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Bacterial Endotoxin - Textbook of Bacteriology
b. Daptomycin disrupts the bacterial cytoplasmic membrane function by apparently binding to the membrane and causing rapid depolarization. This results on a loss of membrane potential and leads to inhibition of protein, DNA and RNA synthesis, resulting in bacterial cell death.
Exotoxinsare usually secreted by bacteria and act at a site removed frombacterial growth. However, in some cases, exotoxins are only releasedbylysis of the bacterial cell. Exotoxins are usually proteins, minimallypolypeptides, that act enzymatically or through direct action with hostcells and stimulate a variety of host responses. Most exotoxins act attissue sites remote from the original point of bacterial invasionor growth. However, some bacterial exotoxins act at the site ofpathogen colonizationand may play a role in invasion.
Inhibitors of Bacterial Protein Synthesis | Basicmedical Key
Bacterial protein toxins are the most powerful human poisons knownandretain high activity at very high dilutions. The lethality of the mostpotent bacterial exotoxins is compared to the lethality of strychnine,snake venom, and endotoxin in Table 1 below.
Endotoxins are cell-associated substances that are structuralcomponents of bacteria. Most endotoxins are located in the cellenvelope. In the context of this article, endotoxin refers specificallyto the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) located inthe outer membrane of Gram-negative bacteria. Although structuralcomponents of cells, soluble endotoxinsmay be released from growing bacteria or from cells that are lysedas a result of effective host defense mechanisms or by the activitiesof certain antibiotics. Endotoxins generally act in the vicinity ofbacterial growth or presence.
Protein synthesis inhibitor antibiotics - SlideShare
Interference with this process results in the formation of a weak cell wall and osmotic lysis of the bacterium. Agents that inhibit peptidoglycan synthesis include the penicillins (penicillin G, methicillin, oxacillin, ampicillin, amoxicillin, ticarcillin, etc.), the cephalosporins (cephalothin, cefazolin, cefoxitin, cefotaxime, cefaclor, cefoperazone, cefixime, ceftriaxone, cefuroxime, etc.), the carbapenems (imipenem, metropenem), the monobactems (aztreonem), and the carbacephems (loracarbef). Penicillins, monobactams, carbapenems, and cephalosporins are known chemically as beta-lactam antibiotics because they all share a molecular structure called a beta-lactam ring (see Fig. 5). The glycopeptides (vancomycin, teichoplanin) and lipopeptides (daptomycin) also inhibit peptidoglycan synthesis.
Bacterial protein toxins are strongly antigenic., specificantibody neutralizes the toxicity of these bacterialexotoxins (antitoxin). However, specific antitoxin may not fully inhibit theiractivity. This suggests that the antigenic determinant of thetoxin may be distinct from the active portion of theproteinmolecule. The degree of neutralization of the active site may dependon the distance from the antigenic site on the molecule. However, sincethe toxin is fully neutralized , this suggests that other hostfactorsmust play a role in toxin neutralization in nature.
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01/10/2016 · Bacterial Protein Synthesis ..
Penicillins, cephalosporins, as well as other beta-lactam antibiotics, bind to the transpeptidase enzymes (also called penicillin-binding proteins) responsible for reforming the peptide cross-links between rows and layers of peptidoglycan of the cell wall as new peptidoglycan monomers are added during bacterial cell growth. This binding blocks the transpeptidase enzymes from cross-linking the sugar chains and results in a weak cell wall. In addition, these antibiotics appear to interfere with the bacterial controls that keep autolysins in check, with resulting degradation of the peptidoglycan and osmotic lysis of the bacterium (see Fig. 6).
faulty protein synthesis (see Common Antibiotics ..
During normal bacterial growth, bacterial enzymes called autolysins put breaks in the peptidoglycan in order to allow for insertion of new peptidoglycan monomers consisting of NAG, NAM, and a pentapeptide. As new monomers are linked to the existing rows of peptidoglycan during cell wall synthesis, transpeptidase enzymes (also called penicillin-binding proteins) form a peptide bridge that cross-links the peptides coming off of each NAM. These links connect each row of sugars with its adjacent rows and each layer of peptidoglycan with its adjacent layers. This is what gives peptidoglycan its strength.
Many antibiotics inhibit bacterial protein synthesis
At a chemical level, there are two main types ofbacterial toxins,lipopolysaccharides,which are associated with the cell wall of Gram-negative bacteria, andproteins,which are released from bacterial cells and may act at tissue sitesremovedfrom the site of bacterial growth. The cell-associated toxinsare referred to as endotoxinsand the extracellulardiffusible toxins are referred to as exotoxins.
Inhibitors of bacterial protein synthesis - Oxford …
Great variation occurs in the composition of the sugars in the Osidechain between species and even strains of Gram-negative bacteria. Atleast20 different sugars are known to occur and many of these sugars arecharacteristicallyunique dideoxyhexoses, which occur in nature only in Gram-negative cellwalls. Variations in sugar content of the O polysaccharide contributetothe wide variety of antigenic types of and and presumably other strains of Gram-negative species. Particularsugarsin the structure, especially the terminal ones, confer immunologicalspecificityof the O antigen, in addition to "smoothness" (colony morphology) ofthestrain. Loss of the O specific region by mutation results in the strainbecoming a "rough" (colony morphology) or R strain.
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