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USA300 strain of S. aureus

The USA300 strain of Staphylococcus aureus bacteria, colorized in gold, shown outside a white blood cell.

Staphylococcus aureus: USA:300 is a strain of gram-positive coccus bacteria responsible for Methicillin-resistant Staphylococcus aureus (MRSA), or Staph infection in humans. This strain of S. aureus is resistant to β-lactam antibiotics. When cultured, this bacteria appears as golden clusters. The golden color is the result of a carotenoid pigment that protects the bacteria against host-immune system reactive oxygen species, and adds to the bacteria's virulence. S. aureus is a facultative anerobe, which can be found in a wide variety of locations such as soil, human skin, and public places like hospitals and prisons. This strain of S. aureus: USA 300 was first identified in 1998, and is thought to be the primary causal strain of community-acquired Staph infections throughout the United States, Canada and Europe. In 2006 the CDC reported that 64% of MRSA isolated from infected patients were of the USA 300 strain. This bacteria contains the cytotoxin Panton-Valentine leukocidin (PVL), which targets leukocytes. It also contains modulin, which is a phenol-soluble peptide (PSM) that is capable of lysing neutrophilic granulocytes. These toxins cause rapidly-progressing fatal conditions such as necrotizing pneumonia and faciitis and severe sepsis. USA:300 causes an estimated 20-40 thousands deaths annually and worldwide.

Photo Credit: RML/NIAID
Content Credit: http://microbewiki.kenyon.edu

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