MRSA is caused by the bacteria Staphylococcus Aureus
Staphylococcus Aureus
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MRSA is the term given to Methicillin resistant strains of the bacteria Staphylococcus Aureus, it is also used as a description for any strain of Staphylococcus bacteria which is resistant to one or more conventional antibiotic. It is an infection that is now endemic in almost every hospital in the UK. In 2004 100,000 of those who went into hospital contracted an infection there. Of those, 5,000 died and a very high proportion of these instances were related to MRSA infection.
MRSA infection is highly newsworthy in the UK and USA but the risks of succumbing to an MRSA infection should be put into perspective. MRSA rarely, if ever, presents a danger to the general public. It is no more dangerous or virulent than methicillin-sensitive S. aureus but it is more difficult to treat. It is usually, only when the bacterium comes into contact with vulnerable or debilitated patients that this infection will occur, therefore hospitalised patients are at higher than normal risk of picking up a Staphylococcal infection, firstly because the population in hospitals tends to be older, sicker and weaker than the general population, making them more vulnerable to the infection and secondly, conditions in hospitals, which involves a great many people sharing the same accommodation and being examined by doctors and nurses who have just touched other patients, are the perfect environment for the transmission of all manner of infections.
MRSA infections can cause a broad range of symptoms depending on the part of the body that is infected. These may include surgical wounds, burns, catheter sites, eye, skin and blood. Infection often results in redness, swelling and tenderness at the site of infection. Other diseases caused by staphylococci include boils, sinusitis, emesis, diarrhea, endocarditis, scalded skin syndrome, osteomyelitis, urinary tract infection, and toxic shock syndrome.
 MRSA infection as it worsens
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Staphylococcus aureus is a normal inhabitant of the skin and mucous membranes in the nose of a healthy human. Most patients from whom MRSA is isolated are colonised with this organism rather than infected. Colonisation means the presence of the organism on the skin, or in the nose, or in the back of the throat but without any illness. Individuals can become carriers of MRSA in the same way that they can become a carrier of ordinary Staphylococcus aureus which is by physical contact with the organism. If the organism is on the skin then it can be passed around by physical contact. If the organism is in the nose or is associated with the lungs rather than the skin it can be transmitted by droplets spread from the mouth and nose.
Shortly after penicillin became available in the late 1940s for treatment of serious staphylococcal infections, resistance to this antibiotic emerged and rapidly spread among strains of S. aureus and coagulase-negative staphylococci. The mechanism of resistance was the production of a plasmid-mediated beta-lactamase enzyme (a penicillinase) able to hydrolyze penicillin's beta-lactam bond. Currently, about 90% of S. aureus isolates are resistant to penicillin. Penicillinase-stable semi-synthetic penicillins (eg, methicillin and cephalosporins (eg, cephalothin sodium), were developed in the late 1950s and early 1960s to create beta-lactam antibiotics that are not inactivated by beta-lactamase. Methicillin was among the first of these agents to be introduced into clinical practice, but strains of MRSA were identified as early as 1961.
Methicillin is now no longer used except as a means of identifying this particular type of antibiotic resistance. During the 1970s a strain of Staphylococcus aureus resistant to methicillin, was isolated and consequently vancomycin (the most powerful antibiotic so far discoveredl) became the primary antibiotic used to combat staphylococcus infection. In 1997 a strain of S. aureus resistant to vancomycin was isolated. There are many different strains of MRSA, with differing degrees of immunity to the effects of various antibiotics. It doesn't mean that antibiotics are completely powerless against it - it may simply require a much higher dose over a much longer period, or the use of an alternative antibiotic to which the bacteria has less resistance.
MRSA has emerged because there are countless different strains of a single type of bacteria, and each has subtle natural genetic mutations which make it different from another and bacterial genes are constantly mutating. Some strains' genetic makeup will give them a slight advantage when it comes to fighting off antibiotic attack so when weaker strains encounter antibiotics, they die, while these naturally resistant strains may prove harder to kill Over time, the bulk of the Staphylococcus strains will carry resistance genes, and further mutations may only add to their survival ability. Strains that manage to carry two or three resistance genes will have extraordinary powers of resistance to antibiotics.
At present the future for MRSA hospital acquired infections is not looking good. The number of reports of MRSA infections rises year by year - and the latest evidence suggests that deaths due to MRSA are increasing at a similar rate and there is also the emergence of VRSA, or vancomycin resistant Staphylococcus aureus, which has acquired resistance to a drug considered the "last line of defence" when all other antibiotics have failed.
The UK has already seen several cases of GISA, or glycopeptide intermediate Staphylococcus aureus, an infection half way between MRSA and VRSA, which has developed a resistance to antibiotics of the vancomycin family.
Governments are already trying to at least slow down the effects of MRSA. Hospital cleanliness is the object of a major overhaul to improve overall standards of hygiene and simple handwashing between patients should be a must for doctors and nurses to prevent transmission. Family practitioners have now been told to cut antibiotic prescribing as one of the main reasons behind the bacterium’s swift evolution into "superbugs" is the overuse of antibiotics, both in human and veterinary medicine. Misprescription of antibiotics was strengthening the communities of bacteria in the patients’ systems.
Complete sequencing of the genomes of different S. aureus strains will provide better understanding of the features that make this bacterium resistant to antibiotics and the light it sheds on evolution in MRSA provides another tool to understand how diseases occurs and possibly to find new methods to combat them. See Karyn's Genomes for further information on S. aureus
LINKS TO FURTHER READING
http://www.link.med.ed.ac.uk/RIDU/Mrsa.htm
http://biology.kenyon.edu/Microbial_Biorealm/bacteria/gram-positive/staphylococcus/staphylococcus.htm
http://www.amm.co.uk/newamm/files/factsabout/fa_mrsa.htm
http://www.news-medical.net/?id=2811
http://www.postgradmed.com/issues/2001/10_01/simor.htm
SRS links to S. aureus genomes sequences in the EMBL database
http://srs.ebi.ac.uk/srsbin/cgi-bin/wgetz?-id+sessionId+[embl-des:staphylococcus&aureus&complete&genome]+-vn+3
SRS links to S. aureus genomes sequences in the Uniprot database
http://srs.ebi.ac.uk/srsbin/cgi-bin/wgetz?-id+sessionId+[uniprot-AllText:Staphylococcus&aureus&complete&genome]+-vn+3 |
