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 cord
• 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

• 30% strains of Staphylococcus aureus produce potent enterotoxin. T
  • Protein and heat-stable
  • Responsible for staphylococcal food poisoning in man.
• Every reason to assume that acute gastro-intestinal disturbance in small animals may be caused by these enterotoxins BUT not well documented.
• Symptoms last 24-36 hours and include:
  • Acute vomiting
  • Diarrhoea
  • Pain
• The enterotoxins are superantigens.
  • Induce release of cytokines from lymphocytes