Antibiotics

3 Key excerpts on "Antibiotics"

• 

  eBook - ePub

  Biotechnology

  An Illustrated Primer

  • Rolf D. Schmid, Claudia Schmidt-Dannert, Ruth Hammelehle(Authors)
  • 2016(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Occurrence. ~10,000 Antibiotics have been isolated from microorganisms, another 10,000 from basidiomycetes and lower fungi, and 10,000 more from higher organisms, especially plants but also lichen and animal and marine invertebrates. Actinomycetes by far outnumber all other organisms in their capacity to synthesize Antibiotics.

  Applications. Only ~300 Antibiotics are produced industrially. They are mostly semisynthetic compounds, in which a biologically active lead structure is modified chemically. β-Lactam Antibiotics (penicillins and cephalosporins) (→206) make up about half of a world market of >42 billion US$ and some 50,000 t (2009). Most Antibiotics are manufactured as antimicrobial agents for chemotherapy. They can be classified as broad-spectrum Antibiotics, affecting a wide range of pathogens (e. g., cephalosporins, tetracyclines), and selective Antibiotics, used for highly special therapies (e. g., rifampicin against tuberculosis, amphotericin B against fungal infections). Antitumor Antibiotics, such as adriamycin, are valuable cytostatic agents, but also exhibit high toxicity. Several Antibiotics are used for plant protection. They are often effective in lower concentrations than herbicides and show low toxicity against mammals. Examples are blasticidin S and kasugamycin. Only a few Antibiotics are used in food preservation, such as pimaricin, which is sometimes used as an antifungal agent in cheeses. Feed Antibiotics lead to a better mast performance and faster growth in mass animal production, but are usually restricted for feed use (e. g., monensin in broiler production), to prevent clinical cross resistance. In molecular biology, Antibiotics serve as a research tool for the selective inhibition of various cell functions.

  Antibiotics: screening, industrial production, and mechanism of action

  Screening.

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  eBook - ePub

  Bacterial Pathogenesis

  A Molecular Approach

  • Brenda A. Wilson, Malcolm Winkler, Brian T. Ho(Authors)
  • 2019(Publication Date)
  • ASM Press

    (Publisher)

  natural products, to distinguish them from compounds that arise solely by chemical synthesis. Naturally occurring Antibiotics are almost all products of secondary metabolism and are often produced in response to environmental stress or competition with other microbes. With the recent dearth of new Antibiotics, there has been a resurgence of screening for new natural-product Antibiotics from microbial and untapped eukaryotic sources, such as marine organisms. However, screening for antibiotic activity from natural products is challenging because the source material can vary from batch to batch and natural-product extracts are usually complex mixtures of chemicals that need to be fractionated to find active compounds. In addition, it should always be kept in mind that Antibiotics synthesized by bacteria bring the complication that the producer species must have its own intrinsic mechanism of resistance. Therefore, operons imparting resistance to natural-product Antibiotics are already out there in nature and can become a serious problem if they are genetically transferred from the producer bacteria to pathogens treated with the Antibiotics.

  The fact that bacteria produce Antibiotics has raised the question of what the role of antibiotic production in nature is. An obvious explanation is that Antibiotics are a kind of “germ warfare,” in which the producing species use antimicrobial compounds to discourage microbial competitors. The problem with this widely accepted explanation is that antibiotic production by microbes growing in nature is so low that levels of Antibiotics are undetectable under many conditions. An alternative explanation for the role of antibiotic production in nature is that bacteria use these compounds as signaling molecules. Although there is no definitive experimental basis yet for either the germ warfare theory or the signaling theory, there is growing evidence that bacteria use antibiotic-like compounds as signals. Recent studies indicate that Antibiotics can modulate gene transcription and specific adaptive responses in bacteria in a dose-dependent manner, suggesting that these Antibiotics may have a role in cell-to-cell communication.

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  eBook - ePub

  Treatment of Endodontic Infections

  • José F. Jr Siqueira, Isabela N. Rôças(Authors)
  • 2022(Publication Date)
  • Quintessenz Verlag

    (Publisher)

  Table 19-1 ). If these principles are not adhered to, the treatment will not work and undesirable side effects may occur.

  Mechanisms of antibacterial action

  Some Antibiotics kill bacteria (bactericidal) while others inhibit bacterial growth (bacteriostatic). Each type of antibiotic performs its effect through a specific mechanism of action (Table 19-2 ). Bactericidal Antibiotics kill bacteria, inhibiting cell wall synthesis (β-lactams, vancomycin, bacitracin, etc), disrupting the cytoplasmic membrane (polymyxins, polyenes, etc), or acting on DNA (metronidazole, quinolones). Bacteriostatic Antibiotics, on the other hand, inhibit bacterial growth, inhibiting protein synthesis (aminoglycosides, chloramphenicol, macrolides, tetracyclines, lincosamides, etc) or exerting antimetabolite activity, e.g. by inhibiting folic acid synthesis (sulfonamides, trimethoprim, etc). While the distinction between bactericidal and bacteriostatic agents appears to be clear according to the in vitro definition, this only applies under strict laboratory conditions and is inconsistent for a particular agent against all bacteria.42 Bacteriostatic Antibiotics can exhibit bactericidal effects at high concentrations. Although bacteriostatic/bactericidal data may provide valuable information on the potential action of antibacterial agents in vitro, it is necessary to combine this information with pharmacokinetic and pharmacodynamic data to provide a more meaningful prediction of efficacy in vivo. The ultimate guide to treatment of any infection must be clinical outcome.45

  β-lactam Antibiotics (penicillins and cephalosporins), which are the most widely used Antibiotics in the treatment of endodontic infections, kill bacteria by inhibiting cell wall synthesis. The action of β-lactams especially occurs during the active growth of the bacteria, at which time the bacterial cell wall is synthesized. β-lactams inhibit transpeptidases, which are the enzymes that catalyze the crosslinking of peptidoglycan molecules. Peptidoglycan crosslinking is essential for the bacterial cell wall to be rigid, and to protect the bacterium from osmotic lysis. β-lactams competitively inhibit transpeptidases by binding to these enzymes as alternative substrates. Transpeptidases act as penicillin-binding proteins (PBPs). In addition, the β-lactams–PBP complex stimulates the release of autolysins, which are enzymes that digest the existing cell wall. This results in the destruction of the cell wall and the death of the bacteria by osmotic lysis (cytolysis).

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