**3. Characteristics of the Staphylococcus**

Staphylococci are the most important micro-organisms in the Microccaceae family: they have been denominated by Ogston, as in microscopic slides their elements dispose themselves in clusters. They have a spherical form and are asporigenic and normally non-capsulated, gram-positive, aerobic and optionally anaerobic. It is easy to grow them on common culture media; optimal temperature is 37°C. They are among the most resistant germs to heating and disinfectants. With reference to the colony colours they are classed in aureus, albus, citreus and aurantiacus.

More recently they have been divided in aureus and epidermidis, as the former produces coagulasis and is able to ferment mannitol in anaerobic conditions. By phagic typisation 4 groups have been ascertained, whose major representatives in chronic bone pathologies are type 5 and type 8 [5].

Staphylococcus produces many extracellular substances that show almost all antigenic properties. The most interesting is coagulase that fosters a fibrin barrier around the staphylococcus that might oppose the action of phagocytes and opsonins [6].

It can also induce in the host a form of "allergy" that further reduces his defences [2–4]. It seems moreover that the bacterial resistance develops proportionally to its capacity to produce para-aminobenzoic acid, necessary to its metabolism, or producing its precursor folic acid. It is supposed that para-aminobenzensulfonamide displaces para-aminobenzoic acid from the bacterial body, i.e. owing to the antibiotic action the bacterial bodies may lose their strong cellular wall transforming themselves in sferoblasts with a weakened antigenic function or without any antigenic function, who are responsible for some infections with a chronic evolution.
