A deadly mutant bug could be spreading among the public warn experts. The deadly strain of Methicillin-Resistant Staphylococcus Aureus (MRSA) called USA300 passes easily through skin-to-skin contact. It can also survive on surfaces and so has the potential to be picked up on crowded buses and tubes. The first cases were seen in the US but cases are now being reported in the community and not just hospitals in Britain.
According to Dr Ruth Massey, from the Department of Biology and Biochemistry at the University of Bath, extra vigilance was required around this and similar MRSA bugs known as PVL-positive community acquired strains. USA300 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. MRSA stands for Methicillin-resistant Staphylococcus aureus and is one member of the Staphylococcus family of common bacteria found on everyone’s skin.
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. He said, “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… They don't rely on healthcare workers moving them around, which the hospital ones seem to.” He added that USA300 is a really big issue in the U.S. 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),” he said.
In a new research paper published in the Journal of Infectious Diseases, Dr Massey and colleagues analyze the way community-acquired MRSAs are able to adapt and fine tune themselves to spread outside of hospitals.
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. Using a sensing system, it carefully controls when it switches on its ability to do this, so as not to cause disease until it is firmly established within the human. Many antibiotics target the cell walls of harmful bacteria, and to resist this, the bacteria have to make changes to their cell wall.”
Justine Rudkin, a PhD student working on the project, said, “The community-acquired bacteria has evolved further, and is able to maintain a higher level of toxicity while also resisting treatment from antibiotics, making it a much larger problem…While we are constantly learning more about MRSA, there is a serious threat posed by this newer strain of bacteria capable of causing disease and even death in perfectly healthy people. We need to respond seriously to this threat as it reaches Britain from the United States.” Rudkin says the new strain, which caused 18,650 deaths in the US in 2005 and can be brought here by carriers, is resistant to antibiotics.
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.” He said there was now a “need to worry about community super bugs that are fine tuned to spreading outside of hospitals and we all need to be extra vigilant about hygiene and unnecessary use of antibiotics.”
A spokeswoman for the Health Protection Agency (HPA) said, “The paper highlights some important observations which helps us understand at the molecular level why hospital strains of MRSA are less virulent than the so-called community MRSA strains. 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 research group is seeking funding to find treatments for community-acquired MRSA. The American Medical Association’s journal, JAMA, estimated there were 18,650 MRSA deaths in the US in 2005. Office for National Statistics data showed there were 485 deaths in England and Wales in 2010 where the superbug was mentioned on the death certificate. The figure represents a 38% fall from 2009 and is almost four times less than the 1,652 peak recorded in 2006.
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