Term
| What is selective toxicity? |
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Definition
= selectivity - better able to kill bacteria over host cells.
Higher = more selectively toxic against microbe. |
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Term
| What is the MoA of penicillins? |
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Definition
| Cell wall inhibitors - eukaryotes have no cell wall! |
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Term
| What is the MoA of erythromycin and tetracycline? |
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Definition
| Inhibit protein synthesis |
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Term
| What is the MoA of amphotericinB? |
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Definition
| Inhibits cell membrane function. Both eukaryotes and prokaryotes have cell membranes = low selectivity |
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Term
| What is therapeutic ratio? |
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Definition
AKA therapeutic index - ratio of toxic dose to effective dose: Toxic/Therapeutic.
**Want toxic dose to be high, and therapeutic dose to be low. IF they are close to each other, we get a narrow therapeutic index. |
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Term
| How does TI relate to selectivity? |
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Definition
- Direct relationship - goes in the same direction (positive or negative)
- Indirect - opposite directions |
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Term
| What antibiotics affect protein synthesis? |
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Definition
- Chloramphenicol - inhibits 50S
- Erythromycin - Inhibits 50S
- Aminoglycosides - Inhibits 30S
- Tetracycline - inhibits aminoacyl, stopping tRNA from binding to ribosome |
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Term
| What is the difference between a 'static' and a 'cidal' antibiotic? |
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Definition
- Static - Inhibits replication, relying on host to kill the cells
- Cidal - directly kills microbes. For severe infections and the immunocompromised. |
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Term
| How does the growth curve affect antibiotics? |
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Definition
| The log/exponential phase is when organisms multiply, and when antibiotics should be taken. Since we don't know phase of growth, always take antibiotic for the prescribed time |
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Term
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Definition
- MIC - Minimum amount required to stop growth of organism. Target = 10*MIC
- MBC - minimum amount to kill organism |
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Term
| How does protein binding affect antibiotics? |
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Definition
| Inactivates them, but if the 1% that is not reaches 10*MIC, it is effective. |
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Term
| What is a superinfection? |
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Definition
| Overgrowth, usually by yeast, seen with broad spectrum antibiotics - disturbs normal flora. |
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Term
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Definition
| The MIC needed to determine susceptibility. Either susceptible, intermediate, resistant |
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Term
| What is intracellular killing? |
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Definition
Organisms hide inside macrophages - Mycobacterium tuberculosis and Legionella pneumophila
**FQNs can kill the organisms |
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Term
| What is the post antibiotic effect? |
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Definition
| Suppression of an organism after exposure and removal of an antibiotic. Seen in antibiotics that inhibit DNA or protein synthesis - against gram(-) |
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Term
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Definition
| Microbes without cell walls - Mycoplasma pneumoniae. Penicillins will not work. |
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Term
| What are the different spectrums of an antibiotic? |
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Definition
- Narrow - Works on either gram(+) or gram(-)
- Intermediate - gram(+) or gram (-) with some extended activity. 1st gen cephalosporins
- Broad - gram(+) and gram(-) |
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Term
| What is the plate diffusion test? |
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Definition
Zone of inhibition is directly proportional to log of antibiotic concentration.
**Less contamination, quick, easy |
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Term
| What is the serial dilution test? |
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Definition
Series of tubes with 2x conc. of antibiotics - determines the MIC and can be cultured to determine MBC
** determine MIC, very sensitive, |
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Term
| How is serial dilution a good test? |
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Definition
| Can test several organisms by streak, rarely contaminated, quick, can determine MIC |
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Term
| What are the 3 mechanisms of drug resistance? |
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Definition
- Mutation - change in gene sequence. Not from antibiotics.
- Recombination - usually conjugation, takes up long pieces of chromosome.
- Acquisition of plasmids - episomes can attach to chromosomes. Often code for resistance. |
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Term
| What are the components of a plasmid? |
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Definition
- Transfer unit - contains a gene, RTF, that directs transfer during conjugation
- R-determinant - contains genetic determinants. Can exist without transfer unit |
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Term
| What is the biochemical basis of resistance? |
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Definition
- Decr permeability - most common mechanism, decreased uptake/incr efflux
- Enzyme inactivation
- Alteration at target site - competing substances (PABA and sulfa) or drug receptor (Reductase instead of synthetase in sulfa)
- Decreased receptor affinity for drug - ribosome modified, PBPs larger, DNA-gyrase (FQNs) |
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Term
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Definition
Griseofulvin
Metronidazole
FQNs |
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Term
| What agents inhibit protein synthesis? |
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Definition
- 50s - Chloramphenicol, macrolides
- 30S - Tetracyclines - static
- 30S - Aminoglycosides - Cidal |
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Term
| What agents affect cell wall synthesis? |
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Definition
Cephalosporins
Penicillins
Vancomycin |
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Term
| What agents affect the cell membrane? |
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Definition
Polymyxin
AmphotericinB
Nystatin
Ketoconazole |
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Term
| What agents block metabolic steps in microorganisms? |
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Definition
| - Sulfa - inhibits PABA so the bug does not get folic acid |
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Term
| What is an ideal antibiotic? |
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Definition
- Broad spectrum and cidal
- Low toxic
- Stable, water soluble, acid stable |
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Term
| What are the rules for antibiotic combination? |
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Definition
- Static + Static = additive
- Cidal + static = Antagonistic
- Cidal + Cidal = synergism |
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