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The origins of life
Robert Miller Bacterial gene swapping in nature Sci Am Jan 1998
Bacteria reproduce very quickly. Under ideal conditions, Eschericia coli can complete a life cycle in 30 minutes.
Sex in bacteria
Bacteria do not show sexual reproduction as such but they do exchange genes forming new combinations. The principle way in which the bacteria exchange genes is by conjugation. This involves the transfer of genetic material (either from the main DNA loop or plasmids) via a cytoplasmic bridge between the two organisms.
This can be done between unrelated species of bacteria. Recent studies on bacteria in the wild show that it definitely occurs there - in the soil, in freshwater and oceans and inside living organisms.
The magic bullet
Antibiotics revolutionised medicine by improving the survival rates of patients suffering from infections.
The first antibiotic, penicillin, was discovered by Alexander Fleming in 1929. It was later isolated by Florey and Chain. It was not extensively used until the 2nd World War when it was used to treat war wounds.
After World War II many more antibiotics were developed. Today about 150 types are used. Most are inhibitors of the protein synthesis, blocking the 70S ribosome, which is characteristic of prokaryotes.
It took less than 20 years for bacteria to show signs of resistance. Staphylococcus aureus, which causes blood poisoning and pneumonia, started to show resistance in the 1950s.
Today there are different strains of S. aureus resistant to every form of antibiotic in use.
It seems that some resistance was already naturally present in bacterial populations but the presence of antibiotics in their environment in higher concentrations increased the pressure by natural selection.
Resistant bacteria that survived, rapidly multiplied. They passed their resistant genes on to other bacteria (both disease causing pathogens and non-pathogens)
Resistance genes are often associated with transposons, genes that easily move from one bacterium to another.
Many bacteria also possess integrons, pieces of DNA that accumulate new genes. Gradually a strain of a bacterium can build up a whole range of resistance genes. This is multiple resistance. These may then be passed on in a group to other strains or other species.
Antibiotics promote resistance
If a patient taking a course of antibiotic treatment does not complete it or forgets to take the doses regularly, resistant strains get a chance to build up.
The antibiotics also kill innocent bystanders bacteria which are non-pathogens. This creates more space for the resistant pathogens to expand.
The use of antibiotics also promotes antibiotic resistance in non-pathogens too. These non-pathogens may later pass their resistance genes on to pathogens.
Resistance gets around
When antibiotics are used on a person, the numbers of antibiotic resistant bacteria increase in other members of the family. In places where antibiotics are used extensively (e.g. hospitals and farms - 70% of antibiotic production is put in animal feed) antibiotic resistant strains increase in numbers.
Viral infections are not stopped by antibiotics. Yet doctors still prescribe (or are coerced into prescribing) antibiotics to treat them.
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