Microbiology Lab Report – Gram Staining

The lab report is for microbiology and I have 8 reports due; each a different topic. Below are the instructions for the
first one.

LAB REPORT 1- Selected questions from Exericse 3-6 (Gram stain)
Note: This is turned in after you have viewed your Gram stain slides.
In your results, please remember to tell me which one(s) of the 3 you are working with in this exercise are Gram positive or Gram negative, what are their bacterial shapes and how they are arranged..
Bacteria for this exercise are: Escherichia coli, Bacillus subtilis, and Staphylococcus epidermidis (or S. aureus)

Q1. What are the chemical (structural) differences between the cell walls of gram-positive and gram-negative bacteria that might explain differences in the rate of decolorization? In gram-negative cells, there are two structures that need to be mentioned. And note: We are not referring to the gram stain procedure itself.
Q2. In what way does the age of a culture affect the Gram stain reaction? Explain why.
Q3. Predict the effect of the following 4 mistakes made when performing a Gram stain. Consider each mistake independently and explain your answers.
a) failure to apply the iodine b) failure to apply the decolorizer
c) failure to apply the safranin d)reversal of order of crystal violet and safranin stains
Extra Credit (and you will need to know this for the lecture exam 2)
Q.4. List FOUR chemical and/or structural differences that distinguish gram-positive from gram-negative bacteria? Note: We are not referring to the Gram stain procedure itself.

Note: For lab exam should: I) Predict what would happen if you apply the decolorizing agent for too short a time? Too long a time? II) understand why Gram stain is a differential stain procedure and not a simple stain procedure III) understand how/why bacterial structures of Gram positive and Gram negative bacteria contribute to their differentiation by the Gram staining process (related to this: would the terms Gram positive/Gram negative apply to a eukaryotic cell such as an epithelial cell?)
Reminders: Besides knowing the various functions of the light microscope parts, you should know what the term resolution is about (& threshold value for light microscope) and what is the purpose of immersion oil for the 100X objective lens. Last, what kind of stain is safranin and crystal violet? What charge do these stains have and what type of molecules do they bind to with respect to charge Also should know terms parcentric, parfocal, field of view, depth of focus.

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