Staphylococcus aureus

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Staphylococcus aureus

Characteristics:
Gram:	Gram-positive cocci
Growth:	Facultative anaerobe
Spore:	No
Motility:	No
Catalase:	Positive
Oxidase:	N/A
Urease:	N/A
Nitrate:	N/A
Taxonomy:
Kingdom:	Bacteria
Phylum:	Firmicutes
Class:	Bacilli
Order:	Bacillales
Family:	Staphylococcaceae
Genus:	Staphylococcus
(See Pubmed Taxonomy database)
Synonyms:
Micrococcus pyogenes; Micrococcus aureus; Staphylococcus pyogenes

Introduction

ΕΤΥΜΟΛΟΓΙΑ

See also Staphylococcus. Latin "aureus" means 'golden-coloured' in reference to its naked eye colony appearance. The Staphyloxanthin carotenoid responsible for the colour impairs neutrophils, and is possibly an important part of the bacterium's pathogenicity.

One of the most important pathogenic gram positive organisms. Apart from being common, it also has the potential to produce toxins responsible for a range of different clinical presentations eg toxic shock, epidermolysis.

Antibiotic resistance is an important feature. MRSA stands for meticillin-resistant Staphylococcus aureus; MSSA stands for meticillin-sensitive (i.e. non-resistant) Staphylococcus aureus. (NB - meticillin was renamed recently - it used to be called methicillin.) In some communities in the US MRSA outnumbers MSSA.

Aetiology

Commonly found on the skin.

Microbiology

S. aureus is a Gram-positive coccus, which on microscopy, appears in clusters. It is a facultative anaerobe which grows readily on standard blood agar.

The Panton Valentine Leukocidin (PVL) gene is associated with invasive disease and is seen in a number of epidemic clones eg USA300.

Clinical

Commonly causes skin infections eg impetigo, cellulitis especially in broken or eczematous skin. Classically has a golden crust (see box). Bullous forms including Scalded skin syndrome due to epidermolytic toxins.

Rarely causes necrotizing pneumonia.

Responsible for many cases of osteomyelitis. Can also cause septic arthritis.

Bacteraemia with or without shock can occur. Toxic shock syndrome was originally described in relation to retained tampons but is now recognised with any focus of infection (not exclusively Staphylococcal).

Staphylococcal infective endocarditis has a high morbidity & mortality, and is on the increase globally due to increased use of intravascular catheters. With better imaging techniques, endocarditis complicating bacteraemia is being increasingly recognised.