An Instructor’s Ultimate Assessment: The Bacterial Unknowns Project
“You’ve never experienced anything like the bacterial unknowns project”, a veteran colleague said to me after I received my very first professional appointment as a microbiology adjunct professor. Six years later, these words still resonate in my head, and I often find myself reciting them to my students on the first day of the semester while discussing the course project. Mentioning the word “project” on the first day of class is not the most favorable conversation to have with students. However, the bacterial unknowns project may just be the ultimate assessment an instructor can implement in the microbiology laboratory.
At the start of the project, each student receives one test tube that contains two different bacteria species, one gram negative and one gram positive. Students are provided a list of ten species and informed that they have two out of the ten possible organisms in their test tube. The objective of this inquiry-based project is to have students plan an investigation in which they execute varying diagnostics tests to generate scientific evidence used to identify their unknown gram positive and gram negative, and provide data to support the elimination of the eight other species. Students are also informed that the role of the instructor in the project is merely to serve as an assistant when needed and to provide guidance when roadblocks are encountered. In terms of resources available to the students, the use of differential and selective media is limited to the biochemical assays taught in lab earlier in the semester. Such assays include the use of Triple Sugar Iron Agar, Litmus Milk Media, Blood Agar, Urea Broth, Gelatin Agar, Phenol Red Broths with different Carbohydrate sources, Mannitol Salt Agar, and Eosin Methylene Blue Agar. Students can perform any of these tests, but must complete a minimum of 5 tests to confirm the identities of their bacteria. This is critical given that molecular techniques are not used in confirmation of the bacteria due to costs and the overall objective of this project, which is using diagnostic tests to identify bacteria species.
The bacterial unknowns project can be deemed as an ultimate assessment because it requires repetition of lab techniques and the development of fundamental microbiology laboratory skills such as aseptic transfer, media preparation, staining techniques, bright-field microscopy, and differential testing, all so that students can identify their unknown cultures. For example, one lab technique that students must be able to execute in the beginning of the project is streaking for isolation, which allows students to isolate their gram negative bacteria from the gram positive bacteria. A student will often find this technique to be the most challenging to master. The inability to achieve isolation prevents the student from developing pure colonies to produce stock cultures of their unknowns and thus sets the student behind on their project schedule. Being in such a predicament only leaves the student with one strategy to follow; which is to repeat the procedure and try again for isolation.
Lab skills really tend to mature the most during the unknowns project due to the repetition factor. Other lab skills that are repeatedly tested and strengthened during this project include microscopy skills and staining techniques. For neophytes to the field, a big challenge to studying microorganisms is gaining the tacit knowledge to quickly and correctly focus a bright-field light microscope and to carryout gram stains on different colonies of potential bacterial suspects. Throughout this inquiry based investigation, it is all too common to hear students request assistance from their instructor to view their gram stained specimens, and to consult with their instructor on the bacterial shape and cell arrangements of their specimens. These requests are higher in demand in the early stages. However, by the middle of the project, these requests become fewer and fewer, with instructors often impressed at how quickly the students transform to independent undergraduate researchers; this can happen in a matter of days.
Prior to starting the project, students are given information on how they will be assessed. In my courses, students are not merely assessed on their ability to identify their unknown cultures. With the project being the ultimate assessment of the students’ microbiology laboratory skills, I believe it is fair to grade my students on several facets of this project. My grading criteria includes assessing the planning and experimental design of the students’ projects, student adherence to BSL-2 Laboratory Safety Regulations, student execution of microbiology laboratory techniques, student communication with the instructor, and finally the completion of the formal lab report. I find grading students in these areas helps to engage them in the entire process of the investigation versus having students solely concerned with simply identifying their two species correctly. In other words, if a student does not correctly identify their microorganisms, they do not fail the project in its entirety.
Using these grading criteria allows students to act like lead investigators by carrying out independent research. The students are responsible for their own experiments, the planning of their own time spent working in the laboratory, justifying their use of lab materials, and constructing their results and conclusions in the form of a research paper. The unknowns project is a terrific critical thinking experience that really allows students to strengthen and ultimately master all of the fundamental laboratory techniques learned throughout the semester; it also provides students with experience in leading their own inquiry-based science project. In fact, I have had several students enjoy their experience with this project so much that they seek out other opportunities to conduct undergraduate research in microbiology.