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32 Cards in this Set
- Front
- Back
Bactericidal
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* loss of colony forming units (cfu)
* bactericidal antibiotics kill the bacteria - necessary in the absence of a functional immune system |
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Bacteriostatic
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* cessation of growth, but no death
* a bacteriostatic antibiotic will not kill the bacteria in an immunocompromised patient |
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Minimal Inhibitory Concentration (MIC)
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* minimal concentration of antibiotic that stops growth
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Minimal Bactericidal Concentration (MBC)
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* minimal concentration of bactericidal antibiotic needed to kill bacteria
* antibiotic concentration needed for it to be bactericidal |
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Selective Toxicity
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* relative toxicity to bacteria compared to host
* want an antibiotic that is selectively toxic for bacteria without being toxic to us |
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Antibiotic Antagonism
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* two antibiotics work worse together than by themselves
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Antibiotic Synergism
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* two antibiotics work better together than by themselves
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Broad Spectrum Antibiotics
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* antibiotics that kill most, if not all, bacteria
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Narrow Spectrum Antibiotics
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* kill only a few types of bacteria
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β-lactam Antibiotics: penicillins, ampicillin
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* bacteriocidal: but only kill growing bacteria
* blocks the synthesis of cell wall = lysis: if you are not growing, you are resistant. * bacteriolytic = causes bacteria to lyse * may develop resistance or allergic reactions * should not be used with a static antibiotic because a static would prevent the cell from growing = penicillin useless * synergistic: β-lactam and aminoglycosides |
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Penicillin Selection of Auxotrophs
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1) mutagenize culture of bacteria
2) grow culture in minimal medium that lacks leucine 3) add penicillin to lyse cells that are growing (non-mutants) 4) spin down and wash out the penicillin 5) grow again without leucine 6) add penicillin - whatever lives is your auxotroph |
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Aminoglycosides: gentamicin, streptomycin
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* protein synthesis inhibitor: target the 30S subunit, resulting in misreading of mRNA
* bactericidal antibiotic * don't penetrate mammalian membranes = intracellular membranes are resistant * synergistic: β-lactam and aminoglycosides |
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Chloramphenicol
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* protein synthesis inhibitor: attacks the 50S subunit of the ribosomes
* blocks protein synthesis * bacteriostatic antibiotic |
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Erythromycin
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* protein synthesis inhibitor: targets the 50S subunit
* is a macrolide: drug whose activity stems from having a macrolide ring in structure * bactericidal in some bugs and bacteriostatic in others |
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Tetracycline
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* protein synthesis inhibitor: targets the 30S subunit
* bacteriostatic antibiotic * antagonistic: tetracycline and β-lactam |
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Quinolones: naladixic acid, ciprofloxicin
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* inhibits DNA synthesis: binds to DNA gyrase
* bactericidal antibiotic * signle AA mutation in DNA gyrase leads to resistance |
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Rifampicin
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* inhibits RNA synthesis: binds to beta subunit of RNA polymerase
* bacteriostatic antibiotic |
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Mechanism of Antibiotic Resistance: Endogenous Resistance
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* gram negatives are resistant because they have a permeability barrier
* antibiotics cannot get past the outer membrane |
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Mechanism of Antibiotic Resistance: Multidrug Transport
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* the vast majority of bacteria have endogenous pumps that pump out antibiotics all the time
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Mechanism of Antibiotic Resistance: Spontaneous Resistance
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* spontaneous mutation that leads to resistance
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Mechanism of Antibiotic Resistance: Inactivating Enzymes
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* inactivating an antibiotic through an enzyme
Ex. β-lactamase cleaves the β-lactam ring of penicillins |
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Mechanism of Antibiotic Resistance: Target Alteration
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* change the target of the antibiotic
Ex. in erythromycin resistance, RNA on the ribosome changes so that erythromycin can't bind to it |
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Test for Antibiotic Sensitivity
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1) place little disks with different [ ]s of antibiotics on a lawn of bacteria
2) measure the distance of the zone of inhibition * zone = the area around the disk where all the bacteria have died 3) this defines susceptibility of the bacteria to the antibiotic |
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Natural Resistance - Outer Membrane (OM)
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* Due to their OM, gram negatives are more resistant to dyes, detergents, and antibiotics
* EDTA + detergent = lysis - the LPS contains magnesium that prevents repulsion of anions - adding EDTA chelates the magnesium - the LPS sheds off |
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Natural Resistance - Pore Size
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* some bacteria have small porins in their outer membrane
* antibiotics cannot get through these holes |
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Natural Resistance - Multidrug Efflux Pumps
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* no specificity: pump out so many molecules
* have a channel that goes across the membranes and a pump in the inner membrane * pump proteins out using ATP |
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Gram-Positive Susceptibility
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* gram positives are much more susceptible to antibiotics because they do not have the LPS
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Antibiotic Resistance: Spontaneous Acquired Resistance
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* single point mutations to drug resistance
* mutations affect virulence Ex. streptomycin mutant can be less virulent - ribosome affected so antibiotic couldn't bind - but bacteria unable to translate mRNA |
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Horizontal Gene Transfer
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* antibiotic resistance acquired by genetic transfer
* plasmids, phages, transposons may encode more than one antibiotic resistance - selection for one can lead to resistance to many antibiotics |
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Satellites
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1) transform a plasmid that encodes for penicillin resistance into your cells
2) plate them on agar plate that has penicillin 3) around each colony will be little dots (satellites) * the beta-lactamase is being released from the colonies * this lowers the [ ] of penicillin in the area around the colonies * they are not really resistant to penicillin |
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R factors
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* plasmids that confer resistance
* originate from soil isolates like streptomycetes |
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Bacteriocins
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* what bacteria make to kill their brothers and sisters
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