Cell Exteriors and Antibiotics

E.coli

• Pili or frimbrimae for attachment 

  • Binds to intestinal microvilli

Bad E.coli video

• O157:H7 = serotype 

• LPS structure

• Added DNA = pathogenic islands = operons to allow infection

• TTSS = type III secretion system

  • Tube of proteins help bacteria get rid of things

Operons

• Several genes in the same process controlled by 1 promoter = on/off switch 

• Repressor = blocks transcription = no gene expression

  • Removed by outside chemical signals

petri/agar 

• Diff cell exterior = different colony formation 

• Some lack capsule = lack active flagella 

• capsule/flagella = no single colonies

Structure of peptidoglycan

• NAG-NAM sugars with peptide bonds/bridge = strong/flexible

Repair of peptidoglycan

• Autolysin

  • Break cell wall allowing new to come in and break chain

• Bactoprenol

  • Binds to monomer and carries it out

Lysoensyme-insensitive 

• Enzyme hydrolysis (breaks) glycositic bond between NAG/NAM

Beta-lactams vs glycopeptides

•  Beta-lactams

  • target and inhibit the D,D-transpeptidase component of penicillin-binding proteins (PBPs)

• Glycopeptides

  • bind to the D-Ala-D-Ala terminus of peptidoglycan precursors, blocking their assembly

Gram +

• Thick cell wall

• No LPS layer

• Typoic acids

  • Polymers of glycerol or ribitol joined via phosphate

  • Attach to sugars (d-alanine)

Gram -

• Think cell wall (peptigoglycan layers)

• LPS layer 

  • Fatty acids

  • More hydrophobic = harder for polar molecules 

• O-polysaccharide

  • Diff antibodies rxn with different strains 

• Porin proteins 

• DAP-d-Ala bond is formed through the cross-linking of the peptidoglycan layer

attacks the terminal d-Ala of an adjacent peptide stem

LPS structure

• O-specific polysaccharide + core polysaccharide + lipid A

• Lipid A

  • Fatty acids 

  • Endotoxin = toxic shock (increase inflammation, decrease BP)

Diamino acids

• DAP

• Have R groups

  • H2N - CH - COOH

• Lysine = no COOH (H2N - CH - H)

PBP

• Penicillin binding protein

• Makes peptide bonds

• Bind and block activity = lyses if cell growing and making new cell 

• PBP2 = mutant form of PBP

  • MRSA

  • Build cell walls 

  • Penicillin + cephalosporins (betalactins)

  • Resistant to penicillin

    • Stop binding

    • B-lactamase = breaks betalactome antibodies

PBP inhibitors 

• Bacitracin

• B-lactam drugs

• Vancomycin

Bacitracin

• Blocks secretion of NAG/NAM from cytoplasm

  • Limit movement of monomer = attack cell wall metabolism 

• Inhibit PBP

b-lactam drugs

• Interfere with the formation of peptide side chains 

  • Formation and repair

• Inhibit PBPs

Vancomycin

• Binds to ala-ala (monomers)

• PBP can’t use monomer to make new cell walls

• Susceptible cell

  • Can’ bind to monomers and make new CW

  • Resistance - intermediate

    • Makes excess of peptidoglycan

    • CAN still make new CW

Types (least to most resistant)

• VISSA (susceptible cell)

• VISA

• VSRA (mutation of vancomycin = ability to bind ala-ala)