Staphylococcus

Genus Staphylococcus

Staphylococci comprises of 52 species, however not all of the members cause disease.Many of the members of the staphylococcus genera are considered to be normal flora on the skin and mucus membranes.Staphylococci are the most frequent bacteria associated with the production of pus.

The most medically important species:
Staphylococcus aureus.
Staphylococcus epidermidis.
Staphylococcus saprophyticus.

Microscopical characteristics

Gram stain: Staphylococci are Gram-positive, spherical cells (0.5-1.5 mm) cocci. Arranged in single, pairs, tetrad and irregular clusters. The grapelike orientation is the most common arrangement associated with the staphylococci. Staphylococci are non-motile, non-spore forming, non-capsulated bacteria.
Staphylococcus are aerobic and facultative an-aerobic, grow well on simple media.Colonies appear convex, circular opaque, smooth, moist with an entire edge and pigmented.
Staphylococcus are tolerant to salt (7-10% Nacl).Most stains produce golden pigmentation on Nutrient agar.

Mannitol salt agar (MSA)-
S. aureus ferments mannitol and appear as yellow colonies while Non- S. aureus (like S. epidermidis) does not ferments mannitol and so appear as pink colonies.

Staphylococcal capsule: The capsule protects the bacteria by inhibiting the chemotaxis and phagocytosis of staphylococci by polymorph nuclear leukocytes,It is also facilitates the adherence of bacteria to catheters and other synthetic material.

Staphylococcal enzymes:

Coagulase
Catalase
Hyaluronidase
Fibrinolysin
Lipases
Penicillinase