MRSA Support Group

Methicillin-resistant Staphylococcus aureus (MRSA), asometimes referred to as a super staph infection, is a specific strain of the Staphylococcus aureus bacterium that has developed antibiotic resistance to all penicillins, including methicillin and other narrow-spectrum β-lactamase-resistant penicillin antibiotics. MRSA was first discovered in the UK in 1961 and is now widespread, particularly in the hospital setting where it is commonly termed a superbug.

MRSA may also be known as oxacillin-resistant Staphylococcus aureus (ORSA) and multiple-resistant Staphylococcus aureus, while non-methicillin resistant strains of S. aureus are sometimes called methicillin-susceptible Staphylococcus aureus (MSSA) if an explicit distinction must be made.

S. aureus most commonly colonises the anterior nares (the nostrils) although the respiratory tract, open wounds, intravenous catheters and urinary tract are also potential sites for infection.

MRSA infections are usually asymptomatic in healthy individuals and may last from a few weeks to many years. Patients with compromised immune systems are at significantly greater risk of a symptomatic secondary infection.

Vancomycin and teicoplanin are glycopeptide antibiotics used to treat MRSA infections. Teicoplain is a structural congener of vancomycin that has a similar activity spectrum but a longer half-life (t½). Both drugs have low oral absorption thus are administered intravenously for systemic infections, with the exception of pseudomembranous colitis where vancomycin can be given by mouth for this GI tract infection.

Several new strains of MRSA have been found showing antibiotic resistance even to vancomycin and teicoplanin; those new evolutions of the MRSA bacteria are dubbed vancomycin intermediate-resistant Staphylococcus aureus (VISA). Linezolid, quinupristin/dalfopristin, daptomycin, tigecycline are more recent additions to the therapeutic arsenal, generally reserved for severe infections which do not respond to glycopeptides. Less severe infections may be treated by oral agents including: linezolid, rifampicin+fusidic acid, pristinamycin, co-trimoxazole (trimethoprim+sulfamethoxazole), doxycycline, and clindamycin.

Up to 53 million people are thought to carry MRSA. Scientists estimate that around 2 billion people, some 25-30 percent of the world's population, have a form of the Staphylococcus aureus bacteria.

Because cystic fibrosis patients are often treated with multiple antibiotics in hospital settings, they are often colonised with MRSA, potentially increasing the rate of life-threatening MRSA pneumonia in this group. The risk of cross-colonisation has led to increased use of isolation protocols among these patients. In a hospital setting, patients who have received fluoroquinolones are more likely to become colonised with MRSA,[10] this is probably because many circulating strains of MRSA are fluoroquinolone-resistant, which means that MRSA is able to colonise patients whose normal skin flora have been cleared of non-resistant Staph. aureus by fluoroquinolones.

In the US there are increasing reports of outbreaks of MRSA colonisation and infection through skin contact in locker rooms and gymnasiums, even among healthy populations. MRSA also is becoming a problem in paediatrics, [7] including hospital nurseries.

MRSA causes as many as 20% of Staphylococcus aureus infections in populations that use intravenous drugs. These out-of-hospital strains of MRSA, now designated as community-acquired, methicillin-resistant staph. aureus, or CA-MRSA, are not only difficult to treat but are especially virulent. CA-MRSA apparently did not evolve de novo in the community, but represents a hybrid between MRSA which escaped from the hospital environment and the once easily treatable community organisms. Most of the hybrid strains also acquired a virulence factor which makes their infections invade more aggressively, resulting in deep tissue infections following minor scrapes and cuts, and many cases of fatal pneumonia as well.

As of early 2005, the number of deaths in the United Kingdom attributed to MRSA has been estimated by various sources to lie in the area of 3000 per year. The staphylococcus bacteria accounts for almost half of all UK hospital infections. The issue of MRSA infections in hospitals has recently been a major political issue in the UK, playing a significant role in the debates over health policy in the general election held in that country in 2005.

During the summer of 2005, researchers in The Netherlands discovered that three pig farmers or their families were infected by MRSA bacteria that were also found on their pigs.[7] Researchers from Radboud University Nijmegen are now investigating how widespread the MRSA bacteria is in pigs, and whether it will become characterised among the zoonoses.

Recently, it has been observed that MRSA can replicate inside of Acanthamoeba, increasing MRSA numbers 1000-fold. Since Acanthamoeba can form cysts easily picked up by air currents, these organisms can spread MRSA via airborne routes. Whether control of Acanthamoeba in the clinical environment will also help to control MRSA, remains an area for research.