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Methicillin resistant staphylococcus aureus (MRSA)

What is methicillin resistant staphylococcus aureus (MRSA)?

Staphylococcus aureus is a type of bacterium. Its most common site is the lower colon of humans. All children and 20-40 % of healthy human adults carry in it their noses and skin without causing any harmful effects. But in certain circumstances such as the rupture of skin this organism causes boils, wounds or serious infections such as pneumonia, and bacteraemia. Provided the immune systems are well it is unlikely that individuals will get a staphylococcal infection .

But within a hospital setting people are ill often with their immune system working at limited efficiency or they may have open wounds making access into the body easy therefore rendering the susceptibility to this organism greater. Sometimes the bacterium can get inside the body by synthetic devices such as urinary catheters or surgical implants.

Antibiotics were first discovered in 1928 and since then the 6000 or so antibiotics, which were either discovered or created, have successfully eliminated an enormous range of dangerous bugs. Most Staph..aureus strains can be easily eradicated using a common antibiotic.

The extensive use of antibiotics have caused certain resistant strains to evolve or the “once rare” resistant strains to flourish. Methicillin is a very potent antibiotic used successfully against most staphylococcal infections. MRSA is a staphlococcus aureus strain, which shows such resistance to many common antibiotics including Methicillin.

Therefore if a patient gets infected with this strain, eradicating can be a major problem as fewer antibiotics are available. It is important to note that MRSA like any other strain will not cause any problem while on people’s noses or skin unless they get inside through wounds etc.


A recent estimate in the US shows that around 80,000 people get an MRSA infection while in hospital. The number who will get colonised by it would be much greater since everyone who gets colonised does not necessarily get infected. It is those individuals whose immune systems are compromised that carry the greatest chance of suffering the most from an MRSA infection.

They fall into three categories:

  1. Very elderly people- whose immune system is weakened by age
  2. Very young people(infants and children)- whose immune system is not yet fully developed
  3. Sick people- whose immune system is weakened by existing disease such as HIV or those in intensive care units, orthopaedic or surgical wards.

Diagnosis – how to know if someone has it?

The only way is through laboratory examination of specimens, eg. skin swabs or urine sample. Normal staphylococci are identified as a yellow-gold gram-positive grape like bacterium, which occurs in pairs or clusters. MRSA detection is often difficult due to two different sub-populations, existing in the same culture. One being resistant and the other being not.

The standard screening test is to use an agar plate containing 6mg/ml of oxacillin and Mueller-Hinton agar supplemented with table salt, NaCl (4% w/v; 0.68 mol/L) and to check if the organism grows or not. If the organism grows then it is resistant to Oxacillin. Oxacillin is very similar to methicillin and those strains that are resistant to oxacillin are often resistant to Methicillin as well. Another test is the use of a polymerase chain reaction to detect a gene contained within MRSA bacterium called, mec-A. This gene is associated with the bacteria’s resistance to methicillin.

How MRSA spreads

MRSA can always spread and cause infection in those whose immune systems are weak. The method of spread is always by physical contact from hands and rarely through air. The main preventive step taken in hospitals is to isolate the MRSA infected patient from other patients.


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Written by Dr. Ozair (CEO of SignSymptom.com) as physician writers are physicians who write creatively in fields outside their practice of medicine.

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