E.coli bacteria can cause serious infection
The number of urinary tract infections and cases of blood poisoning caused by drug resistant E.coli bacteria has jumped sharply.
The Health Protection Agency has recorded more than 400 cases in the past 12 months.
Prior to 2003, just a few cases were recorded at its labs each year.
The HPA has launched an investigation into the rise, and will report its findings later this year.
The infections are caused by strains of E. coli that produce enzymes called extended-spectrum-beta-lactamases (ESBL).
These enzymes enable the bugs to destroy, and thus become resistant to, certain antibiotics.
ESBL-producing E. coli still only account for a very small proportion of all urinary tract infections.
However, it is important that they are recognised rapidly, so patients can be given drugs that do work.
The HPA stresses that, as it not mandatory to report cases of ESBL E. coli infection, the true extent of the problem is still unclear.
It is aware that some patients who have been infected have died - but cannot say whether the infection was a direct cause of their death.
Professor Pat Troop, HPA chief executive, said: "It is important that health professionals and laboratories are aware of this problem so that the correct testing can be carried out and that patients are given the most effective treatment.
"There are very few antibiotics that remain effective in the treatment of these infections, and for some patients it is necessary for them to receive hospital treatment so that intravenous antibiotics can be given.
"Therefore, we in the Agency are taking ESBLs very seriously and have issued advice already to laboratories to help them in the detection of these infections.
"We have also alerted GPs to the need to send specimens to a laboratory if a patient's infection is not responding to first-line antibiotic treatment.
"Our specialists have also been working closely with colleagues in other countries to determine how significant a new threat these infections represent."
Professor Troop said for most people a UTI, although unpleasant, is easily treatable and they will make a full recovery.