GRAM STAINING

• Isolation Streak Plates


  1. Utilize aseptic (sterile) technique to spread bacteria sample on medium

  2. Prevent contamination while transferring bacteria from source plate to specialized media plates
• Growth Media/Nutrient Medium


  Provide nutrients, moisture, and pH for microbial growth
• Tryptic Soy Agar (TSY)


  • Complex nutrient medium supporting the growth of various microbes
• Medium preparation


  1. Dry powdered medium mixed with water

  2. pH checked

  3. Dispensed into bottles

  4. Autoclaved (sterilized)
• Autoclave


  Exposes medium to high temperature (121°C) and pressure (15 psi) for 20 minutes, sterilizing it
• Gram Stain


  • Developed by Christian Gram in late 1800s
  • Differential stain separating bacteria into Gram-positive (stain purple) and Gram-negative (stain pink) groups
  • Illustrates differences between bacterial cells
  • Provides rapid identification of bacterial morphology and Gram reaction
• Bacterial Smear for Gram Staining


  Preparation includes unknown bacterium, Gram-positive (GP), and Gram-negative (GN) controls
• Bacterial Controls


  • Samples with known identities subjected to same procedures as unknown sample
  • Provide basis of comparison and indicate if procedure was performed correctly
• Bacterial Control Examples


  • Staphylococcus epidermidis (Gram-positive control)
  • Escherichia coli (Gram-negative control)
• Control Media


  Test tubes containing media are autoclaved, cooled, and solidified with expanded surface area of slant
• Key Terms


  • Acid Fast Stain
  • Agar
  • Aseptic Technique
  • Autoclave
  • Counterstain
  • Culture Medium/Media
  • Decolorizer
  • Differential Stain
  • Gram Negative
  • Mordant
  • Gram Positive
  • Negative Control
  • Gram Stain
  • Positive Control
  • Isolation Streak Plate
  • Primary Stain
• Gram-staining is important because it is a common laboratory test that can help diagnose the presence of a bacterial infection quickly
• Aseptic transfer


  The process of transferring a substance without introducing any contaminating bacteria or fungi
• Aseptic transfer is crucial because it helps maintain the purity of the substance being transferred, ensuring accurate results in experiments or tests
• Isolation streak plate


  Involves streaking a sample across a growth medium in a pattern that gradually dilutes the sample, allowing individual cells to be separated from each other to obtain a pure culture of microorganisms