Staphylococcus sp.
General: Commonly colonize the skin and mucosal membranes of mammals and birds. Composed of 35 species as of this writing, over half of which may be found in human clinical specimens.
Clinical: Coagulase- staphylococci are considered the leading cause of nosocomial infections, although also commonly overlooked as they are normal skin & mucosal flora and may produce a subtle, subacute illness. May form a biofilm on indwelling or implanted foreign bodies.
- Normal: Skin & mucosa, with some species particularly prone to certain niches.
- Abnormal: Wide spectrum; skin, soft tissue, bone, GU, blood.
Resistance: Usually S. aureus. Penicillins, including methicillin (MRSA); usually due to altered penicillin binding protein PBP2a, encoded by mecA gene, but may be due to overproduction of beta-lactamase. Vancomycin is usually used to treat MRSA, but intermediate resistant strains have developed (VISA - vancomycin intermediate S. aureus or GISA - glycopeptide intermediate S. aureus.)
Morphology: Catalase+, Gram+ cocci observed in pairs, clusters, and occasionally short chains, as are Micrococcus sp. which are in the same family, Micrococcaceae. (This is a morphologic similarity, as studies show them to not be genetically related.) Most are 0.5-1.5um, nonmotile, facultative anaerobes able to grow in high salt and at 18-40C. Most are coagulase-, except Staphylococcus aureus. Some have a polysaccharide capsule; there are multiple capsular serotypes.
Growth Characteristics: (See species for specific growth characteristics and variations.) Grow rapidly on blood agar at 35C over 24-48hrs with opaque white/cream colonies 1 - 8mm. S. aureus are usually cream but may produce classic yellow/golden colonies and may be beta-hemolytic. Mannitol salt agar helps discriminate S. aureus in mixed samples. Coagulase- staphylococci are generally non-hemolytic and usually cannot ferment mannitol.
Common/important pathogens:
- Staphylococcus aureus
- Staphylococcus epidermidis
- Staphylococcus haemolyticus
- Staphylococcus lugdunensis
- Staphylococcus saprophyticus
- Staphylococcus schleiferi
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