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Morphology of necrotic cell: A) Cytoplasmic changes: -Increased eosinophilia – Due to denatured proteins and loss of cytoplasmic RNA. -Glassy homogenous appearance – loss of glycogen particles. -Moth eaten appearance of cytoplasm – enzymatic digestion of cytoplasmic organelles. -Whorled phospholipidRead more
Morphology of necrotic cell:
A) Cytoplasmic changes:
-Increased eosinophilia – Due to denatured proteins and loss of cytoplasmic RNA.
-Glassy homogenous appearance – loss of glycogen particles.
-Moth eaten appearance of cytoplasm – enzymatic digestion of cytoplasmic organelles.
-Whorled phospholipid masses derived from damaged cell membranes – myelin figures.
-Calcifications – fatty acids derived from phospholipid masses.
B) Electron microscopic findings: Necrotic cells are characterized by-
-Discontinuities in plasma and organellar membrane.
-Swollen mitochondria with large amorphous densities.
-Intracytoplasmic myelin figures.
-Aggregates of fluffy material representing denatured proteins.
C) Nuclear changes: Due to the non-specific breakdown of DNA, 3 patterns are identified-
-Karyolysis – fading of basophilia of chromatin due to enzymatic degradation of DNA by endonucleases.
-Pyknosis – nuclear shrinkage & increased basophilia.
-Karyorrhexis – pyknotic nucleus undergoes fragmentation.
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) andRead more
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:
See lessS. 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.