Staphylococci

Staphylococci:
Ø Are gram-positive spherical cells usually arranged in grapes like cluster.
Ø Young cocci stain strongly gram-positive, on ageing turn to gram negative.
Ø Are non-sporing, non capsulated and non motile.
Ø Grow readily on variety of bacteriological media under aerobic and microaerophillic conditions.
Ø Though they grow rapidly at 370C but give pigmentation best at room temperature.
Ø Produces pigments, which vary form porcelain white(Staphylococcus epidermis) to deep golden yellow (Staphylococcus aureus). Intermediate shades also do occur
Ø Are metabolically very active as they ferment many carbohydrates producing lactic acid but not gas. Variation occur among the strains even their proteolytic activity also varies greatly.
Ø Relatively resistant to heat 500C for 30 minutes and 9% sodium chloride.
Ø Readily inhibited by certain dyes like gentian violet diluted 1:100,000.
Ø Sensitive to lysostaphin but resistant to lysozyme.
Ø Many strains are resistant to penicillin by the grace of enzyme b-lactamase which breaks b-lactam ring.
Ø Some may carry plasmid that confers the resistance to the broad spectrum antibiotics like tetracycline