Staphylococcus aureus

Overview

Staphylococcus aureus is a species of major veterinary significance as it can infect most of the common domestic species. Though transfer between species and between animals and man is limited there is still significant levels of S. aureus existing in the environment to pose a threat if not properly controlled. It is a major cause of mastitis in cattle, sheep, goats and horses.

Characteristics

S. aureus has a standard staphylococcal morphology but varies somewhat in its biochemistry.

Bovine mastitis

S. aureus is a common cause of mastitis in 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

Tick pyaemia

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

Botryomycosis

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

Other infections caused by S. aureus

Impetigo in cattle and pigs
Permeability types of pulmonary oedema
Haemorrhagic disease by secondary thrombocytopenic disease
May infect joints of sheep; arthritis in pigs
Dermatitis in sheep and goats
Arthritis and septicaemia in turkeys
Bumblefoot and omphalitis in chickens