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Thou art a boil, A plague sore, an embossed carbuncle In my corrupted blood.

—Shakespeare: King Lear

Members of the genus Staphylococcus (staphylococci) are Gram-positive cocci that tend to be arranged in grape-like clusters (Figure 24–1). Worldwide, Staphylococcus aureus is one of the most common causes of acute purulent infections. Other species are common in the skin flora, but produce lower grade disease, typically in association with some mechanical abridgment of the host such as an indwelling catheter.

FIGURE 24–1.

Staphylococcus aureus. Gram stain showing the Gram-positive cocci in clusters resembling bunches of grapes (arrows) and neutrophils (arrowhead). (Image contributed by Professor Shirley Lowe, University of California, San Francisco School of Medicine, with permission.)


Although staphylococci have a marked tendency to form clusters (from the Greek staphyle, bunch of grapes), some single cells, pairs, and short chains are also seen. Staphylococci have a typical Gram-positive cell wall structure. Like all medically important cocci, they are nonflagellate, nonmotile, and non–spore-forming. Staphylococci grow best aerobically but are facultatively anaerobic. In contrast to streptococci, staphylococci produce catalase. More than one dozen species of staphylococci colonize humans; of these, S aureus is by far the most virulent. The ability of S aureus to form coagulase separates it from other, less virulent species (Table 24–1). It is common to lump the other species together as coagulase-negative staphylococci (CoNS).

TABLE 24–1Features of Human Staphylococci

Staphylococci form clusters and are catalase-positive

Coagulase distinguishes S aureus from other species

Staphylococcus Aureus



In growing cultures, the cells of S aureus are uniformly Gram-positive and regular in size, fitting together in clusters with the precision of pool balls. In older cultures, in resolving lesions, and in the presence of some antibiotics, the cells often become more variable in size, and many lose their Gram positivity.

The cell wall of S aureus consists of a typical Gram-positive peptidoglycan interspersed with considerable amounts of teichoic acid. The peptidoglycan of the cell wall is commonly overlaid with polysaccharide and surface proteins. Although thin polysaccharide capsules are frequently present, their significance in ...

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