Micro Lecture CH20
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Name the microbes that produce most antibiotics.
More than half of our antibiotics are produced by species of Streptomyces, filamentous bacteria that commonly inhabit soil (554)
Describe the problems of chemotherapy for viral, fungal, protozoan, and helminthic infections.
At cellular level, these organisms resemble the human cell much more closely than a bacterial cell does. By treating these pathogens, we kill our own normal microbiota.
Define the following terms: spectrum of activity, broad-spectrum drugs
spectrum of activity-range of different microbial types drugs affect
broad-spectrum drugs-antibiotics that affect a broad range of gram pos or gram neg bacteria
Identify five modes of action of antimicrobial drugs.
- Inhibiting cell wall synthesis
- Inhibiting Protein synthesis
- Injuring the plasma membrane
- Inhibiting nucleic acid synthesis
- Inhibiting the synthesis of Essential Metabolites
Explain why the drugs described in this section are specific for bacteria.
- because bacteria does not share the same microbial structures or functions as us eukaryotes.
- we have no cell wall; only a plasma membrane
- even this membrane differs in composition from the plasma membrane of prokaryotic cells. for this reason, the mirobial cell wall is an attractive target for the action of antibiotics (559)
List the advantages of each of the following over penicillin: semisynthetic penicillins, cephalosporins, and vancomycin.
semisyntheic penicillins-scientists develop these penicillins in either of two ways. first they can interrupt synthesis of the molecule by Penicillium and obtain only the common penicillin nucleu for use. second, they can remove the side chains from the completed natural molecules and then chemically add other side chains that make them more resistant to penicillinase, or the scientists can give them an extended spectrum
cephalosporins-these inhibit cell wall synthesis in essentially the same way as do penicillins. they have more extended specturm of activity
vancomycin-although it has a vary narrow spectrum of activity it has been extremely important in addressing the problem of MRSA (563)
Describe how each of the following inhibits protein synthesis: aminoglycosides, tetracyclines, chloramphenicol, macrolides.
aminoglycosides-by changing the shape of the 30S portion of the 70S prokaryotic ribosome. This interference causes the genetic code of the mRNA to be read incorrectly
tetracyclines-interferes with the attachment of the tRNA carrying the amino acids to the ribosomes at the 30S portion of the 70S ribosome, preventing the addition of amino acids to the growing polypeptide chain
chloramphenicol-inhibits the formation of peptide bonds in the growing polypeptide chain by reacting with the 50S portion of the 70S prokaryotic ribosome. Because of its simple structure, it is less expensive for the pharmaceutical industry to synthesize it chemically than to isolate it from Streptomyces
macrolides-by blocking the tunnel
Compare the mode of action of polymyxin B, bacitracin, and neomycin.
bacitracin-inhibits the synthesis of cell walls at an earlier stage then penicillins and cephalosporins
Describe how rifamycins and quinolones kill bacteria.
Describe how sulfa drugs inhibit microbial growth.
Explain the modes of action of currently used antifungal drugs.
Explain the modes of action of currently used antiviral drugs.
Explain the modes of action of currently used antiprotozoan and antihelminthic drugs.
Describe two tests for microbial susceptibility to chemotherapeutic agents.
Describe the mechanisms of drug resistance.
Compare and contrast synergism and antagonism
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