By Nick Triggle
Health reporter, BBC News
The NHS is being warned about its use of antibiotics
The rise in antibiotic resistance is reaching worrying levels, experts say.
The Health Protection Agency said while the focus on infections such as MRSA had been largely successful, new trends in other bugs were now posing a threat.
For instance, 12% of bloodstream infections by E. coli in England, Wales and Northern Ireland now show some signs of not responding to drugs.
The HPA said the NHS must be careful over antibiotic use and urged industry to look into developing new drugs.
There are two main families of bacteria known as Gram-positive, such as MRSA, and Gram-negative, which includes E. coli and other less common bugs Acinetobacter and Pseudomonas.
The HPA said there had been a drive to tackle MRSA in recent years which had helped reduce infection rates and led to a host of new antibiotics to be developed.
By comparison, the development of antibiotics targeting Gram-negative bacteria such as E. coli, which can cause a range of symptoms from mild diarrhoea to abdominal cramps and kidney damage, was much less common.
The fight against drug resistance is an on-going battle because many bacteria constantly mutate, gaining resistance to current antibiotics in the process.
This is what has been happening in recent years to the likes of E. coli.
HPA data show that there are about 20,000 bloodstream infections of E. coli each year - although the true level of infections would be much higher if urinary tract infections were taken into account.
Of these, 12% show signs of resistance - up from about 4% at the turn of the century.
The infections are mostly not yet resistant to all forms of antibiotics, just what doctors call the first-line.
This means they are having to use back up drugs, which tend to have more side effects and raises the prospect of the widespread emergence of a new strain which is totally antibiotic resistant.
Indeed, reports have already emerged of such a scenario in Israel and the US, while four cases have been reported in the UK.
Dr David Livermore, an infections expert at the HPA, urged industry to start looking at developing new antibiotics.
But he added: "The NHS must be careful over its use of antibiotics to slow down the development of resistance.
"Hospitals must make sure they use the right dose, for the right length of time.
"GPs should not prescribe - nor patients expect - antibiotics for routine coughs and colds.
"Resistance has been accumulating. We are having to use reserve antibiotics more than previsously... that is worrying.
"There are some cracks in the system, but they are not big ones yet."
A spokesman for the Association of the British Pharmaceutical Industry said drug firms were working hard to develop new antibiotics.
He pointed out they were supporting the work of the Infectious Disease Research Network, a group of NHS academics which is exploring ways of developing new treatments.
"The pharmaceutical industry has always been the driving force behind the discovery of new medicines."