In this topic of IBDP Biology, we will learn about antibiotics.

Definition: substances produced by some micro-organisms which are in some way lethal to other micro-organisms.

• Produced by moulds:
  • Slow growing cells.
  • Antibiotics provide competitive advantage against other micro-organisms;
  • Usually bacteria - which grow fast.
• Purified forms of antibiotics are more or less harmless to most humans.
• Act on some aspect of the growth of micro-organisms.
• The metabolic pathways are different to human cells.
• Do not affect ordinary mammalian cells.

• First antibiotic to be developed.
• Several versions of Penicillin.
• Variations on a common formula.
• Produced by different strains of Penicillium spp.
• Or, by using different culture media.
• Or they can be synthesised.
• Differ in the efficacy and ease of use in different applications.
• When it comes to IBDP Biology, all inhibit the production of cell walls by bacteria:
  • Bind to an enzyme, transpeptidase.
  • Prevent synthesis of cross links between petidoglycan polymers.
  • The bacteria die due to osmotic lysis.
  • They are bactericidal, i.e. it kills the bacteria.

• Various other antibiotics have also been developed.
• Eg streptomycin:
  • Produced by Streptomyces species.
  • Discovered soon after Penicillin.
• When it comes to IBDP Biology, some are bacteriostatic, i.e. inhibit the growth of bacteria.
• Different modes of action:
  • Interfering with bacterial protein synthesis:
    • Streptomycin binds to ribosomes.
    • Causes mRNA codons to be misread.
  • Some interfere with nucleic acid synthesis.

• When it comes to IBDP Biology, different diseases are treated with different antibiotics.
• Strains of some bacteria are resistant to several antibiotics.
• Essential that antibiotics are not over administered.
• Antibiotic screening is used to select the most effective antibiotics for particular bacteria.
• Broad spectrum antibiotics:
  • Effective against a wide range of bacteria.
  • Eg tetracyclines and chloramphenicol.
• Narrow spectrum antibiotics:
  • Effective against a few bacteria.
  • Eg penicillin (effective against Gram-positive bacteria)

That's the end of this topic.

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