Stealth technology maintains fitness after sex

Jan 12, 2007

Pathogens can become superbugs without their even knowing it, research published today in Science shows. 'Stealth' plasmids - circular 'DNA parasites' of bacteria that can carry antibiotic-resistance genes - produce a protein that increases the chances of survival and spread of the antibiotic-resistant strain.

Low-cost plasmids, described for the first time in the study are a threat to use of antibiotics.

Plasmids are naturally occurring 'DNA parasites' of many bacterial species and have been known about for over 30 years. Some are able to transfer themselves from one bacterial cell to another through a sex-like process called conjugation, contributing to bacterial evolution. Worryingly, as well as copying themselves plasmids can pick up and transfer bacterial genes, such as those that make pathogens resistant to antibiotics.

However, the plasmid comes at a cost to the host bacterium: gaining a plasmid can reduce the host's ability to grow and reduce its fitness. When antibiotic treatment is stopped, the new microbe–plasmid combination will be eliminated quickly through fierce competition from more 'fit', plasmid-free bacteria.

The research teams, led by Professor Charles J. Dorman at Trinity College Dublin, Ireland, and Dr John Wain at the Wellcome Trust Sanger Institute in Cambridge, UK, have discovered that an important class of plasmids use a stealth gene (called sfh) to allow entry into a new bacterium with minimal reduction in fitness.

With the low-cost version of the resistance plasmid they have described in Salmonella, resistant bacteria are likely to survive and the resistance genes to persist even if antibiotic therapy is stopped.

Their research shows that sfh codes for a protein that is very similar to another bacterial protein: the role of the protein is to organise the genetic material in bacterium and control activity of many genes, including those involved in causing disease. The sfh protein binds to the new plasmid DNA, preventing its detection by the bacterium.

"The bacterial protein, called H-NS, is a very important molecule and affects the way a bacterial pathogen operates. By bringing in its own supply of the H-NS-like stealth protein (called Sfh), the plasmid avoids interfering with the natural balance of H-NS and DNA in the cell," explained Professor Dorman.

"Our work suggests that bacterial fitness can be manipulated by altering the proportions of H-NS and DNA in the cell, perhaps through the use of drugs, an insight that may be exploited in the future to prevent or to fight infection."

Bringing its own supply of the host-like protein is clearly an advantage for the plasmid, suggesting that the normal supply of H-NS in the bacterium may become limited when new DNA is imported. If a modified plasmid, lacking the sfh gene, is transferred to Salmonella, the effects of the plasmid are very rapidly detected.

Bacteria can acquire and transfer resistance genes through a variety of methods, but this new study shows how a single gene has the potential to increase dramatically the chance of successful - and health-threatening - transfer and survival of a battery of antibiotic-resistance genes.

The consequences for managing disease - especially in developing countries - are significant, explained Dr John Wain: "These plasmids are found in many pathogenic bacteria including those that cause typhoid and paratyphoid fever. Both of these diseases are increasing in the developing world and in the UK we are seeing more and more imported cases.

"But understanding is not enough: we now need to exploit this information to try to prevent the plasmid spreading any further."

Source: Wellcome Trust Sanger Institute

Explore further: Big city life: New leafhopper species found on a threatened grass in New Jersey

Related Stories

Bacterial genome scalpel can identify key gene regions

Jun 15, 2015

In a study that twists nature's arm to gain clues into the varied functions of the bacterial genome, North Carolina State University researchers utilize a precision scalpel to excise target genomic regions that are expendable. ...

How bacterial cell recognizes its own DNA

Apr 13, 2015

It may come as a bit of a surprise to learn that bacteria have an immune system - in their case to fight off invasive viruses called phages. And like any immune system - from single-celled to human - the ...

New mechanisms of 'social networking' in bacteria

Apr 07, 2015

Bacteria have traditionally been viewed as solitary organisms that "hang out on their own," says molecular biologist Kevin Griffith of the University of Massachusetts Amherst. However, scientists now realize ...

Recommended for you

Study shows grey squirrels are quick learners

7 minutes ago

They may be viewed by some as an invasive species or a commonplace pest of public parks, but a new study from the University of Exeter has shown that grey squirrels are actually quick learners capable of ...

Waiting to harvest after a rain enhances food safety

42 minutes ago

To protect consumers from foodborne illness, produce farmers should wait 24 hours after a rain or irrigating their fields to harvest crops, according to new research published in the journal Applied and Environmental Microbiology.

Can gene editing provide a solution to global hunger?

3 hours ago

According to the World Food Program, some 795 million people – one in nine people on earth – don't have enough food to lead a healthy active life. That will only get worse with the next global food cris ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.