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•  Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells

•  Viruses lack a metabolism and cannot therefore be treated with antibiotics

Antibiotics are compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism

  • Metabolic features that may be targeted by antibiotics include key enzymes, 70S ribosomes and components of the cell wall
  • Because eukaryotic cells do not possess these features, antibiotics will target the pathogenic bacteria and not the infected host
  • Antibiotics may either kill the invading bacteria (bactericidal) or suppress its potential to reproduce (bacteriostatic)

Viruses do not possess a metabolism (they are not alive) and instead take over the cellular machinery of infected host cells

  • As such, they cannot be treated with antibiotics and must instead be treated with specific antiviral agents
  • Antiviral treatments target features specific to viruses (e.g. viral enzymes like reverse transcriptase or components of the capsid)

Antibiotic Targets in a Typical Prokaryote


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•  Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of  

    bacteria have multiple resistance

Since the discovery of the first antibiotic in 1928, antibiotic compounds have been used to treat a variety of bacterial infections

  • Antibiotics can be narrow spectrum (effective against specific bacteria) or broad spectrum (effective against many bacteria)

Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains have multiple resistance

  • Genes may confer resistance by encoding traits that degrade the antibiotic, block its entry, increase its removal or alter the target
  • Because bacteria reproduce at a rapid rate, resistant strains of bacteria can proliferate very quickly following the initial mutation
  • Additionally, resistant strains can pass resistance genes to susceptible strains via bacterial conjugation (horizontal gene transfer)

The prevalance of resistant bacterial strains is increasing rapidly with human populations due to a number of factors:

  • Antibiotics are often over-prescribed (particularly broad-spectrum drugs) or misused (e.g. given to treat a viral infection)
  • Many antibiotics are freely available without a prescription and certain antibiotics are commonly included in livestock feed
  • Multi-drug resistant bacteria are especially common in hospitals (i.e. nosocomial infections) where antibiotic use is high

An example of an antibiotic resistant strain of bacteria is Golden Staph (MRSA – Methicillin Resistant Staphylococcus aureus)

Development of Antibiotic Resistance

antibiotic resistance