Micrococcus luteus

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Gram stain Culture

Sir Alexander Fleming
"one sometimes finds what one is not looking for"

General information
- Micrococcus was discovered by Sir Alexander Fleming before he discovered penicillin 1928
  
  Taxonomy
  Family: Micrococcaceae
  
  Natural habitats
  Micrococci are widespread in nature and are commonly found on the skin of humans and other mammals.
  
  They are generally believed to be temporary residents and are most frequently found on the exposed skin of the face, arms, hands, and legs.
  
  Clinical significance
  They thought of as harmless or commensal organism, though it can be an opportunistic pathogen, there have been rare cases of infections in people with compromised immune systems, as occurs with HIV patients.
Gram stain
- Gram positive cocci,
  
  0.5-1.8 µm,
  
  occurring mostly tetrads, and irregular clusters.
  
  Mature cells lose the ability to retain the crystal violet, which makes them decolorization easier than younger cells.
Culture characteristics
- Obligate aerobic
  
  BA: after 48 hours the colonies are 1-2 mm in diameter (grow more slowly than staphylococci).
  
  Colonies dull or matte, convex and bright yellow, and a small percentage are crème-white.
  
  McConkey: growth
  
  BBAØ: no growth
Characteristics
References
- James Versalovic et al.(2011) Manual of Clinical Microbiology 10th Edition