Antibiotic Resistance (Cambridge International AS Biology)

Resistance to Antibiotics: An Outline

Spec point — 10.2.2 · discuss the consequences of antibiotic resistance and the steps that can be taken to reduce its impact

Resistance to antibiotics

• Genetic variation exists between individuals in a bacterial population

  • This is the result of random mutation

• A chance mutation might give rise to a new allele that provides resistance to an antibiotic

  • E.g. some pathogenic bacteria have become resistant to penicillin
  • They have acquired ****an allele that codes for the production of an enzyme which breaks down penicillin

• When the bacterial population is treated with this antibiotic** any bacteria with the resistance allele do not die**

  • The antibiotic acts as a selection pressure

• The resistant bacteria can continue to reproduce with less competition from the non-resistant bacteria, which are now dead

• The allele for antibiotic resistance is passed on with much greater frequency to the next generation

  • This can occur especially quickly in bacterial populations, due to:

    • short generation times
    • all offspring being clones of their parents
    • horizontal gene transfer

• The antibiotic resistance allele increases in frequency

  • A higher proportion of the bacterial population is now resistant to the antibiotic

• This is an example of evolution by natural selection

Bacteria evolve rapidly due to their high mutation rate and short generation times; this means that antibiotic resistance can arise quickly when a population is exposed to a new antibiotic

• Humans have caused an increase in the occurrence of antibiotic resistance

  • This is because treating infections with antibiotics provides a selection pressure which drives natural selection

• This problem is made worse when antibiotics are used improperly, e.g.

  • For treatment of non-serious infections
  • For treatment of viral infections
  • Routine treatment to animals in agriculture
  • A course of antibiotics is not fully completed

Exam Hint Be careful when describing the development of antibiotic resistance; there are two major pitfalls to look out for:

• Antibiotic resistance mutations occur by chance, and not as the result of exposure to antibiotics; you should never say that antibiotics* cause *mutation
• Mutation gives rise to a new resistance allele, and not a new gene