Modeling and Visualizing Bacterial Colony Purification Without the Use of Bacteria or Laboratory Equipment

Abstract

Microorganisms typically exist in diverse and heterogeneous communities within their various environmental niches. The isolation of an individual species from these communities is an essential laboratory skill to study of the properties and behaviors of that organism. To achieve this separation, the “quadrant streak” for single colony purification is often included in undergraduate microbiology laboratory curricula. To aid student mastery of this technique, I have developed a simulated culture purification activity that allows students to immediately visualize the dilution and separation of an artificial microbial community with the goal of isolating purified colonies. This tool uses readily available, inexpensive, art supplies to simulate a mixed bacterial culture. The “mixed culture” consists of craft glitter of at least two distinct colors, held together with water-soluble, highly pigmented watercolor or gouache paint. Students practice aseptic technique by using a paintbrush to mimic an inoculating loop to streak and dilute the culture on a piece of cardstock. Sterilization of the “loop” is simulated by rinsing the brush. Students will immediately self-assess whether they are correctly performing the quadrant streak, rather than having to wait until the next laboratory session for bacteria to grow, which may allow them to master the technique sooner.