Term
| Spectrum of antimicrobial activity |
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Definition
| the range of microbes affected by an antimicrobial |
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Term
| Narrow spectrum antibiotics |
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Definition
effective only against a limited variety of microbes
Ex: Bacitracin (G+) |
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Term
| Broad Spectrum antibiotics |
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Definition
effective against wide variety of G+ and G- bacteria
Ex: 1. Tetracyclines (G+, G-, mycoplasmas, mycobacteria)
2. Trimethoprim (G+, G-, against DNA and nucleic acid synthesis) |
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Term
| Antibiotics kill sensitive bacteria and become favorable for..... |
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Definition
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Term
| Action of antimicrobial drugs: |
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Definition
1. inhibition of cell wall synthesis
2. inhibition of protein synthesis
3. Injury to the plasma membrane
4. Inhibition of nucleic acid synthesis
5. Inhibition of enzymatic activity |
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Term
| 1. Inhibition of cell wall synthesis: (narrow) |
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Definition
-inhibit transpeptidation enzymes involved in the cross-linking of the polysaccharide chains of the bacterial cell wall peptidoglycan
-cell wall synthesizes at log
- drugs are effective in rapidly growing bacteria
-cell wall prevents from lyses
EX: penicillins, vancomycin, bacitracin, cephalosporins |
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Term
| 2. Inhibition of protein synthesis: (broad) |
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Definition
-translation, no transcription
- the process of protein synthesis is same in prokaryotic and eukaryotic cells
-The difference in ribosomal structure accounts for the selective toxicity of antibiotics that affect protein synthesis.
EX: Chloramphenicol, tetracyclines, erythromycin, streptomycin |
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Term
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Definition
| prevents peptide bond formation between growing polypeptide chain |
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Term
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Definition
| interfere with protein synthesis by preventing the attachment of the amino-acid-carrying tRNA (anticodon) to mRNA (codon)-prevents the bonding |
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Term
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Definition
| jams the ribosome on mRNA, binds to 50S and prevents traslocation |
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Term
| ***Gentamycin and streptomycin |
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Definition
| appear to act by changing the shape of 30S subunit of the ribosome, causing misreading of the genetic code |
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Term
| 3. Injury to the plasma membrane: (broad) |
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Definition
the cytoplasmic membrane is selectively permeable structure that controls the transport of many metabolites into and out of the cell. This damage to this structure hampers or destroys its ability to prevent a number of necessary biosynthetic functions (synthesis of ATP or cellular respiration) from taking place in the membrane
EX: polymyxin-B, nystatin, amphotericin-B |
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Term
| *Polymyxin-B (antibacterial) |
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Definition
| attaches to phospholipids of membrane and increase permeability |
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Term
| ***Amphotericin-B and nyastatin (antifungal) |
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Definition
combine with sterols which are not found in bacterial membrane but are present in animal membranes and can be toxic to the host
Fungi--Eukaryote
Animal--" " |
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Term
| 4. Inhibition of nucleic acid synthesis: (broad)-->Avoid |
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Definition
-transcription and translation
-any antibiotic that specifically reacts with DNA to prevent its replication or transcription will inhibit cell growth and division.
-use is limited d/t lack of selectivity
EX: idoxuridine, rifamycin, nalidixic acid, trimethoprim
***trimethoprim-stop synthesis of nucleic acid |
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Term
| 5. Inhibition of enzymatic activity: |
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Definition
-transcription and translations
-an antimetabolite is a substance that prevents a cell from carrying out a metabolic reaction
-(PABA)
EX:sulfonamides
vidarabine (purine analog) A, G
idoxuridine (pyrimidine analog) T, C
-Most useful in tx viral diseases b/c viruses incorporate analogs more rapidly than cells and are more severely damaged. |
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Term
| ***Bacteria become drug resistant in what ways? |
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Definition
1. alternation of receptors to which antimicrobial agents bind
2. a mutation that allowas the organism to bypass the sensitive step inhibited by antibiotic
3. a mutation that changes the nature of proteins in the cell membrane so an antimicrobial agent no longer crosses the membrane, usually acquired by R-factor (R-plasmid)
4. Development of enzymes that can destroy or inactivate antimicrobial agents (most common) acquired by plasmid.
ex: one enzyme of this type is beta-lactamase. Several beta-lactamases exist in various bacteria; they are capable of breaking the beta-lactam ring in penicillins and cephalosporins |
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Term
| The origin of drug resistance: |
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Definition
1. spontaneous mutations (1 per million to 1 per billion
2. R-factors, a single plasmid may carry genes for resistance to several drugs. Plasmids may be transferred to other cells through conjugation, transduction and transformation
3. Extensive drug treatment destroys normal flora and leads to superinfection. Ex:Clostridium dificile |
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Term
| Synergistic effect (1+1=>2) |
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Definition
enhance each others effect
Ex: Penicillin and streptomycin |
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Term
| Antagonistic effect (1+1=<2) |
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Definition
undesirable effect,neutralize
Ex: Penicillin and tetracycline |
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Term
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Definition
don't enhance nore neutralize
Ex: trimethoprim and tetracycline |
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Term
| Why may combination of drugs be used? |
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Definition
1. to minimize the development of resistant strains
2. to achieve synergistic effect
3. to provide therapy prior to diagnosis
4. to use small dosage of each drug to lessen toxicity |
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Term
| Mode of action of penicillin? |
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Definition
| eliminate the enzyme that sugar and peptidoglycan, cell wall prevents from lyses |
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Term
Penicillin resistance
Cephalosporin resistance |
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Definition
| beta- lactamase exist in various bacteria; capable of breaking the beta-lactam ring |
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Term
| Antibiotics that interfere with protein synthesis? |
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Definition
| Chloramphenicol, tetracyclines, erythromycin, streptomycin |
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