Plasmids Play a Larger Role in Antibiotic Resistance than Previously Believed

A team of scientists has just found that plasmids contribute more to antibiotic resistance than previously believed. Plasmids, which allow bacteria to exchange DNA segments, speed up antibiotic resistance and spread novel genes between bacterial colonies. The details are in a paper that was just published in the journal Nature Ecology & Evolution.

Antibiotics are used to prevent and treat many types of bacterial infections. The discovery of antibiotics was a major scientific breakthrough that helped fight dangerous diseases such as tuberculosis. The misuse and overuse of antibiotics is a major contributor to antibiotic resistance, however. Constant exposure to common antibiotics allows bacteria to build up resistances and these “superbugs” are a serious danger to human health.

Researchers from the University of Oxford studied the evolution of antibiotic resistance in Escherichia coli bacteria. The team exposed the bacterial colonies to an antibiotic called ceftazidime. The researchers specifically used bacteria with a gene that can mutate to provide ceftazidime resistance. Some of the bacterial colonies carried the gene in their chromosomes while others had plasmids containing the gene. Plasmids are small circular segments of DNA that can replicate and transfer genes between bacteria. The team compared the evolution of antibiotic resistance between the two groups of E.coli.

The researchers found that the group of bacteria with mutation-containing plasmids gained a resistance to ceftazidime much faster than the other colonies. The presence of the plasmids sped up evolution by providing the bacteria with extra gene copies. As the plasmids replicated, more copies of the mutated gene could be picked up by bacteria in the colony.

The findings show that plasmids are critical in helping bacteria gain antibiotic resistance. The authors don’t have a solution to this problem but hope their discovery will lead to follow-up studies. By better understanding plasmids and bacterial evolution, it may be possible to develop new types of treatments.


Millan et al. Multicopy plasmids potentiate the evolution of antibiotic resistance in bacteria. Nature Ecology & Evolution (2016).

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