Staphylococci

Staphylococci are Gram positive cocci that occur in grape-like clusters. They are ubiquitous (present, appearing, or found everywhere) and form the most common cause of localised suppuration lesions in human beings. In hospital environment Staphylococci becomes most common human pathogen because of their ability to develop resistance to penicillin and other antibiotics.

Von Recklinghausen was the first one who observed Staphylococci in human progenitor lesions. It was Pasture, who culture cocci from pus and produced abscesses by inoculating them into rabbits. It was Sir Alexander Ogston, who gave it a name Staphylococcus (Staphyle, in Greek, meaning ‘bunch of grapes’: kokkos, meaning a berry) due to its typical occurrence in grape-like culture in pus and in cultures. Ogston noticed that non virulent staphylococci were also often present on skin surfaces.

Most staphylococcal strains from pyogenic lesions were found to produce golden yellow colonies, and the strains from normal skin, white colonies on solid media. Rosenbach (1884) named them Staph. Aureus and Staph. Albus respectively. Pasture (1885) described a third variety, Staph. citreus which produce lemon yellow colonies.

However, the association between virulence and pigment production was not found to be constant.

Many other properties of Staphylocooi were proposed as indicators of virulence. Which included hemolysis, gelatin liquefaction, lipolytic activity, production of urease, phosphatase and other, but non of these was found reliable. The most common association was between virulence and production of the enzyme coagulate, and to a lesser extent fermentation of mannitol.

Staphylococci were therefore classified into two groups: Staph. aureus (also called Staph pyogenes) containing strains giving a positive coagulase test, fermenting mannitol and usually being pathogenic, and Staph. epidermidis (also called as Staph. albus) containing coagulase negative, mannitol non fermenting and usually non pathogenic strains.

On the bases of chemical composition of cell wall components and other properties, genus Staphylococcus is now classified into 32 species and 15 subspecies. Beside Staph aureus, two coagulase negative species – Staph epidermidis, Staph haemolyticus and Staph saprophyticus can also cause human disease. Some other coagulase negative species such as staph hominid and Staph capitus are part of the commensal flora of the human skin. Other species are parasitic on animals.