How Does Staphylococcus Aureus Appear After Gram Staining?

Staphylococcus aureus is one of the most important human pathogens causing infections from the superficial to the systemic. Boils, impetigo, wound infections and pneumonia are some examples of its pathology. One of the first steps in the identification of S. aureus is the gram stain. The gram stain of S. aureus is classified as gram-positive cocci in clusters.

Gram Stain

• The gram stain is a differential stain that divides most bacteria into two groups: gram positive (blue) and gram negative (pink). The prepared stained slide is examined microscopically to determine which group it belongs to. The bacterial cell wall has a direct, practical importance in the gram stain procedure.

Procedure

• The gram stain procedure consists of four stains or reagents. Crystal violet, the purple primary stain is flooded on the microscope slide containing the specimen. The bacterial cell is filled with the purple dye. Next is the mordant, Gram's iodine which serves to bind the dye. Then a decolorizing reagent is added and, depending on the cell wall, either the purple will be retained (gram positive) or the bacteria will lose the purple dye (gram negative). Lastly, the counterstain Safranin is added and fills the empty gram negative cells giving them the pink color.

Cell Wall

• Certain properties of the cell walls of bacteria result in different staining reactions with the gram stain technique. The cell wall of Staphylococcus aureus, like most gram-positive bacteria, contain a thick layer of peptidoglycan giving the bacteria the ability to retain the purple primary stain.

Morphology

• The cell morphology of Staphylococcus aureus is spherical in appearance. Spherical bacterium are known as coccus. Based on the way all Staphylococcus species divide, they can show very distinctive arrangements. Because Staphylococcus aureus divide on two of more planes, arrangements of bacterial tetrads and clusters are characteristic.

Final Appearance

• After performing a gram stain procedure on a specimen that contains Staphylococcus aureus, the stained slide will appear as a gram-positive cocci in tetrads and clusters microscopically.