Gram stain of skin lesion

Gram Staining of Skin Lesion

Gram staining is a laboratory technique used to determine whether bacteria are gram-positive or gram-negative. Gram staining is used to differentiate bacteria and to diagnose bacterial infections on skin lesions. Gram staining of skin lesions is especially useful in cases of acne, impetigo, and cellulitis.


Before a Gram stain is performed on a lesion, the area should be cleaned with soap and water and allowed to dry. Then, the lesion should be swabbed with a sterile cotton swab and wiped on a microscope slide.


  • The sample is heat-fixed to the slide.
  • Gram's Crystal Violet is added, using a dropper.
  • The slide is flooded with Iodine for one minute.
  • The sample is flooded with an Acetone-Alcohol solution.
  • The slide is stained with Safranin for one minute.

Types of Bacteria Seen

Gram stains can distinguish two main types of bacteria, gram-positive and gram-negative. Gram-positive bacteria are bacteria that have a thick, multiple-layered cell wall, while gram-negative bacteria have a single-layered cell wall. Gram-positive bacteria will retain the crystal violet dye after the alcohol decolorization step, while gram-negative bacteria will be decolorized. Examples of gram-positive bacteria are Staphylococcus, Streptococcus, and Bacillus species and examples of gram-negative bacteria are Escherichia, Pseudomonas, and Proteus species.


Gram stains are generally considered to be safe as they are not invasive. However, As with any medical procedure, allergic reactions are possible. It is recommended to consult a doctor before the procedure if there is any existing allergies.

Why Use Gram Stain

Gram staining is an important technique used to identify the bacterium causing infections. It is important for doctors to be able to distinguish between the different types of bacteria since they can respond differently to treatments. Additionally, gram stains can be used to differentiate between normal flora and pathogens, helping to pinpoint the infection.

When to Use Gram Stain

Gram staining is most often used in cases of skin infections, such as acne, impetigo and cellulitis. It can also be used to diagnose more serious infections, such as sepsis. Additionally, doctors may also use Gram stains to diagnose urinary tract infections.