In the US each year, at least 2 million people become infected with drug-resistant bacteria and around 23,000 people die as a result. But now, researchers have looked into horizontal gene transfer - also known as bacterial sex - to unveil why it can lead to the spread of traits including antibiotic resistance.
The researchers, led by Prof. Kevin Foster of Oxford University in the UK, publish their findings in the journal Nature Communications.
He and his team explain that while it has been known that horizontal gene transfer is key in microbial evolution, why it has such a strong effect has puzzled scientists.
"It is well known that bacteria are able to swap little pieces of DNA," says Prof. Foster, "which is crucial for them to be able to evolve and adapt to new environments, including responding to antibiotics."
He adds that it is "different to sex in humans, but the effect - swapping genetic material - is similar."
According to the team, however, bacterial sex is very rare - only one cell among millions actually swaps DNA. In theory, any strain that is resistant will rapidly divide and "take over the community," stopping opportunities to share the resistance gene.
"But it does keep happening," says Prof. Foster, "and genes are often able to hop through diverse groups of different bacteria. Until now, the mystery has been why."
Migration is the 'missing ingredient'
To further investigate why, he and his colleagues - including René Niehus, a DPhil student in the Department of Zoology at Oxford University - created a mathematical model to investigate the conditions that are necessary for bacterial sex to continue taking place.
- Antibiotics have been used for the last 70 years, but infectious organisms have adapted, making the drugs less effective
- Each year in the US, 2 million people are infected with antibiotic-resistant bacteria
- And at least 23,000 people die as a result of these infections.
Niehus explains that they wanted to answer the question: "How does a function like antibiotic resistance keep hopping between bacteria?"
Previous research into this topic ignored the fact that these communities are open, says Niehus.
However, their model shows that migration is the missing ingredient, and that "this very high immigration rate among bacteria gives a huge opportunity for different microbes to meet and swap DNA, even though it's a rare event when taken in isolation."
The team notes that such migration between bacteria communities can happen anywhere, including the human body or soil.
Additionally, this migration can involve the ability to survive in an environmental toxin, in addition to developing antibiotic resistance.
Their model has helped the researchers observe that "the highest rates of horizontal transfer will occur for ecologically important traits that are under positive natural selection."
Niehus succinctly explains:
"The key point is that a bacterial system with continual immigration of strains will allow traits like antibiotic resistance to spread much more easily between different species of bacteria. Our model offers a theoretical framework for understanding the processes behind this spread."
Medical News Today recently reported on a new antibiotic resistance gene found in China that likely originated in animals and subsequently spread to humans.
Researchers from that study said Chinese leaders need to "act rapidly and decisively" in order to avoid a "public health problem of major dimensions."