We can now get the same information immediately, at home or in the doctor's office, and we're working on similar ways to detect dozens of other potentially harmful bacteria

Professor Ben Miller, Rochester University

Professor Ben Miller, from the University, said the sensor represented the first major improvement in testing for Gram-positive and -negative bacteria since a laboratory technique first used in 1884.

He said: "It's amazing to me that we're still using a procedure that's effectively out of the Stone Age.

"We can now get the same information immediately, at home or in the doctor's office, and we're working on similar ways to detect dozens of other potentially harmful bacteria."

The "smart dressing" picks out a molecule called lipid A which is found on the surface of the cells of Gram-negative bacteria.

The researchers have created another molecule which binds with lipid A to make a subtle colour change.

It is hoped that once the test is fine-tuned, it could be read by a computer, so could be used by the patient at home to monitor cuts and wounds for signs that dangerous bacteria were invading.

'Step forward'

Alice Pentland, who runs the department of dermatology at Rochester, said: "This is an important step in changing the way preventive medicine is perceived and practiced.

"This research can put a very simple and accurate tool into the hands of anyone, giving them more control over their own health than ever before."

A spokesman for the Public Health Laboratory Service said that the present invention would not necessarily be able to pick out the good guys from the bad guys among the bacteria.

He said: "In order to inform treatment, one would need to be able to tell whether the bacteria are pathogens - that is, capable of causing disease - or simply harmless bacteria.

"If pathogens are present, it would also be important to know whether they are actually in a place where they might cause disease as opposed to simply being present but not posing a risk of infection."

The team from Rochester says there has also been interest in the technology from food packaging manufacturers - so that it could give a colour-change warning if meat had gone rotten.

Plastic cups could include the sensor so that water could be checked for purity.