Antibiotics Lectures Flashcards
What is a bacteriostatic agent?
Does not kill targeted microbe, just inhibits growth
When log viable count is taken it stays steady, does not decrease
Reversible, when removed colonies begin to grow again
Act as competitive inhibitors that mimic metabolites
May interfere with action of bacteriocidal drugs
What are the tenets of selective toxicity?
Absence of the Target (host does not posess the drug’s target)
Permeability differences (some drugs can get into cells and some cant; drug must be catered toward intracellular v. extracellular organism)
Structural Differences (the target may have similar machinery with subtle differences that allow for specific targeting)
What drugs target metabolic pathways?
Sulfa Drugs target metabolic pathways
They mimic PABA to inhibit dihydropteroate synthase
Prevents the synthesis of folic acid
PAS which acts against TB effects a slightly different version of the enzyme
Human cells are safe because we do not synthesize our own folic acid
Can act in unison with trimethoprim
What drugs inhibit Nucleic Acid Synthesis?
Rifampin and Rifabutin
Bind permanently to RNA Poly specific to bacteria
Prevents initiation of transcription; no effect of transcription in progress
Bactericidal
Mitochondrial DNA unaffected because membrane impermeable
What drugs inhibit DNA replication?
Quinolones and Metronidazole
Quinolones are broad spectrum and bactericidal
Quinolones bind DNA Gyrase or Topoisomerase IV and cause DNA strand breakage
Metronidazole is used for anaerobic infections; when active it causes secondary DNA mutations
Metronidazole starts as a pro-drug and is converted by bacteria to active form
Naladixic acid is used only for UTIs
What drugs affect bacterial membranes?
Polymixins (Colistin)
Insert themselves into bacterial membranes near LPS and phosphoethanolamine
Host cells lack both
Disrupt membrane causing cell death through leaks
Some gram negative bacteria have LPS that makes them impermeable conveying resistance
Explain the mechanism of synergism between sulfa drugs and trimethoprim
Sulfa drugs are metabolite mimics for one enzyme
trimethoprim does the same for an enzyme further down the chain eliminating the bacterias ability to use already stored substrate
What are common B-lactams and how do they work?
Penicillins, Ampicillin, Amoxicillin
Mimic D-ala dimers present in pentapeptides on MurNac
Irreversibly bind transpeptidase and carboxypeptidase
Prevent formation of linkages between cell wall structures
Cells automatically lyse because they outgrow their cell wall
What drugs prevent transglycosylation? How do they work?
Vancomycin and Bacitracin (Glycopeptides)
Bind D-ala dimers and cause steric hindrance preventing new peptidoglycans from binding
Cells automatically lyse because they outgrow their cell wall
Natural Penicillins
Penicillin G/V
Kills Cocci, G+ Rods, Spirochetes
Bactericidal
Binds transpeptidase to inhibit cell wall synthesis
Aminopenicillins
Ampicillin, Amoxicillin
Kills Cocci, G+ Rods, Spirochetes, E. Coli, Salmonella, Shigella
Bactericidal
Binds transpeptidase and prevents cell wall synthesis
Penicillinase Resistant Penicillins
Nafcillin, Oxacillin, Dicloxacillin
Kills S. Aureus
Bactericidal
Binds PBPs to prevent cell wall synthesis
Antipseudomonal
Ticarcillin, Piperacillin
Kills P auriginosa
Bactericidal
Binds PBP to prevent cell wall synthesis
B-lactamase inhibitors
Clavulanic Acid, Sulbactam, Tazobactam
Given in conjuction with penicillin
Bactericidal
Prevents b-lactamase from breaking down penicillins allowing them to bind PBP and inhibit cell wall synthesis
Cephalosporins
Name starts with “Cef”
Kill Gram positive cocci
Bactericidal
Bind PBPs and prevent cell wall synthesis
