Dangerous liaisons: bacterial ‘sex’ causes antibiotic resistance

Pneumococci with DNA from other species are more resistant to antibiotics, says study - News Release

Imperial College London News Release

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Thursday 11 June 2009

Some disease-causing bacteria are becoming resistant to antibiotics because they have peculiar sex lives, say researchers publishing new results today in the journal Science. The new study helps scientists understand how bacteria develop resistance to antibiotics, which is a major challenge for those treating infectious diseases, say the authors from Imperial College London.

Today’s research looks at bacteria called pneumococcus (Streptococcus pneumoniae), which cause diseases including pneumonia and bacterial meningitis. Pneumococcal infections cause approximately one million deaths every year globally and the bacteria are becoming resistant to many antibiotics, making treatment increasingly difficult. The scientists behind today’s study believe this resistance is due to the pneumococcal bacteria adapting by occasionally picking up DNA from other bacteria, even from other species.

Dr William Hanage, the lead author of the study from Imperial College London, said: “Bacteria have very peculiar sex lives. When humans have kids they mix up their DNA with that of their partner, but bacteria can pick up DNA from all sorts of places, even other species. Our research shows that bacteria which do this, that is undergo sex, with their own and other species are more likely to develop resistance to antibiotics, protecting them from being killed by these drugs."

Bacteria reproduce asexually, by splitting in two to produce identical ‘daughter’ cells. Sometimes, however, they can take up DNA from other bacteria or the environment, and incorporate it into their own genome. This mixing process, called recombination, is what happens in animals during sexual reproduction. It is most common between bacteria of the same species but, unlike animals, bacteria can sometimes undergo recombination with different species of bacteria, which means the daughter cells end up with DNA from those species.

Some combinations of DNA help bacteria to survive better. It appears that antibiotic resistant strains of pneumococcus are more likely to mix up their DNA in this way, and so are more likely to hit upon the adaptation which helps them resist antibiotic treatment.

Bacteria with mixed DNA are more likely to be resistant to antibiotics, say scientists

Dr William Hanage added: “Antibiotic resistance is a growing problem, particularly for potentially dangerous pneumococcal infections. Our new findings help us to understand how bacteria can wriggle their way out of tight spaces, finding ways to evade the drugs we bombard them with. Ultimately, we hope that we could use this knowledge to limit the emergence of new types of antibiotic resistance.”

The researchers examined DNA from 1,930 different S. pneumoniae strains, as well as three closely related species, S. mitis, S. pseudopneumoniae and S. oralis collected by a method called Multi Locus Sequence Typing (MLST). They were able to find strains with DNA which suggested recombination, or the mixing of DNA with other members of the same species, and other closely related ones.

The researchers then compared these results with data on resistance to the commonly-used antibiotics penicillin, erythromycin, tetracycline, chloramphenicol and cefotaxime. They found that bacteria with mixed DNA were more likely to be resistant to antibiotics, suggesting a link between recombination and antibiotic resistance.

This research was funded by The Royal Society, a BBSRC studentship and a grant from the Academy of Finland.

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Notes to editors:

1. “Hyperrecombination, Diversity, and Antibiotic Resistance in Pneumococcus”, Science, 12 June 2009

2. The Royal Society is an independent academy promoting the natural and applied sciences. Founded in 1660, the Society has three roles, as the UK academy of science, as a learned Society, and as a funding agency. It responds to individual demand with selection by merit, not by field. As we prepare for our 350th anniversary in 2010, we are working to achieve five strategic priorities, to:
* Invest in future scientific leaders and in innovation
* Influence policymaking with the best scientific advice
* Invigorate science and mathematics education
* Increase access to the best science internationally
* Inspire an interest in the joy, wonder and excitement of scientific discovery

3. About BBSRC

The Biotechnology and Biological Sciences Research Council (BBSRC) is the UK funding agency for research in the life sciences. Sponsored by Government, BBSRC annually invests around £450M in a wide range of research that makes a significant contribution to the quality of life for UK citizens and supports a number of important industrial stakeholders including the agriculture, food, chemical, healthcare and pharmaceutical sectors. BBSRC carries out its mission by funding internationally competitive research, providing training in the biosciences, fostering opportunities for knowledge transfer and innovation and promoting interaction with the public and other stakeholders on issues of scientific interest in universities, centres and institutes.

The Babraham Institute, Institute for Animal Health, Institute of Food Research, John Innes Centre and Rothamsted Research are Institutes of BBSRC. The Institutes conduct long-term, mission-oriented research using specialist facilities. They have strong interactions with industry, Government departments and other end-users of their research.

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