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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 |
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| + | ===Characteristics=== |
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| + | *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 |
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| + | ===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 |
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| + | ===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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| + | === |