Pharmaceutical firms have been urged to develop new drugs to fight infections after experts warned of the increasing resistance of germs to antibiotics.
The Health Protection Agency (HPA) is concerned that the number of effective treatments available may run out. It is particularly worried about a group of bacteria called "gram-negative", which includes E. coli, which has a growing resistance to antibiotics.
E. coli is the commonest cause of urinary tract infections, causing about 70-80% of all cystitis cases. It is also the cause of many bloodstream infections.
There are about 20,000 E. coli bloodstream infections each year in England, Wales and Northern Ireland, of which about 12% (2,400) are resistant to antibiotics.
In 2000, about 4% of E. coli bloodstream infections were resistant but this has risen to 12% in 2006.
The HPA experts said this was because new types of resistant genes have developed in the E. coli bacteria.
Dr David Livermore, laboratory director at the HPA Centre for Infections, said E. coli was the "big beast".
He said steps could be taken to help tackle the problems including making sure antibiotics are prescribed appropriately and not given for common coughs and colds.
Doctors should also make sure that hospital patients get the right drugs at the right dose for the right length of time.