Scientists have identified "super strains" of a potentially fatal lung infection which affects cystic fibrosis patients.

Up to 80% of adults with CF are infected with the bacterium Pseudomonas aeruginosa , and must constantly take antibiotics in a bid to keep the infection - which often proves fatal - at bay.

Most acquire their own unique strain of the organism but in recent years doctors have noticed the development of strains that can be passed from one CF patient to another.

Patients can develop these "super strains" even if they already have their own strain of Pseudomonas.

The emergence of bacteria that are resistant to many antibiotics is an extremely worrying trend

Dr David Bull, Cystic Fibrosis Trust

Some of the transmissible strains are also resistant to some antibiotics, making them harder to control.

Scientists say the development could have significant implications for antibiotic usage in treating and preventing Pseudomonas, and for infection control procedures for CF patients.

New challenge

The latest research into the subject will be presented to the annual conference of the Public Health Laboratory Service in Warwick on Tuesday.

There are around 7,500 cystic fibrosis patients alive in the UK.

The organism Pseudomonas aeruginosa is present in the natural environment, and causes no problems for healthy people.

But in people with CF it is a major cause of lung disease, leading to potentially fatal inflammation of the lungs.

Some strains are being transmitted between small clusters of patients attending particular cystic fibrosis clinics

Dr Tyrone Pitt, PHLS

Most will develop the infection, but doctors aim to delay them contracting it for as long as possible by giving them prophylactic antibiotics.

Dr Tyrone Pitt, deputy director of the PHLS Laboratory of Hospital Infection at the Central Public Health Laboratory in London, told BBC News Online: "Pseudomonas aeruginosa is probably the most significant contributor to the demise of most CF patients."

Now, he says, transmissible strains are also providing a new challenge.

"The suggestion is that there are clusters of strains and some strains are being transmitted between small clusters of patients attending particular CF clinics."

Segregation

A survey of 650 patients found three variations of the bacteria. These have been named after the centres where they were first identified.

Up to 30 cases of the "Birmingham" strain have been identified in the city.

But around 50 cases of the "Liverpool" strain and 10 cases of the "Manchester" strain have been seen elsewhere.

Clinics already segregate infected patients from non-infected to try to limit the spread of the infection.

But Dr Pitt said worries over the transferable strains could have further implications for CF patients and their carers.

"The problem is that segregation is expensive, for example, seeing patients on different days and at different clinics."

He said fears about transmission of these "super strains" could also impact on patients' everyday lives.

"They are very supportive of each other and there's a lot of mixing because it helps them cope with the disease."

DNA tests

Dr Pitt said there were many questions about these new strains.

"Are these transmissible strains any more dangerous to the patients than the others, the normal strains that they pick up in their everyday life?

"And can these transmissible strains 'super-infect on top of the natural ones that they would get anyway?"

This is suspected in a small number of cases, but much more work needs to be done using DNA technology to look at what makes these strains different, he said.

Reliance on antibiotics

Dr David Bull of the Cystic Fibrosis Trust told BBC News Online: "The emergence of bacteria that are resistant to many antibiotics is an extremely worrying trend.

"Young people with CF suffer from recurrent chest infections because their lungs don't work properly and they are incredibly reliant on antibiotics.

"As the bacteria become resistant, the antibiotics become less effective. So stronger drugs, and combinations of drugs have to be used to treat their chest infections.

"It becomes much more difficult to treat these bacteria and the infections spread very quickly between CF sufferers."

He added: "Cross-infection is a huge problem. The average life-expectancy for a young person with CF is just 31 years of age. But these superbugs mean that mean survival rate could be under threat."