Difference between revisions of "Staphylococcus spp."

Revision as of 16:07, 20 July 2008

Commensals on skin and mucous membranes of animals and man
Enodgenous or exogenous infections
Opportunistic pyogenic infections associated with trauma, immusuppression, other infections
Coagulase-positive S. aureus and S. intermedius as well as S. hyicus are important pathogens of animals
Fairly stable in environment
Strains selective for particular species
Cause mastitis, tick pyaemia, exudative epidermitis, botryomycosis and pyoderma

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; free coagulase converts prothrombin to thrombin which converts fibrinogen to fibrin
Biochemical tests to differentiate S. aureus and S. intermedius
PCR to differentiate species

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

S. aureus is a common cause of mastitisin cattle worldwide
Most infections subclinical
Systemic infection can occur with peracute and gangrenous forms
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

Infection of lambs with S. aureus in hill-grazing areas of the UK
Lambs carry S. aureus on their skin and nasal mucosa; infection via skin trauma including tick bites
Ixodes ricinus tick acts as a vector for Ehrlichia phagocytophila, which causes immunosuppression in lambs, predisposing to staphylococcal infection
Acute septicaemia and death or localised abscess formation in many organs
Arthritis, posterior paresis and ill-thrift
Microscopic identification of bacteria in pus and isolation of S. aureus
Prophylactic antibiotics e.g. tetracyclines initiated at 1 week of age may prevent infection
Tick control important

Worldwide disease of pigs under 3 months of age caused by S. hyicus
Highly contagious and persists in the environment for long periods
S. hyicus produces exfoliative toxin that causes separation of cells in stratum spinosum resulting in rapid intraepidermal spread of organisms
Similar to “scalded skin syndrome” in human neonates, due to skin infection by exfoliative toxin-producing Staphylococcus aureus
Excessive sebacious secretion and exudation on surface of skin
Pigs are anorexic, febrile, depressed and have a greasy, non-pruritic dermatitis
Acute death in piglets under 3 weeks due to dehydration and septicaemia
20-100% morbidity; up to 90% mortality
Organism enters skin via abrasions e.g. bite wounds
Carried in vaginal mucosa and skin of sows
Predisposed by lack of milk, weaning and other infections
Piglets from non-immune sows are predisposed
Passive transfer of antibodies from immune sows and development of immunity with age protect against disease
Isolation from skin lesions
Early systemic antibiotics amd topical antiseptics/antibiotics useful
Disinfection after outbreak
Wash sows before farrowing
Differential diagnosis:
- Mange (Sarcoptes scabiei var. suis)
- Swine parakeratosis (zinc and essential fatty acid deficiency)
- Porcine juvenile pustular psoriasiform dermatitis (collarettes or rings typically on the ventrum of young pigs)
- Dermatosis vegetans (associated with a giant cell pneumonia)
- Dermatophytosis (most commonly Microsporum nanum)

Chronic, suppurative granulomatous condition
S. aureus
Occurs following castration of horses due to infection of stump of spermatic cors
Occurs in mammary tissues of sows
Mass of fibrous tissue containing pus and sinus tracts

S. intermedius causes deep pyoderma, otitis externa, mastitis, endometritis, cystitis, osteomyelitis, wound infections, dyscospondylitis
S. aureus may cause gastroenteritis

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 *Cell wall proteins bind fibronectin and fibrinogen, allowing bacteria to attched to damaged tissues
 *Coagulase, DNase and protein A production mark pathogenicity
+*
 ===Diagnosis===