Parasitology as a Teaching Tool: Isolation of Apicomplexan Cysts from Store-bought Meat

Abstract

Our goal was to design a bench experiment tailored to the environment of advanced high school biology, college freshman biology, and nonmajor labs. To accomplish this goal, we developed a scientific protocol for isolation of apicomplexan cysts from store-bought meat by adapting existing protocols (Cornelissen et al., 1981 ; Blewett et al., 1983 ; Dubey, 1992 , 1998 ; Omata et al., 1997 ; Garcia et al., 2006 ). The majority of buffers used were common chemicals found in many introductory biology laboratories, and the protocol is simple enough for a freshman to use. What we found to be most challenging was modifying the experiment to fit time constraints imposed by a typical high school schedule. This experiment takes ∼3 h. We found that the lab could be split up into 4 d for high school and 2 d for college. The teacher should make some initial preparations (i.e., making buffers and solutions) to shorten the lab period. We suggest that students split up into at least five groups of six students each. The students should be encouraged to compare and share their results. We recommend that the students spend time researching T. gondii statistics on the CDC website (www.cdc.gov) and reading newspapers to identify related topics, such as food recalls as a result of tainted product. Specifically, we suggest creating a quiz to test their knowledge of food safety and administering it before and after the exercise. We would also suggest including a follow-up discussion section investigating student response to this assignment. For example, how has completing this laboratory exercise affected their opinions about food, science, and laboratory experiments? We have listed several very useful websites in Materials and Methods. These sites are extremely helpful in providing pictures for identification purposes and background information on the parasites themselves. In addition to T. gondii, numerous other organisms (i.e., multiple types of nematodes and tapeworms) can be observed by sampling the bottom of the meat slurry instead of the supernatant. Although we had multiple years of experience at the lab bench, we found that we were surprised by the abundance and diversity of organisms in meat. It provoked us to ask the question: “Just who is eating who?” Although many of these pathogens are species specific and thus not a health threat to human (i.e., N. caninum), some of the organisms, such as T. gondii, are human pathogens. We realized that it reinvigorated our interest in the topic, and we were fascinated by the images in the microscope. Some of us could not eat meat for a week after doing the experiment. This realization validated for us the idea that science at the bench as opposed to simple book learning is essential for biology and nonmajors students alike. It drives home the point that well-prepared foods (washing and cooking) are a cornerstone of food safety. Carrying out this experiment familiarizes students with the microscope and more advanced isolation techniques such as the use of Percoll. It introduces some concepts about parasitology and food safety. It can be incorporated into a lesson plan covering infectious agents or health. It meets Indiana secondary school standards for advanced life sciences (standard 2: health, safety, and microbiology of food), and human anatomy and physiology (standard 10: immune mechanisms). Completion of this exercise also meets national educational standards for secondary school in the topics science as inquiry, interdependence of organisms, personal and community health, and science as a human endeavor (National Committee on Science Education Standards and Assessment, 1996 ). Upon completion of this exercise, the following positive outcomes are expected for students: 1) gain confidence about ability to carry out labwork and stimulate curiosity about pursuing other science classes, 2) obtain insight about health and safety of food and provide students the chance to critically evaluate articles in the newspaper regarding food recalls, and 3) change student behavior in terms of food choice, food preparation behavior, or both. In sum, the ultimate outcome of this exercise is for students to apply the procedure to investigate a real and meaningful problem and, as a result, to describe organisms found in the meat supply, the hazards they pose, and procedures for avoiding the hazard. Because there is a compelling repulsion factor, there is a strong possibility that students would also change their behavior (either food choices or food preparation behavior). For teachers, it represents an innovative teaching strategy that provides a relatively inexpensive laboratory experience with direct student involvement that meets several national education standards.