MI04 - Antibiotics and Resistance

OD1 MI lecture 4

Selective toxicity

Greater harm to microbes than to host - targets things like the bacterial ribosome or peptidoglycan

Theraputic index

Lowest dose to host to be effective:dose that is toxic to host

1000 mml toxic, 1 mml effective, so 1 mml is theraputic index

C. diff

Acquired enteric infection that causes diarrhea - opportunistic

Penecillins

Prevent synthesis of protein by blocking cross-linking

Beta-lactamases cleave penecillins

Methicillin and cephalosporin are penecillins that are resistant

What is augmentin made of?

Amoxicillin and clavulanic acid

Carbapenems

Affects gram - and gram +

Beta-lactamase inhibitor and peptidoglycan synthesis inhibitor

Protein Synthesis Inhibitors

Tetracyclines

Chloramphenicol

Aminoglycosides

Erythromycin

Clindamycin

Polypeptide Antibiotics

Polymixin b and bacitracin

Disrupts cell membranes

Rifampin

inhibits mRNA synthesis

DNA replicase inhibitor

ciprofloxacin

Metronidazole

specific for anaerobes

damages DNA

Trimethoprim

inhibits folic acid synthesis

often in bactrim

What kind of bacterial DNA carries resistances to antibiotics?

R plasmids

Name the 6 antibiotic resistance mechanisms

Impermeability

Binding-site alteration

Alternate pathway

Inactivation of antibiotic

Increase in sensitive sites

Production of excretion mechanisms like efflux pumps

Beta-lactamase antibiotics primarily inhibit what drug family?

Penecillins/beta-lactam antibiotics

Is S. aureus sensitive to penecillin?

Used to be more sensitive- now only 10-20% are

How does Staph. aureus resist penicillins? Methicillins?

Excretes beta-lactamase - breaks down the penicillin chains

Produces MecA which binds and inactivates methicillins and other cillins

What makes a good antibiotic target?

Wide theraputic index, good selective toxicity