Gram + & Gram – Bacteria
THE BACTERIAL CELL WALL
Is a complex, semi-rigid structure responsible for the shape of the cell as well as the size
Surrounds the underlying, fragile plasma (cytoplasmic) membrane
Protects it and the interior of the cell from adverse changes in the outside environment
Major function is to prevent bacterial cells from rupturing Osmotic lysis
Distinct Gram + and Gram - traits
THE CELL WALL
Composed of macromolecular network called peptidoglycan Peptidoglycan consists of repeating disaccharide attached by polypeptides to form a lattice that surrounds and protects the entire cell
Disaccharide portion is made up of Alternating rows of 10-65 sugars to form a carbohydrate
“backbone” Monosaccharides called N-acetylglucosamine (NAG) and N-
acetylmuramic acid (NAM) Adjacent rows are linked by polypeptides
COMPOSITION & CHARACTERISTICS
Covalently attached to each NAM is a tetrapeptide chain
Tetrapeptide chains are linked by peptide cross-bridges
The result is a 3-D meshwork held together by covalent bonds
PEPTIDOGLYCAN STRUCTURE
Tetrapeptide chain
Peptide bridgePeptidoglycan
Tetrapeptide chain
Many layers of peptidoglycan Thick layer (rigid structure) of peptidoglycan
Thicker than Gram – cell wall
Cell wall contains teichoic acids Help in:
Attachment to surfaces Provides rigidity Helps in cell growth regulation Two types
Lipoteichoic acid Wall teichoic acid
Produce Exotoxins
Stains Purple during Gram Stain Lab test Example:
Streptococcus pyogenes (strep throat)
GRAM POSITIVE (+) CELL WALL
GRAM + CELL WALL
What do the green spheres represent?What do the blue spheres represent?
Analyze the cell wall of a Gram + bacteria
What part would be attacked by antibiotics and why? What would this do to the cell. Explain
http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/prostruct/penres_fl .html
GRAM (+) AND ANTIBIOTICS
One or very few layers of peptidoglycan Thin layer (not as thick as gram +)
Does NOT contain teichoic acidsHas an outer membrane outside the peptidoglycan
layer Consists of lipopolysaccharide (LPS), lipoproteins,
phospholipids
GRAM NEGATIVE (-) CELL WALL
The outer membrane has several specialized functions
Its strong negative charge is an important factor in evading phagocytosis
Provides a barrier to certain antibiotics (for example penicillin), digestive enzymes, detergents
Permeability of outer membrane due to porins which allow passage of large molecules across the outer membrane
LPS (known as endotoxin) helps bacteria secrete toxins Endotoxins and Exotoxins
Example: Escherichia coli (food poisoning)
Stains Pink in Gram Stain Lab test
GRAM (–) CELL WALL
Analyze the Gram – bacterial structure
Why would Gram – bacteria be more resistant to antibiotics?
GRAM (-) AND ANTIBIOTICS
Diff erences between Gram (+) and Gram (-) Bacteria: Structural and functional differences between Gram-
positive and Gram-negative cell walls can be used for identification and treatment of bacterial infections.
Basis for Gram stain (gram-positive = purple; gram-negative = pink)
GRAM STAIN
GRAM STAIN LAB TEST