BIOS 242 Week 3 Micro Gram Staining Lab

BIOS 242 Week 3 Micro Gram Staining Lab

Student Name

Chamberlain University

BIOS-242 Fundamentals of Microbiology

Prof. Name:

Date

Lab 3: The Gram Stain: Identify and Differentiate Bacteria

Learning Outcomes

Upon completing this lab, you should be able to:

1. Describe the structural differences between Gram-positive and Gram-negative bacteria.
2. Identify both the theoretical and technical aspects of the Gram staining procedure.
3. Recognize common errors in the Gram staining process.
4. Analyze the results of a Gram staining experiment using a light microscope.

About the Gram Stain: Identify and Differentiate Bacteria Virtual Simulation Lab

Did you know that there are approximately 5 million-trillion-trillion bacteria in the world? While most of these bacteria are harmless, some can lead to diseases in affected hosts. This simulation allows you to help doctors identify bacteria in a cerebrospinal fluid sample from a patient suspected of bacterial meningitis. You will explore the differences between Gram-positive and Gram-negative bacteria by constructing 3D models of bacterial cell walls on a hologram table. You will also enter an exploration pod to witness how the four reagents of the Gram stain interact with these structural components to color the bacteria.

Perform the Gram Stain

When the patient’s fluid sample arrives in the laboratory, you will equip yourself with protective gear and prepare a bacterial smear, heat-fix it to a glass slide, and perform the Gram stain in a safe virtual environment. If you make a mistake, you can repeat the procedure until you become proficient at it. Finally, using a light microscope, you will interpret the results of your Gram stain by viewing the microscopic image on a computer screen. You will also apply immersion oil to increase magnification to 1000x, helping you identify the presence of any bacteria in the patient’s cerebrospinal fluid.

Table: Gram Staining Process and Prediction of Colors

Questions

1. Purpose: Please describe in complete sentences and in your own words, the purpose of this experiment.
   The purpose of this experiment is to determine the Gram stain of the bacterial sample. This procedure helps determine the chemical composition of the bacterial cell wall. The resulting stain color will indicate whether the bacterium is Gram-positive or Gram-negative. Additionally, the Gram stain can be used to analyze the shape, size, and arrangement of bacterial cells.

2. Describe what happened in the following scenarios:

   • A fellow student showed you a Gram-stained slide where cells containing thick cell walls were stained pink. What would you tell her about the staining procedure?
     If cells with thick cell walls are stained pink, an error occurred during the procedure. The mistake likely happened in the iodine step, which was skipped. Normally, iodine binds with crystal violet in Gram-positive bacteria, making the stain more permanent. Without iodine, the bacteria were not properly stained, and Safranin stained them pink instead.

   • A fellow student showed you a Gram-stained slide where cells containing LPS (lipopolysaccharide) were stained purple. What would you tell her about the staining procedure?
     If Gram-negative bacteria containing LPS are stained purple, it indicates an error occurred during the decolorization step. Gram-negative bacteria have a thin cell wall and an outer membrane containing LPS. Without the decolorization step, the crystal violet and iodine remained in the cells, causing them to appear purple.

3. Reflection: Write five sentences on what you learned from this simulation. What did you like and what would you prefer not to be a part of this simulation?
   In this lab simulation, I learned about the structural differences between Gram-positive and Gram-negative bacteria and how their cell walls affect the staining process. I discovered why these bacteria stain different colors based on components like peptidoglycan and the thickness of their cell walls. I also learned the steps of performing a Gram stain and was able to replicate the procedure myself. Additionally, I had the opportunity to use a microscope to distinguish between Gram-positive and Gram-negative bacteria, considering their structure, size, and arrangement. I appreciated how informative the simulation was and how it provided a realistic experience, but I would have preferred less repetitive steps when practicing the staining procedure.

BIOS 242 Week 3 Micro Gram Staining Lab

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