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