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 microbeplasmid 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 b
Contact: Don Powell
Wellcome Trust Sanger Institute