• When humans experience a pathogenic bacterial infection they are often prescribed?antibiotics?by a healthcare professional
• Antibiotics are chemical substances that?inhibit or kill bacterial cells?with little or no harm to human tissue
  • Antibiotics are derived from naturally occurring substances that are harmful to prokaryotic cells (structurally or physiologically) but usually do not affect eukaryotic cells
  • The aim of antibiotic use is to aid the body’s immune system in fighting a bacterial infection
• Penicillin?is a well-known example; it was the first antibiotic to be discovered in 1928 by Sir Alexander Fleming
• Antibiotics are either described as being?bactericidal?(they kill) or?bacteriostatic?(they inhibit growth processes), they target prokaryotic features but can affect both pathogenic and mutualistic bacteria living on or in the body
• However, like in all species, there exists?genetic?diversity?within populations, and the same applies to disease-causing bacteria
• Individual bacterial cells may possess?alleles?that confer?resistance to the effects?of the antibiotic
  • These alleles are generated through random?mutation?and are not caused by antibiotic use, but antibiotic use exerts selection pressures that can result in the increase in their frequency
• Bacteria have a single loop of DNA with only?one copy of each gene?so when a new allele arises it is immediately displayed in the phenotype
• When?an antibiotic is present:
  • Individuals with the allele for antibiotic resistance have a massive?selective advantage?so they are more likely to survive, reproduce and pass their genome (including resistance alleles) on
  • Those without alleles are less likely to survive and reproduce
  • Over several generations, the?entire population?of bacteria may be antibiotic-resistant
• Antibiotic resistance is an important example of natural selection

Staphylococcus

• There are known populations of the bacterium?Staphylococcus?that possess alleles which make them resistant to the effects of penicillin
  • These are known as?resistant strains
• Due to the?rapid reproduction rate?of bacteria (generations of 20-30 minutes for some species in optimal conditions) a single resistant bacterium can produce 10 000 million resistant descendants within a day

The future of antibiotic resistance

• Antibiotic-resistant strains are a major problem in human medicine
• New resistant strains are constantly emerging due to the?overuse of antibiotics
  • By using antibiotics frequently, humans exert a?selective pressure?on the bacteria, which supports the evolution of antibiotic resistance
• Scientists are trying hard to find?new antibiotics?that bacteria have not yet been exposed to, but this process is expensive and time-consuming
• Some strains of bacteria can be?resistant to multiple antibiotics?and they create infections and diseases which are very difficult to treat
• When antibiotics were discovered, scientists thought they would be able to?eradicate?bacterial infections, but less than a century later a future is being imagined where many bacterial infections cannot be treated with current medicines