Superbug strains increase outside hospitals

Dr Ruth Massey, from the Department of Biology and Biochemistry at the University of Bath, said extra vigilance was required around PVL-positive community acquired MRSA strains, including USA300, which has spread across the United States and is now seen in the UK.

USA300 is a form of the superbug which can lead to a flesh-eating type of pneumonia, and passes easily through skin-to-skin contact.

It is resistant to treatment by several front-line antibiotics and can cause large boils on the skin.

In severe cases, USA300 can lead to fatal blood poisoning or a form of pneumonia that can eat away at lung tissue.

Dr Massey said there were 1,000 cases of PVL-positive community acquired MRSA in England in the last year, of which 200 were USA300 strains.

“These community-acquired strains seem to be good at affecting healthy people – they seem to be much better than the hospital ones at causing disease,” Dr Massey said.

“They don’t rely on healthcare workers moving them around, which the hospital ones seem to.”

Dr Massey said USA300 was “causing huge problems in America and is being reported here increasingly”.

She added: “It’s a really big issue in the US and it’s starting to emerge here.

“But hopefully because we are aware of it and are working to understand it, it won’t become as big of a problem (in the UK).”

In a new research paper published in the Journal of Infectious Diseases, Dr Massey and colleagues analyse the way community-acquired MRSAs are able to adapt and fine tune themselves to spread outside of hospitals.

MRSA bacteria in hospitals has not been able to migrate into the community in the same way.

Dr Massey said: “Our research found that the composition of the cell wall of the bacteria is critical to the community-acquired bacteria being more toxic.

“The ability of the MRSA bacteria to secrete toxins is one of the main ways it causes disease.”

Community-acquired MRSA strains have cell walls that are different to those seen in hospitals, allowing them to sense their environment and switch toxin expression on at the right time.

Chris Thomas, professor of molecular genetics at the University of Birmingham, said: “The key message is that strains of MRSA that are spreading in the community are better able to infect the young and healthy, precisely because they are not actually trying so hard to be resistant as the bugs that have been encountered in hospitals for many years.”

A spokeswoman for the Health Protection Agency (HPA) said: “We have known about community MRSA for over a decade and, whilst they are responsible for a high burden of disease in North America, this is not the case in the rest of the world. In England we have seen sporadic cases of this type of MRSA most often causing boils and abscesses, but it has not emerged as a major public health issue in this country.

“The HPA are carrying out active surveillance of this type of bacteria and advise healthcare professionals on correct infection control procedures to reduce the likelihood of spread.”

The HPA said it had seen 150 to 200 cases of USA300 per year over the past three years.