Structure of Bacterial Cells

Structure of Bacterial Cells
Morphology of bacterial cells:
• Shape : it is determined by the bacterial rigid cell wall, the bacteria are classified according to their shapes into four basic groups:
Cocci: are spherical shape.
Bacilli : are rods shape.
Spirochetes : are spiral–shaped.
Pleomorphic: appear in many shapes.
• Size: the size of bacteria ranged from 0.2-5 micrometer (?m).
• Arrangement of bacteria: Certain bacteria are arranged in single cell or in pairs, some in chains, and others in groups.

Bacterial Structure:
1- Cell wall: is the rigid outermost layer of all bacteria (except mycoplasma species, have only cell membrane without cell wall) located outside the cell membrane. The principal structural component of it is peptidoglycan which provides the structural support and maintain the characteristic shape of the bacterial cell.
The differences in the structure, chemical composition and thickness of the cell wall divide bacteria into two main groups according to the reaction of Gram stain with components of cell wall; Gram positive and Gram negative bacteria.
• Peptidoglycan is much thicker, multiple layers in Gram positive bacteria than in Gram negative bacteria (less and thin layers); also has fibers of teichoic acid protrude outside the peptidoglycan that are absent in Gram negative bacteria.
This thick wall makes gram positive bacteria more susceptible to antibiotic that inhibit cell wall synthesis (such as penicillins).
• Cell wall of Gram negative bacteria have a complex outer membrane which is composed of lipopolysaccharide (LPS) and lipoproteins. The LPS is act as endotoxine (LPS not