MRSA

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MRSA

• Methicillin Resistant Staphylococcus aureus.
• This bacteria, to which 20-30 of the population
  are carriers for, typically lives on the skin or
  inside the nose.
• It can cause a range of diseases, from minor skin
  infections to life-threatening pneumonia.
• Can grow in the presence of many antibiotics,
  including penicillins, and cephalosporins.

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Staphylococcus aureus

• Gram positive coccus that grows in grape like
  clusters.
• Growth usually has a golden-yellow color to it,
  hence its latin name which means golden seed.
• Facultative anaerobe that produces catalase.
• Act as oppurtunistic pathogens.

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The Infection

• S. aureus causes infections when normal skin
  barriers or mucosal linings have been breached.
• The problem with staph infections is the toxins
  the bacteria release.
• These toxins can interfere with the immune
  system, break down proteins, and interfere with
  cell membranes and cause cell death.

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Skin Infections

• The first sign of a staph infection is usually a
  boil or a pimple.
• Staph can produce exfoliative toxins, which have
  protease (protein breaking down) activity that
  cause skin peeling.
• This is especially damaging in young children who
  can suffer from scalded skin syndrome. This can
  even occur as an epidemic in hospital nurseries.

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Scalded Skin Syndrome
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Beneath the Skin

• If the bacteria get access to beneath the skin,
  ie blood, lungs toxins are produced that break
  down cells.
• Many of the deadly MRSA infections seen over the
  last year have been positive for the bi-component
  toxin Panton-Valentine leukocidin(PVL).
• The PVL factor is encoded into S. aureus
  chromosome by a bacteriophage, (a virus that
  targets bacteria)

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PVL

• PVLs genes produce two proteins that combine
  with each other in our cell membranes to create
  porins, which cause the cells contents to leak
  out leading to cell death.
• This is responsible for the necrotizing (flesh
  eating) characteristics of staph associated skin
  lesions.

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Other Factors

• S. aureus can also produce a toxin known as
  Protein A which can prevent phagocytosis, kill B
  lymphocytes, and cause inflammation.
• Some toxins also act as superantigens, which
  cause huge immune responses, with no specific
  target.
• These immune responses are effectively worthless
  and only aid the bacteria in evading the immune
  system.