Using an “Unknown Characterization” Activity as the Midterm Lab Practical in a Large Enrollment, Multi-Lab Section Microbiology Course

The characterization and identification of “unknowns” is an often-used laboratory activity in microbiology courses. As course enrollments become large, the logistics of providing unknown culture mixes, tubed and plated culture media, plus incubator and refrigerator space become quite daunting. A few years ago we discontinued the three-week Unknowns lab exercise when enrollment reached 240 or so students. In its place we have developed an hour long, midterm lab practical that incorporates smear preparation and the Gram stain, biochemical media, rapid tests, and a streak plate. This easy-to-grade laboratory assessment tool has taken the place of the more traditional station-to-station lab practical, and has worked well for the instructors responsible for administering practicals to 480 students in 13 lab sections over a two-day period