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32 Cards in this Set

  • Front
  • Back
* loss of colony forming units (cfu)

* bactericidal antibiotics kill the bacteria
- necessary in the absence of a functional immune system
* cessation of growth, but no death

* a bacteriostatic antibiotic will not kill the bacteria in an immunocompromised patient
Minimal Inhibitory Concentration (MIC)
* minimal concentration of antibiotic that stops growth
Minimal Bactericidal Concentration (MBC)
* minimal concentration of bactericidal antibiotic needed to kill bacteria

* antibiotic concentration needed for it to be bactericidal
Selective Toxicity
* relative toxicity to bacteria compared to host

* want an antibiotic that is selectively toxic for bacteria without being toxic to us
Antibiotic Antagonism
* two antibiotics work worse together than by themselves
Antibiotic Synergism
* two antibiotics work better together than by themselves
Broad Spectrum Antibiotics
* antibiotics that kill most, if not all, bacteria
Narrow Spectrum Antibiotics
* kill only a few types of bacteria
β-lactam Antibiotics: penicillins, ampicillin
* 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
Penicillin Selection of Auxotrophs
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
Aminoglycosides: gentamicin, streptomycin
* 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
* protein synthesis inhibitor: attacks the 50S subunit of the ribosomes

* blocks protein synthesis

* bacteriostatic antibiotic
* 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
* protein synthesis inhibitor: targets the 30S subunit

* bacteriostatic antibiotic

* antagonistic: tetracycline and β-lactam
Quinolones: naladixic acid, ciprofloxicin
* inhibits DNA synthesis: binds to DNA gyrase

* bactericidal antibiotic

* signle AA mutation in DNA gyrase leads to resistance
* inhibits RNA synthesis: binds to beta subunit of RNA polymerase

* bacteriostatic antibiotic
Mechanism of Antibiotic Resistance: Endogenous Resistance
* gram negatives are resistant because they have a permeability barrier

* antibiotics cannot get past the outer membrane
Mechanism of Antibiotic Resistance: Multidrug Transport
* the vast majority of bacteria have endogenous pumps that pump out antibiotics all the time
Mechanism of Antibiotic Resistance: Spontaneous Resistance
* spontaneous mutation that leads to resistance
Mechanism of Antibiotic Resistance: Inactivating Enzymes
* inactivating an antibiotic through an enzyme

Ex. β-lactamase cleaves the β-lactam ring of penicillins
Mechanism of Antibiotic Resistance: Target Alteration
* change the target of the antibiotic

Ex. in erythromycin resistance, RNA on the ribosome changes so that erythromycin can't bind to it
Test for Antibiotic Sensitivity
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
Natural Resistance - Outer Membrane (OM)
* 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
Natural Resistance - Pore Size
* some bacteria have small porins in their outer membrane

* antibiotics cannot get through these holes
Natural Resistance - Multidrug Efflux Pumps
* 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
Gram-Positive Susceptibility
* gram positives are much more susceptible to antibiotics because they do not have the LPS
Antibiotic Resistance: Spontaneous Acquired Resistance
* 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
Horizontal Gene Transfer
* 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
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
R factors
* plasmids that confer resistance

* originate from soil isolates like streptomycetes
* what bacteria make to kill their brothers and sisters