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.