Bacteria 3 Flashcards
Gram Stain reaction
Make film, flood with crystal violent, all cells take up the dye, flood with Lugol’s iodine, all cells appear blue-black, decolourise with acetone. Gram positive cells retain dye complex, gram negative cells are decolourised, counter stain with red dye. Gram positive cells appear blue-black and gram negative cells appear red
Lugols iodine
Fixes crystal violent to cell wall
Example of counter stain
Safrinin
Gram + cell envelope
Plasma membrane, periplasmic space, peptidoglycan (thick layer crystal violet sticks to), lipoteichoic acid, teichoic acid
Proteins
Transpeptidase (penicillin binding protein) helps cross link peptidoglycan side chains (transpeptidation)
Penicillin based antibiotics
They target penicillin binding proteins to stop further cross linking making bacteria less resistant to osmotic pressure meaning cell walls more likely to lysis
Gram negative envelope
Contains less thick peptidoglycan and lipopolysaccharide
White cell exotoxins
Leukocydin
How the exotoxin works 1st
Two components of Panton-valentine leukocidin secreted from S. aureus. Assemble into a pore-forming heptamer on polymorphonuclear white cell (PMN) membranes. These are known as pus cells or leukocytes.
How the exotoxin works
High conc of pvl toxin in cell membrane of polymorphs releases enzymes from cytoplasm. The lysed PMN = inflammatory response eventually tissue necrosis
Endotoxins
Produced by gram negatives
LPS
Lipopolysaccharide
Gram negative endotoxin
Outer membrane, peptidoglycan, inner membrane, porin, membrane protein, periplasmic space, phospholipid, lipid A, LPS (core and O-polysaccharide)
Basic structure
O antigen, Core, Lipid A
Endotoxin
Endotoxin = lipopolysaccharide = prevotella intermedia (associated with periodontal disease)
