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Scientists commented on the research, published in Science, into the toxin-producing strain of MRSA bacteria known as PVL, which is normally community acquired and can lead to severe pneumonia.
Dr Ronald Cutler, Principal Lecturer in Infectious Diseases and Pathology, University of East London, said:
“The importance of Panton-Valentine Leukocidin (PVL) in Staphylococcal pneumonia is complex and sometimes controversial. Recently the association of PVL positive CA-MRSA with rapid deaths in young adults has been a major cause of worry.
“Briefly, the paper by Labandeira-Rey and others reports that in animals PVL, a toxin known to kill white blood cells, can additionally stimulate to the production of other dangerous Staphylococcal toxins that inflame the lung (Protein A).
“The appearance of PVL toxin in severe Staphylococcal pneumonia is a recent phenomenon. Previously the toxin was only found in less than 5% of strains.
“In 2005 it was reported that PVL positive strains were associated with multiple skin lesions in healthy young adults however its role in pneumonia was unsure and workers in the US demonstrated that in animals, skin infections were equally severe using either PVL positive or negative strains.
“The paper in Science Express demonstrated that PVL positive strains have the potential to cause pneumonia but there may be still other factors involved for example, a recent study in man concluded that CA-MRSA pneumonia in previously healthy adults was usually associated with influenza.
“I feel the situation remains complex, however a clearer understanding of how PVL positive CA-MRSA can cause disease may help us to develop more effective treatments, especially since recent reports suggest that poor penetration of major antibiotics into the lung have led to treatment failures of up to 40%, and this combined with the recent spread of PVL positive CA-MRSA in a UK hospital are naturally further grounds for concern.”
Dr Jodi Lindsay, Senior Lecturer at Centre of Infection, St George’s, University of London, said:
“PVL toxin is produced by most strains of community acquired-MRSA (CA-MRSA), but not by typical MRSA in hospitals. CA-MRSA are a major problem in the USA, cause severe skin and soft tissue infections (such as boils and abscesses) in healthy people, and there are documented outbreaks in sporting teams, prisons, the military, homosexuals, gym users, and IV drug users. Rarely, CA-MRSA causes fatal pneumonia (lung infection) in children, most of these cases have been reported in Europe. In the UK, a few cases of CA-MRSA have been reported, and the incidence seems to be rising.
“The importance of PVL to these diseases is currently debated amongst scientists. This study suggests PVL might be important for pneumonia. Another study has recently suggested PVL is not so important for skin infections. It is likely there will be a lot more research done in the next few years to sort out the role of this toxin, and the role of many other toxins produced by MRSA.
“Just to clarify, contrary to the press release from the journal Science, CA-MRSA have not escaped from hospitals. The CA-MRSA have evolved independently in the community and did not originate in hospitals.”
Dr Marina Morgan, Consultant Medical Microbiologist, Exeter, said:
“Doctors can no longer confidently predict who is likely to have MRSA. infection. For really sick, septic patients, we cannot rely on the traditional targeted, “sniper” approach of narrow spectrum antibiotics. but have to use the ‘big guns’ up front, at least until we are certain it’s not MRSA.
“PVL production turbo-charges the destructive capability of MRSA. This paper proves what those of us who manage PVL-staph infected patients already knew. PVL is strong enough on its own to destroy the lungs.
“Killing the MRSA bug whilst closing down its internal PVL toxin-assembly line is easy. PVL- associated skin infections are usually relatively easily dealt with, and even if the bug gets into the bloodstream, we can inactivate PVL toxin with infusions of antibodies (immunoglobulin). The real problem with PVL-MRSA is that PVL toxin itself is immune to antibiotics. The reason most patients die is that despite killing the bug, PVL toxins already formed continue to digest lung tissue, so we desperately need some way of removing the toxins.”
Dr Mark Enright, Reader in Molecular Epidemiology, Imperial College, said:
“Panton Valentine leukocidin (PVL) strains of MRSA are emerging as a major threat to healthy people of all ages around the world. PVL strains can cause a particularly lethal disease called necrotizing pneumonia and unlike other MRSA, PVL strains are not associated with hospitals. These strains are extremely aggressive and to make matters worse they also spread rapidly from person to person.
“In this study Labandeira-Rey and co-workers demonstrate why this may be. On work in mouse models they show that PVL alone is enough to cause severe pneumonia but in the bacterium it also interacts with other cellular systems to promote the production of other factors that cause severe inflammation and tissue damage. Not only that but PVL causes the bacteria to produce proteins that make it ‘stickier’ – enabling it to attach firmly to human tissue promoting its spread within the human population.”
Professor Richard James, Director of the Centre for Healthcare Associated Infections, University of Nottingham, said:
“This paper again illustrates that superbugs are formidable enemies who have amazingly sophisticated weapons, or even combinations of weapons, to attack us with. In combination with their ability to rapidly acquire resistance to our major weapon, antibiotics, you can see why we might be feeling more like David than Goliath is this battle.
“The results of this work highlight the urgent requirement for tests that can distinguish HA-MRSA from CA-MRSA that can be used in NHS Diagnostic Microbiology laboratories. At the moment we have no screening for CA-MRSA in the community, and no rapid detection of PVL and other toxins in hospital strains of S.aureus in the UK.
“The dramatic increase in PVL producing community-associated MRSA (CA-MRSA) in healthy young children in Texas has so far been associated with skin and soft tissue infections. Prior viral infection may increase susceptibility to necrotizing pneumonia, thus an influenza epidemic could trigger much more serious infections.
“With PVL producing strains of S.aureus it is important to treat the patient with antibiotics that block expression of the PVL toxin as quickly as possible in order to reduce the lung damage.
“Given the scale of the problem of healthcare associated infections in the UK it is a real surprise how little research funding has been allocated to increase our basic understanding of superbugs and to help develop new treatments.”