Objectives: Sample, culture, and identify the bacteria growing on a kitchen sponge; practice skills in light and electron microscopy; write a basic lab report (introduction, methods, results, discussion).
Instructions
Go to your kitchen sink and look at your sponge. When’s the last time you replaced it? Is it worn, shredded, and loaded with gunk? In this lab, we’ll be sampling our kitchen sponges for common bacteria and examining them with both light and electron microscopy. Well, this is a simulated lab, so you won’t be looking at your own kitchen sponges… but I’d like you to pretend that you are, so this activity is equal parts science and imagination!
First, review the “Sampling Bacteria” and “Basic Microscopy” chapters in the Module 2 Resource Book to study the techniques we’ll be practicing for this lab activity. Next, using NC BioNetwork’s virtual compound microscope (ncbionetwork.org/iet/microscope), click “Explore” and pull the “Acid Fast Mix” slide from the slide box. Drop down to the 100x objective (oil immersion lens), find a representative field of view (FOV) on the slide, and take a screenshot so that only the FOV is visible (not your entire browser window!); on Mac, press command+shift+F4 to select an area to screenshot (Windows: Windows key+shift+S; Chromebook: shift+control+show windows). OPTIONAL: Then, using Myscope Explore’s virtual SEM (myscope-explore.org/virtualSEM_explore.html), compare the “unused kitchen sponge” and “kitchen sponge with microbes” (1 or 2) samples, which are located in the “Everyday Things” dropdown menu. Choose an appropriate accelerating voltage and make a note of this (because it’s an important detail to include in the methods section of your lab report, whereas spot size and Z height distance are not). Select a suitable level of magnification and be sure to use a similar magnification for both samples; if you’re having trouble getting your image in focus, instead of dragging the slider with your mouse, click the slider and use the left and right arrow keys on your keyboard. Finally, instead of taking screenshots, click the “SAVE” button to download your image along with the scale bar.
Your lab report will include an introduction, methods, results, discussion, and references. The introduction is a brief overview of the background and reasoning for the project; in this case, what kind of bacteria might be growing on our household kitchen sponges (and why should we care?); include in-text citations to any references you use. For the methods section, you can paraphrase the bacterial sampling methods and microscopy techniques covered in the Module 2 Resource Book). Next, the written results section should include one or two figures; Figure 1 should show the results of your bacterial culture from your sponge under the light microscope (the acid fast stain, 100x objective); OPTIONAL: Figure 2 should have two subpanels (2a and 2b) comparing clean vs. dirty sponges under the electron microscope. The discussion should provide an interpretation of your findings and the broader context and/or applications; as part of this, you should discuss the one required reference (listed below) as well as at least one other peer-reviewed source (I’ve included two suggestions, but you can pick something else); include in-text citations. Full references in the references section should be organized alphabetically by the surname of the first author; use hanging indents and follow all APA formatting rules [Lastname, F. M. (Year). Article title in sentence case. Journal Name, volume#(issue# if there is one), page range xx–xx. DOI].
Required References
- Cardinale, M., Kaiser, D., Lueders, T., Schnell, S., & Egert M. (2017). Microbiome analysis and confocal microscopy of used kitchen sponges reveal massive colonization by Acinetobacter, Moraxella and Chryseobacterium. Scientific Reports, 7, 5791. https://doi.org/10.1038/s41598-017-06055-9
Suggested References
- Møretrø, T., Ferreira, V. B., Moen, B., Almli, V. L., Teixeira, P., Kasbo, I. M., & Langsrud, S. (2022). Bacterial levels and diversity in kitchen sponges and dishwashing brushes used by consumers. Journal of Applied Microbiology, 133(3), 1378–1391. https://doi.org/10.1111/jam.15621
- Wolde, T., & Bacha, K. (2016). Microbiological safety of kitchen sponges used in food establishments. International Journal of Food Science, 1659784. https://doi.org/10.1155/2016/1659784
Deliverables
A 700-word (~2 pages, including figures and references) typed report. Use 12-point doubled-spaced Times New Roman font. No title or cover page is necessary, but there should be headings for the Introduction, Methods, Results, Discussion, and References sections. References should be formatted in APA style, which includes the use of in-text citations. Name the file “Micro_Lastname” and upload as a standard Word document (.docx).
| Introduction A brief but relevant background of the topic as well as the purpose for the study is provided (the purpose is not “to do the lab” or “to learn techniques”—pretend we’re actually testing the sponges for bacteria); language and use of biological terms is appropriate for a college-level audience Maximum score 5 |
| Methods The protocol for collecting bacterial samples is described with enough detail for someone to replicate the study; the procedures for investigating microbe morphology with light (and OPTIONAL: electron microscopes) are accurate, with relevant technical details (e.g., cell stains) Maximum score 2.5 |
| Results Major results (i.e., bacteria species identified, comparison of unused vs. dirty sponges) are explained in paragraph format (figures can never stand alone!); Figure 1 shows the image captured from the compound light microscope; figures include a descriptive legend (caption/title); OPTIONAL: Figure 2 shows both unused (2a) and dirty (2b) sponges as seen under SEM, and the images include scale bars Maximum score 10 |
| Discussion Interpretation(s) of key results are provided; results are compared to or placed within the existing body of scientific literature (including relevant, specific details from any referenced publications); the broader context and/or applications of the results are discussed, returning to the overall purpose of the study Maximum score 10 |
| References The report includes 2 peer-reviewed references (including the one required reference provided); all references are formatted following APA style guidelines; in-text citations are used when necessary Maximum score 2.5 |
