Staphylococcus

Staphylococcus: د. زينب عادل چـابك
م. جوان احمد علي الهماوندي
They are Gram-positive, non-motile, non-spore forming, and occasionally capsulated. They are spherical cocci which are arranged in grape-like irregular clusters due to cell divisions occur in three planes, it may also found in single, pair or short chains specially when grow in liquid media, they produce pigments that vary from white to deep yellow. Catalase positive, oxidase negative, it is aerobic and facultative anaerobic.
Some staphylococci are part of the normal flora, they are present on skin and in the mucous membranes, but others can cause suppuration, abscess formation, pneumonia and meningitis. The most common type of food poisoning is caused by staphylococcal enterotoxin. Staphylococci rapidly develop resistance to many antimicrobial agents and cause difficult therapeutic problems.
There are three important species of staphylococcus: Staphylococcus aureus, Staphylococcus epidermidis (albus), and Staphylococcus saprophyticus (citrus).

Morphology and Culture characters:
Staphylococcus aureus cells approximately 1µm in diameter and divided to form cluster, some stains are capsulated. On blood agar, it forms colonies 1-3mm in diameter, round, smooth, raised, and glistening and surrounded by beta hemolytic zone. On mannitol salt agar it form colonies about 1mm in diameter, the colony are yellow surrounded by yellow region due to acid formation, also Staphylococcus aureus grows with NaCl in concentration 7.5-10% that inhibit most types of other bacteria.