Scientists may soon be able to reduce the risk of deadly infection after a burst appendix, childbirth or bowel surgery.
Infection from bowel bacteria can set in after some operations
They have discovered how the particularly dangerous bacterium responsible for these infections is able to fool the body's defences.
The breakthrough could lead to new drugs to neutralise its effect.
The culprit, called Bacteroides fragilis, lives in huge numbers in normal healthy human intestines - it makes up as much as half of our faeces.
However, if the bugs escape into other parts of the body they cause serious infections.
We are in a race with the bacteria
Before effective antibiotics became available, up to a third of infections from thee bug proved fatal.
At present doctors can use one very effective antibiotic to fight these infections.
But some resistant bacteria have now appeared, and there is concern that resistance may spread as it has in other types of bacteria.
Microbiologist Dr Sheila Patrick, from Queen's University, Belfast, said: "We have discovered one of the genetic mechanisms that allows this bacterium to make an amazing
variety of components on its cell surfaces, which help it fool our defences.
"Only one other known bacterium, a type of Salmonella, uses a similar mechanism.
"We have also found out where all the genes are on the Bacteroides fragilis chromosome, and discovered what many of them
These two vital bits of information should allow the researchers to develop new effective antibiotics in the future, if the bacteria become more resistant to the ones in use at the moment.
Dr Patrick said: "It is vital that we can continue with operations such as hysterectomy and gastro-intestinal surgery, and can treat peritonitis after a burst appendix
or uterine infections after childbirth.
"We are in a race with the bacteria. If we do not come up with a winning strategy before resistance spreads, we could return to the pre-antibiotic levels of deaths from infection."
The research was a collaboration between Queen's University of Belfast, the University of Edinburgh and the Wellcome Trust Sanger Institute.
It was presented at the Society for General Microbiology's Spring Meeting in Edinburgh.