all food, one of the best ways to prevent food poisoning is to keep food at temperatures below 40 °F or above 140 °F. Adhering to these temperature guidelines prevents bacteria populations from growing too large and producing sufficient toxin to make people sick.

Experiment Overview

The purpose of this activity is to graphically demonstrate how quickly food-borne pathogens can affect people. The results will illustrate the importance of both rapid and accurate data collection to locate the source(s) of the outbreak as quickly as possible.

Materials

Prelab Questions

Activity

Follow along as members of the class read the various parts of the role play drama. Then answer the questions at the end.

NARRATOR: Ladies and gentlemen, the story you are about to hear is not true but was written to illustrate the importance of food safety.

JOE FRIDAY: The city: Chicago, windy Illinois metropolis on the western shore of Lake Michigan and home to Blackhawks, White Sox, Bears and Cubs. My job: To sniff out eating establishments which violate the city’s food-handling safety code. I work for the County Health Department. My name’s Friday. My partner’s name is Setter Day. We were filling in for the 911 operator on the night watch and I was just leaving to get us both some breakfast takeout when we got a call. It was 5 a.m. When I picked up the phone, I heard the distraught voice of a woman say:

MILDRED GURR: I DON’T KNOW WHAT TO DO! My husband and I ate lunch yesterday at this cute little café that I’ve been dying to go to for such a long time but we just haven’t had time because...”

FRIDAY: (interrupting) UH, Excuse me, ma’am, just the facts please!

MILDRED: Oh yes, sorry! Anyway, as I was saying, I DON’T KNOW WHAT TO DO! I am in a wheelchair and if my husband needs to go to a doctor, I can’t get him into the car.

FRIDAY: What seems to be the problem, ma’am?

MILDRED: Well, over an hour ago my husband woke up with real bad stomach cramps. He took two antacids to reduce the pain, but it only seemed to get worse! Now, for the past hour he has been vomiting and has severe diarrhea. I DON’T KNOW WHAT TO DO!!

FRIDAY: Ma’am, it definitely sounds like there is a problem. I’ll stay on the phone to keep you company while Setter Day, my partner, will come to your home to assist you.

MILDRED: (wailing) My husband can’t wait till Saturday comes! He may be dead from dehydration by then!

FRIDAY: Excuse me, ma’am, but Officer Setter Day is my partner. He will come to your home right now to help get your husband to a doctor. He will also need to ask him a few questions.

MILDRED: Thank you, officer that would be nice. My address is 555 Apple Cider Lane, my name is Mildred Gurr, and my husband’s name is Vinnie.

FRIDAY: (to Setter Day, handing over a slip of paper) Go to the home and see if the problem is severe enough to warrant taking Mr. Gurr to the emergency room. Give me a call as soon as you get the answers to the questions we need to solve this case. Good luck!

OFFICER SETTER DAY: (Doorbell rings.) Hello, Mrs. Gurr, I’m Officer Day. How is Mr. Gurr doing?

MILDRED: He’s still running to the bathroom but it seems to be slowing down somewhat.

OFFICER DAY: I imagine he’s pretty tired!

MILDRED: Yes, he is pretty pooped, but these kinds of illnesses seem to do that!

OFFICER DAY: Do you think he’s feeling well enough to answer a few questions? We’d like to make sure this doesn’t happen to anyone else.

MILDRED: Yes, I think so. I have him set up in the spare bedroom and I’ll take you to him. Just remember, though, he may need to visit the bathroom before you’re finished.

OFFICER DAY: I understand! (to Vinnie) Hello, Mr. Gurr, I’m sorry to hear about your illness.

VINNIE GURR: (in a weak voice) Thank you for your concern, officer! I sure don’t know what has happened and why I got sick all of a sudden. I just had a complete physical three days ago and was told I was the picture of good health! Now, look at me! I’m wasting away!

OFFICER DAY: Hopefully we can figure it all out from the answers you give me to a few questions.

VINNIE: I’ll do my best!

OFFICER DAY: Your wife said you both went somewhere to eat lunch yesterday. What did you eat?

VINNIE: Well, I remember I wasn’t very hungry but my wife hadn’t eaten breakfast and was hungry so we went to Sam ’n’ Ella’s, a small café not far from our home. I had an egg salad sandwich, a small green salad and a Coke^®.

OFFICER DAY: Did you notice anything unusual about the food? The way it smelled? The way it tasted? The way it looked? Anything?

VINNIE: Not really, except that the salad wasn’t cold. I also remember seeing them take the sandwich out of an enclosed container sitting on the counter just before they put it on my plate.

OFFICER DAY: Did your wife eat any of the same foods?

VINNIE: No! She ate a complete, hot meal. In fact, I finished eating before she even got her food!

OFFICER DAY: You said you ate at Sam ’n’ Ella’s Café, correct?

VINNIE: Yes, we’d never been there even though it is close to home.

OFFICER DAY: How long ago did you start feeling sick?

VINNIE: Well, let see! We went to the café about 1 p.m. and probably got home around 2:00 p.m. Then, I watched the ballgame on TV, went out and mowed the lawn, came back in and watched the 6 p.m. news, ate a bowl of cereal and milk and went to bed. I guess it was 3 a.m. when I woke up with the stomach cramps. UH OH! You’ll have to excuse me, officer, I gotta go!

OFFICER DAY: (Vinnie returns.) Did you or do you have a fever?

VINNIE: I feel like I do, but I haven’t taken my temperature because our thermometer broke when I dropped it a while back and we haven’t replaced it yet.

OFFICER DAY: Did you or do you now have chills?

VINNIE: Again, I’m not sure! It felt like it at times, but it may have just been from sweating.

OFFICER DAY: Thank you, Mr. Gurr, for the information. We’ll start our investigation right away and let you know what we find. In the meantime, if you feel like eating, only eat a B.R.A.T. diet—bananas, rice, applesauce and toast. Also, since you have lost so much fluid, you need to stay hydrated by drinking water even though you may not feel like it.

Analysis Questions

1. Based on the information given by Mr. and Mrs. Gurr, which bacterium was the probable cause of Mr. Gurr’s illness? Explain the specific reason(s) for your choice. (Hint: Review the Background information.)
2. Which of the food(s) Mr. Gurr ate may have been contaminated? Give one reason for your choice.
3. Why didn’t Mrs. Gurr get sick? 
4. As an employee of the County Health Department, you are required to ensure that food purchased from any eating establishment is safe. What would you recommend that the owners of Sam ’n’ Ella’s Café do to prevent anyone else from getting sick?

Safety Precautions

Although materials in this activity are considered non-hazardous, none of the solutions should be consumed. Wear chemical splash goggles and follow all normal lab safety procedures. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

You have been invited to a buffet-type banquet. Feel free to take one item from each of the six categories of food on the buffet table. Remember which specific “food” items you chose.

1. Select the “food” items you would like to “eat” by placing one spoonful on your “plate”—(inside the cup). Note: Do not take more than one food item from each group. Add “food” to your “plate” using only the spoon that is inside each “food” cup. Do not contaminate the food by mixing up the spoons!
2. When finished filling your “plate” with the six food items, carefully swirl the cup to simulate the mixing of food in the stomach, return to your table/seat and write the name of all of the food items you selected in Column A, Table 1. Note: Do not return to the buffet table(s) to look at anything. Write the list from memory.
3. When everyone is finished taking “food” and writing their list of food items, the instructor will walk around the room and place three drops of an indicator solution into your cup. This will tell you if your food is contaminated, which means that you have been “poisoned” by a bacterial toxin and are sick. Contaminated food = Pink color!
4. As the instructor reads the name of each food item in the buffet, write each name in Column A, Table 1, even if you did not take it.
5. If a pink color in your cup indicates that you are “sick,” raise your hand each time a food item is read that you ate. Count the total number of “sick” classmates who also ate that food, and write the number in Column B: Ate—Sick.
6. If a pink color in your cup indicates that you are “sick,” but you did not eat the food item that is read, raise your hand. Count the total number of “sick” classmates who also did not eat the food, and write the number in Column E: Didn’t Eat—Sick.
7. If a clear color in your cup indicates that you are “healthy,” raise your hand each time a food item is read that you ate. Count the total number of “healthy classmates who ate the same food, and write the number in Column C: Ate—Healthy.
8. Count the total number of “healthy” classmates who did not eat the food, and are healthy in Column F: Did Not Eat—Healthy.
9. When all the columns have been filled in for each food item, calculate the Attack Rate (Column D) for each food item that was eaten, using the following formula:

Note: The number calculated will be a percentage. The “Attack Rate” describes the risk of getting sick for each group of people that ate a particular food.

10. Calculate the Attack Rate (Column G) for each food item that was not eaten, using the following formula:

Note: The number calculated will be a percentage. The “Attack Rate” describes the risk of getting sick for each group of people that did not eat a particular food.

11. In order to determine whether any one food item was responsible for people getting sick, calculate and complete the Relative Risk column:

12. Analysis: Any food item with a Relative Risk >1 suggests that a food item was the probable cause of the illness. However, if more than one food item has a Relative Risk >1, the food item with the largest Relative Risk is the most likely cause. A Relative Risk <1 suggests that a particular food item may have provided some protection against getting sick.
13. All solutions used in this lab can be disposed of down the drain with plenty of running water. Thoroughly rinse and dry your cup.

Student Worksheet PDF

10690_Student1.pdf