What are the morphological characteristics of staphylococcus aureus?

1. Microscopic morphology:
S. aureus cells are Gram-positive and appear in a spherical shape. They are often in clusters resembling a bunch of grapes when observed under a light microscope after Gram staining. The name ‘Staphylococcus’ was derived from Greek, meaning a bunch of grapes (staphyle) and berry (kokkos). The scanning electron microscopic observation reveals roughly spherical-shaped cells with smooth surfaces. The diameter of the cells ranges from 0.5 to 1.0 μM. The transmission electron microscopy of cells shows a thick cell wall, distinctive cytoplasmic membrane, and amorphous cytoplasm.

2. General cultural and biochemical characteristics:
S. aureus is an aerobic and facultative anaerobic organism that forms fairly large yellow or white colonies on nutrient-rich agar media. The yellow colour of the colonies is imparted by carotenoids produced by the organism. The term ‘aureus’ is derived from Latin, which refers to the colour of gold. The organism is often haemolytic in blood agar due to the production of four types of haemolysins (alpha, beta, gamma, and delta). Nearly all isolates of S. aureus produce coagulase enzyme, a virulence factor that also helps in the identification of the organism. The organism is salt tolerant and is able to grow in a mannitol-salt agar medium containing 7.5% sodium chloride. The organism is catalase-positive and oxidase negative.