8_26 Bacterial Cell Walls.pptx

Bacterial Cell Walls  Why the fuss? Cell Wall used for Classification Often Determines Antibiotic sensitivity Gives Shape Contains Toxins Related to Virulence  Functional Types of Cell Walls I. Gram positive I. Simple wall II. Gram Negative I. Complex mul...

Bacterial Cell Walls  Why the fuss? Cell Wall used for Classification Often Determines Antibiotic sensitivity Gives Shape Contains Toxins Related to Virulence  Functional Types of Cell Walls I. Gram positive I. Simple wall II. Gram Negative I. Complex multi-layered wall III. Bacteria Lacking Cell Walls IV. Bacterial with chemically unique cell walls Typical Gram Stain Figure 3.17 Gram positive Gram negative Fig 4.16  Peptidoglycan Structural Polysaccharide Glycan chain of repeating subunits – N-acetylglucosamine (NAG) – N-acetylmuramic acid (NAM) Cross-linked by tetrapeptide chains – Composition of cross-links often differs for each species of bacteria – Gram negative bacteria often lack the peptide interbridge  Cell Wall Rigidity of cell wall is due to peptidoglycan (PTG) – Compound found only in bacteria Basic structure of peptidoglycan – Alternating series of two subunits N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) – Joined subunits form glycan chain Glycan chains held together by string of amino acids – Tetrapeptide chain Figure 3.21 Gram + Cell Wall  Lipotechoic Acids Considered virulence factor Released from killed cells – Similar to endotoxin of Gram – Bind immune receptors – Stimulated inflammation – Cytokine cascades – Complement activation – Oxidative burst from macrophages Gram - Cell Wall  Lipopolysaccharide Layer Prevalent in many Gram – Bacteria LPS – Lipid A – sugar modified lipid Characteristic of different groups Often an endotoxin – Core polysaccharides – sugar backbone – O-side chain – important in eliciting the immune response in host Used to ID specific strains of bacteria (O157H7) LPS Creates permeability barrier  Summarize Make a two lists comparing the two major types of cell walls How can knowledge of cell wall help you? What may be consequences of bacteriolysis in the body?  Next Time Cell division and growth