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Escherichia coli
Escherichia coli
Gram Negativebacilli
Description
E. coli is a gram-negative, facultative anaerobic bacterium commonly found in the lower intestine of warm-blooded organisms. Most strains are harmless and part of normal gut flora, but some can cause serious food poisoning.
Membrane Composition
Key Properties
Peptidoglycan:2-7 nm (thin)
Lipopolysaccharide:Present
Teichoic Acid:Absent
Outer Membrane:Present
Membrane Components
- •Inner membrane (phospholipids)
- •Thin peptidoglycan layer
- •Outer membrane with LPS
- •Porins
Understanding Gram Classification
Gram-negative bacteria do not retain the crystal violet stain due to their thin peptidoglycan layer (2-7 nm) and outer membrane structure. They appear pink/red after counterstaining with safranin.
The cell envelope has a complex structure: an inner membrane, a thin peptidoglycan layer in the periplasmic space, and an outer membrane containing lipopolysaccharides (LPS). This outer membrane provides extra protection against antibiotics and immune responses.