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*Commensals on skin and mucous membranes of animals and man
*Commensals on skin and mucous membranes of animals and man
*Opportunistic pyogenic infections
*Enodgenous or exogenous infections
*Opportunistic pyogenic infections associa
*Coagulase-positive 'S. aureus'' and ''S. intermedius'' as well as ''S. hyicus'' are important pathogens of animals
*Coagulase-positive 'S. aureus'' and ''S. intermedius'' as well as ''S. hyicus'' are important pathogens of animals
*Comparatively stable in environment
*Fairly stable in environment
*Strains selective for particular species
===Characteristics===
*Clusters of Gram-positive cocci
*At least 30 species
*Facultative anaerobes
*Catalase positive, oxidase negative, non-motile
*Virulent strains are coagulase positive
*Grow on non-enriched media
*White or golden colonies
*''S. aureus'' and ''S. intermedius'' produce double haemolysis; they produce alpha-haemolysin and beta-haemolysin
*Alpha-haemolysin prouces a narrow zone of complete haemolysis, whereas beta-haemolysin produces a wide zone of incomplete haemolysis
*Haemolysins act as toxins
*''S. hyicus'' is non-haemolytic
*Coagulase-negative strains vary in ability to cause haemolysis
*Slide test to detect bound coagulase (clumping factor) on surface of bacteria; bacteria clump within 1-2 minutes
*Tube test detects free coagulase, secreted by bactera; positive result indicated by clot formation in tube following 24-hour incubation
*Biochemical tests to differentiate ''S. aureus'' and ''S. intermedius''
*PCR to differentiate species
===Pathogenesis and pathogenicity===
*Cause suppurative lesions
*Trauma or immunosuppression predispose to infection
*Capsular polysaccharide, teichoic acids and potein A prevent opsonisation and therefore phagocytosis
*Cell wall proteins bind fibronectin and fibrinogen, allowing bacteria to attched to damaged tissues
*Coagulase, DNase and protein A production mark pathogenicity
===Diagnosis===
*Clusters of bacteria in Gram-stained smears of pus
*Culture on selective blood agar and MacConkey agar
*No growth on MacConkey
*Colony characteristics, haemolysis, catalase and coagulase production
*Phage typing for epidemiological studies
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