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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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#REDIRECT[[:Category:Staphylococcus species]]
<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
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===Overview===
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*Commensals on skin and mucous membranes of animals and man
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*Enodgenous or exogenous infections
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*Opportunistic pyogenic infections associated with trauma, immusuppression, other infections
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*Coagulase-positive ''S. aureus'' and ''S. intermedius'' as well as ''S. hyicus'' are important pathogens of animals
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*Fairly stable in environment
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*Strains selective for particular species
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*Cause mastitis, tick pyaemia, exudative epidermitis, botryomycosis and pyoderma
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===Characteristics===
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*Clusters of Gram-positive cocci
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*At least 30 species
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*Facultative anaerobes
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*Catalase positive, oxidase negative, non-motile
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*Virulent strains are coagulase positive
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*Grow on non-enriched media
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*White or golden colonies
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*''S. aureus'' and ''S. intermedius'' produce double haemolysis; they produce alpha-haemolysin and beta-haemolysin
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*''S. hyicus'' is non-haemolytic
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*Coagulase-negative strains vary in ability to cause haemolysis
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*Slide test to detect bound coagulase (clumping factor) on surface of bacteria; bacteria clump within 1-2 minutes
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*Tube test detects free coagulase, secreted by bactera; positive result indicated by clot formation in tube following 24-hour incubation; free coagulase converts prothrombin to thrombin which converts fibrinogen to fibrin
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*Biochemical tests to differentiate ''S. aureus'' and ''S. intermedius''
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*PCR to differentiate species
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===Pathogenesis and pathogenicity===
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*Cause suppurative lesions
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*Trauma or immunosuppression predispose to infection
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*Capsular polysaccharide, teichoic acids and potein A prevent opsonisation and therefore phagocytosis
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*Cell wall proteins bind fibronectin and fibrinogen, allowing bacteria to attched to damaged tissues
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*Coagulase, DNase and protein A production mark pathogenicity
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*Haemolysins made by ''S. aureus'' and ''S. intermedius'' act as toxins
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*Alpha-haemolysin prouces a narrow zone of complete haemolysis; this toxin causes necrosis and targets mast cells and plasma cells, whose contents cause damage
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*Beta-haemolysin produces a wide zone of incomplete haemolysis; damages membranes and causes leakage, contributing to necrosis
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*Also gamma and delta toxins
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*Toxic shock syndrome toxin acts as a superantigen, which causes T cell proliferation and production of cytokines, leading to cardiovascular shock, with microthrombus formation in capillaries
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*Enterotoxins produced by some strains of ''S. aureus'' cause food poisoning in humans
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*Proteases, hyaluronidases and lipases facilitate survival of bacteria and spread and tissue destruction
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===Diagnosis===
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*Clusters of bacteria in Gram-stained smears of pus
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*Culture on selective blood agar and MacConkey agar
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*No growth on MacConkey
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*Colony characteristics, haemolysis, catalase and coagulase production
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*Phage typing for epidemiological studies
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===Bovine mastitis===
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*''S. aureus'' is a common cause of mastitisin cattle worldwide
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*Most infections subclinical
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*Systemic infection can occur with peracute and gangrenous forms
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*In gangrenous mastitis, the quarter may become necrotic and slough off; alpha toxin causes necrosis of smooth muscle in blood vessel walls, reducing blood flow to the affected quarter, and causes release of lysomal enzymes from leukocytes
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===Tick pyaemia===
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*Infection of lambs with ''S. aureus'' in hill-grazing areas of the UK
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*Lambs carry ''S. aureus'' on their skin and nasal mucosa; infection via skin trauma including tick bites
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*''Ixodes ricinus'' tick acts as a vector for ''Ehrlichia phagocytophila'', which causes immunosuppression in lambs, predisposing to staphylococcal infection
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*Acute septicaemia and death or localised abscess formation in many organs
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*Arthritis, posterior paresis and ill-thrift
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*Microscopic identification of bacteria in pus and isolation of ''S. aureus''
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*Prophylactic antibiotics e.g. tetracyclines initiated at 1 week of age may prevent infection
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*Tick control important
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===Exudative epidermitis ([[Bacterial skin infections - Pathology#Greasy pig disease|Greasy pig disease]])===
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*Worldwide disease of pigs under 3 months of age caused by ''S. hyicus''
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*Highly contagious and persists in the environment for long periods
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*''S. hyicus'' produces exfoliative toxin that causes separation of cells in stratum spinosum resulting in rapid intraepidermal spread of organisms
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*Similar to “scalded skin syndrome” in human neonates, due to skin infection by exfoliative toxin-producing ''Staphylococcus aureus''
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*Excessive sebacious secretion and exudation on surface of skin
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*Pigs are anorexic, febrile, depressed and have a greasy, non-pruritic dermatitis
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*SKin thickened, wrinkled and scaley
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*Acute death in piglets under 3 weeks due to dehydration and septicaemia
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*20-100% morbidity; up to 90% mortality
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*Organism enters skin via abrasions e.g. bite wounds
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*Carried in vaginal mucosa and skin of sows
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*Predisposed by lack of milk, weaning and other infections
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*Piglets from non-immune sows are predisposed
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*Passive transfer of antibodies from immune sows and development of immunity with age protect against disease
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*Isolation from skin lesions
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*Early systemic antibiotics amd topical antiseptics/antibiotics useful
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*Disinfection after outbreak
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*Wash sows before farrowing
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*Differential diagnosis:
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**Mange (''Sarcoptes scabiei var. suis'')
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**Swine parakeratosis (zinc and essential fatty acid deficiency)
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**Porcine juvenile pustular psoriasiform dermatitis (collarettes or rings typically on the ventrum of young pigs)
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**Dermatosis vegetans (associated with a giant cell pneumonia)
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**Dermatophytosis (most commonly ''Microsporum nanum'')
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===[[Muscles Inflammatory - Pathology#Botryomycosis|Botryomycosis]]===
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*Chronic, suppurative granulomatous condition
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*''S. aureus''
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*Occurs following castration of horses due to infection of stump of spermatic cors
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*Occurs in mammary tissues of sows
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*Mass of fibrous tissue containing pus and sinus tracts
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===Infections in dogs and cats===
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*''S. intermedius'' causes [[Bacterial skin infections - Pathology#Deep pyoderma|deep pyoderma]], otitis externa, mastitis, endometritis, cystitis, osteomyelitis, wound infections, [[Joints Inflammatory - Pathology#In Dogs|dyscospondylitis]]
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*''S. aureus'' may cause [[Intestines - disease due to pathogens#Staphylococcus|gastroenteritis]]
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===Other infections caused by ''S. aureus''===
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*[[Bacterial skin infections - Pathology#Impetigo|Impetigo]] in cattle and pigs
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* [[General Pathology - Oedema#Permeability type|Permeability types of pulmonary oedema]]
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*Haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]]
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*May infect [[Joints Inflammatory - Pathology#In Sheep|joints of sheep]]; [[Joints Inflammatory - Pathology#In Pigs|arthritis in pigs]]
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*Dermatitis in sheep and goats
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*Arthritis and septicaemia in turkeys
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*Bumblefoot and omphalitis in chickens
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===Coagulase-negative staphylococci===
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*Usually harmless commensals or secondary invaders
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*May adhere to indwelling catheters leading to urinary tract infections
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*Often display multiple antibiotic resistance
 
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