What is analysed?

A Gram stain is a laboratory technique used to identify the presence of bacteria within areas of the body typically considered sterile.

What does the result mean?

The result of a Gram stain indicates the type of bacteria causing an infection, providing information about the bacterial morphology (shape). Bacteria are classified as either Gram-positive or Gram-negative based on their cell wall composition.

Viruses aren’t visible under a Gram stain because they lack a cell wall, which is essential for staining.

Why conduct the analysis?

A Gram stain is conducted to determine the cause of a bacterial infection to then help determine the course of treatment for the bacterial infection.

When to conduct the analysis?

A Gram stain is conducted when a bacterial infection is suspected. Symptoms of a bacterial infection may include skin inflammation, red or painful skin, or a wound that doesn’t seem to heal.

What sample is required?

A sample of skin swab or any fluid/pus from the infection site is required.

Is any prior preparation necessary?

No prior preparation is necessary.

How is it performed?

The sample is sent to a laboratory, where it is smeared on a glass slide and left to dry. A series of stains (dyes) including crystal violet, iodine, alcohol (or acetone), and safranin are then applied to the glass slide.

After staining, the glass slide is examined under a microscope. Gram-positive bacteria appear purple, while Gram-negative bacteria appear pink or red.

What are the normal values?

The results of a Gram stain are qualitative, indicating only whether bacteria are Gram-positive or Gram-negative.

What does having altered values mean?

• Gram-positive bacteria: Typically include bacteria such as Staphylococcus aureus and Streptococcus pneumoniae. These bacteria have a thick peptidoglycan layer in their cell wall.
• Gram-negative bacteria: Examples include Escherichia coli and Pseudomonas aeruginosa. They have a thinner peptidoglycan layer and an outer lipid membrane.