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

• Some strains of bacteria produce enzymes which break down antibiotics.
• When it comes to IBDP Biology, they can still grow in its presence.
• Prolongs epidemics:
  • Lengthens the period of time that people are ill.
  • Increase risk of higher mortality rates.
• There are frequent instances of multiple resistances to antibiotics.
• These bacteria are extremely hazardous.
• EG MRSA - methicillin-resistant Staphylococcus aureus.

• In a large population of bacteria there are always a few bacteria with resistance to some antibiotics.
• New alleles arise by spontaneous mutations.
• Very rarely, a new enzyme is synthesised.
• It is likely that this is a variant of an enzyme previously involved in another metabolic pathway.
• Eg the production of penicillinase:
  • Cuts an amide bond in the penicillin molecule.
• In massive populations, the total number of mutations is large.
• Therefore, the chance of a benficial mutation is higher.
• Most bacteria will be killed by the antibiotic.
• Resistant strains are ‘selected for’.
• They can subsequently grow and multiply rapidly.
• Produces a population of bacteria:
  • All contain the resistance gene.
  • All resistant to the antibiotic.
• Resistance genes are often on plasmids.
• Bacteria can pass on the plasmids to other bacteria:
  • Conjugation tubes.
  • Between individuals of the same species.
  • And between different species.

• Cultures of the bacteria are grown on agar plates.
• Discs soaked on antibiotics can be placed on this.
• When it comes to IBDP Biology, the antibiotic diffuse into the agar.
• If they are bactericidal, a circular zone of resistance will develop around the disc.
• If the bacteria are resistant to an antibiotic, there will be a smaller or no resistance zone.

• Hospitals are more likely to develop resistant strains due to large numbers of patients being prescribed antibiotics.
• Over prescription of antibiotics:
  • Precautionary prescriptions to prevent secondary bacterial infections when a patient has a viral disease.
  • Pressure from patients for antibiotics when they are not really needed.
• Not completing a course of antibiotics prescribed.
  • Allows survival of some bacteria exposed to a sub-lethal concentration.
  • These rapidly multiply.
  • Large numbers of residual microorganisms are more difficult for phagocytes to destroy.
  • Higher chance of antibiotic resistant bacteria surviving.
• When it comes to IBDP Biology, it is common for people to hold onto unfinished prescriptions, and then for them to take these when they suspect they have a bacterial infection.
• Immuno-suppressed individuals:
  • Immune systems struggle to eliminate residual drug resistant bacteria.
  • Healthy individuals normally destroy these.
• In the past, antibiotics have been added to animal feed
  • They cause increased growth rates.
  • By modifying the balance of bacteria in the animals' gut.
  • Humans consumed the antibiotic.
  • This practice has been banned.

• Develop new antibiotics faster than resistant strains develop.
• Frog skins produce antibacterial chemicals.
• Develop other methods for destroying bacteria through genetic engineering.
• When it comes to IBDP Biology, in some cases, other ("second line") antibiotics are available:
  • These work in a different way.
  • They may bring infections under control.
• Keep some drugs as a last resort.
• Only use when everything else has failed.
• Bacteriophages are viruses that grow within bacteria.
• They kill the bacterial host in order to release the next generation of bacteriophages.
• Bacteriophages are incapable of infecting anything other than specific strains of the target bacteria.
• There is resurged interest in the use of these to destroy bacteria.

That's the end of this topic.

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