gram stain technique

• what technique can be used to classify bacteria


  the gram stain technique
• what are the two types of bacteria being differentiated by the gram stain reaction


  gram positive and gram negative
• why do different types of bacteria stain differently


  this is due to differences in the chemical composition of their cell walls
• what is the general structure of the cell wall


  a mixture of polysaccharides and polypeptides
• what does a cell wall make the cell immune to(or protects against)


  swelling and bursting(lysis) because of osmosis
• what gives the cell wall the strength to stop the swelling caused by osmosis


  the cross linkages between the layers
• what is the first step of the gram stain technique


  place a drop of distilled water onto a microscope slide
• during the gram stain technique what happens after a drop of water is places on the microscope slide


  use a flame to sterilise an inoculating lop and allow to cool
• during the gram stain technique what happens after the inoculating loop is sterilised


  remove the lid of the plate culture and gently touch a colony of bacterium using the sterile loop.
• during the gram stain technique what happens after you have dipped the sterile loop into the colony of bacterium


  rotate the loop in the distilled water on the slide to form a smear ,then re-sterilise the loop.
• during the gram stain technique what happens after you have smeared the bacterium on the slide


  allow the smear to dry in the air and the heat fix the slide
• during the gram stain technique how do you heat fix the slide


  pass the slide through a flame three times(keep the smear facing upwards)
• during the heat fix process what must you not do and why


  not hold the slide directly in the flame because it will smash
• during the gram stain technique what happens after you have heat fixed the slide


  when the slide has cooled , cover the smear with the crystal violet(purple dye) and let it stand for 1 minuet
• during the gram stain technique what happens after after you have added the crystal violet dye to the heat fixed slide


  rinse the slide gently with water using a pipette and drain until the colour runs clear
• during the gram stain technique what happens after the crystal violet dye runs clear


  cover the slide with grams iodine and let it stand for 1 minuet
• during the gram stain technique what happens after the slide is covered with grams iodine


  tilt the slide over a beaker and drip alcohol over the surface until no more purple colour runs out
• when tilting over a beaker and drip alcohol what must you not do


  using too much alcohol will remove the whole stain
• during the gram stain technique what happens after the slide has been tilted over a beaker and alcohol has been dripped


  rinse the slide with water again and drain , add safranin counter stain and leave for 1 minuet
• during the gram stain technique what happens after safranin counter stain has been added


  rinse the water and blot the surface very carefully using filter paper
• during the gram stain technique what happens after the safranin has been blotted


  examine the slides under oil immersion(x100 objective lens)