Core Microscopy Skills: Instructional Scaffolding for the Gram Stain
In the laboratory component of many life science courses, students frequently have difficulty gaining familiarity with the microscope and becoming comfortable in its use. It is often challenging for first time microscope users to learn staining methods and microscope technique within a short period of time when they have not yet mastered the more basic skills, such as focusing the microscope and fixing a sample. Here we implement a stepwise process to aid the student in familiarity with the use of the microscope as well as to increase the success rate with which they are able to stain and view microorganisms. This instructional scaffolding can allow students to master several skills before combining them and increase understanding of foundational methods such as the Gram stain.
Students will learn foundational skills in microscopy, including operation of a compound microscope, focusing on a sample, preparing a wet mount, making a smear, heat fixation, simple staining, and Gram staining.
Context for Use
Proficient microscopy skills are essential for success in various disciplines in the biological sciences and even in select career fields. Multiple biology laboratory courses include use of the microscope. Thus, it is important that high school and college students be able to learn the basic skills of staining and microscopy with confidence and be able to adequately perform complex stains. In particular, the Gram stain is a procedure almost universal in general biology and microbiology labs. Yet often, when students are asked to perform the Gram stain, the success rate is low, particularly on the first pass. This is due, in part, to the Gram stain consisting of multiple skills and techniques of microscopy combined into one procedure. Instead of requiring students to master all of the necessary skills simultaneously, it is more effective to use a sequential process that separates the components of the procedure (Form and Lewitter, 2011). At the beginning of learning something new, students are often distracted by a focus on not making mistakes (Ericsson, 2004). The design of this activity allows students to concentrate on a few skills at one time, and by requiring that each stage incorporate the skills from previous stages, promotes students to confidently work their way up to the complex differential staining procedure. We implement this activity early in the semester in a university sophomore-level microbiology course, however it is appropriate at earlier levels, including high school.
Full description of lab activity, with time estimates for each stage and common student errors. Procedure (Acrobat (PDF) 148kB Oct24 16)
Worksheet for students to review parts of a microscope before the lab. Pre-Lab Activity (Acrobat (PDF) 163kB Oct24 16)
Supplies for the Lab (Acrobat (PDF) 24kB Oct24 16)
Description for Instructor (Acrobat (PDF) 13kB Oct24 16)
Teaching Notes and Tips
Basic instructor notes are in the procedure document, with detailed notes in the description for instructor.
We have not performed official assessment of this laboratory exercise. Instructors may assess student learning using written quizzes for basic facts or lab practical assessments, such as performing a stain or smear, to determine skill acquisition. Anecdotal feedback from students indicates that this scaffolded design, in contrast to the typical approach of asking students to perform a Gram stain in a single step, is more achievable and less stressful.
References and Resources
1. Emmert, E.A.B. (2013). Biosafety Guidelines for Handling Microorganisms in the Teaching Laboratory: Development and Rationale†. J. Microbiol. Biol. Educ. JMBE 14, 78–83. available http://www.asmscience.org/content/journal/jmbe/10.1128/jmbe.v14i1.531 and revised with a webinar at http://www.asm.org/index.php/education-2/22-education/8308-new-version-available-for-comment-guidelines-for-best-biosafety-practices-in-teaching-laboratories
2. Ericsson, K.A. (2004). Deliberate Practice and the Acquisition and Maintenance of Expert Performance in Medicine and Related Domains. J. Assoc. Am. Med. Coll. 79, S70–S81.
3. Form, D., and Lewitter, F. (2011). Ten Simple Rules for Teaching Bioinformatics at the High School Level. PLoS Comput Biol 7, e1002243.