Gram staining.

• Gram stain is used to differentiate the microorganism whether it is gram-positive or gram negative.
  
  
  
• Gram positive -Purple
  Gram negative- Pink
  
  
• It is conducted when the urine or swab culture have mixed growth of bacteria.
  
  
• For urine or stool culture, it is normal to have both gram-positive and gram-negative bacteria present in the culture.
  
  
• Except for stool, if there are more than 10 colonies appeared in other types of culture on blood agar, gram staining will be carry out for species identification.

Procedure:

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1. Prepare a smear and fix it by passing through gentle heating.
2. Flood the smear with crystal violet for 1 minute.
3. Rinse with running tap water.
4. Flood the slide with iodine for 1 minute.
5. Rinse with running tap water.
6. Flood with decolorizer for 30 seconds.
7. Rinse with running tap water.
8. Counter stain the slide with safranin for 1 minute.
9. Rinse with tap water and dry the slide.
10. Observe under 100x with immersion oil.

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Reference:

1. http://www.medicinehack.com/2012/02/gram-staining-procedure-mechanism.html
2. Labtestsonline.com