Category:Staphylococcus species

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Overview

  • 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

Characteristics

  • 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
  • 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

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
  • Haemolysins made by S. aureus and S. intermedius act as toxins
  • Alpha-haemolysin prouces a narrow zone of complete haemolysis; this toxin causes necrosis and targets mast cells and plasma cells, whose contents cause damage
  • Beta-haemolysin produces a wide zone of incomplete haemolysis; damages membranes and causes leakage, contributing to necrosis
  • Also gamma and delta toxins
  • 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
  • Enterotoxins produced by some strains of S. aureus cause food poisoning in humans
  • Proteases, hyaluronidases and lipases facilitate survival of bacteria and spread and tissue destruction

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

Infections in dogs and cats

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

Coagulase-negative staphylococci

  • Usually harmless commensals or secondary invaders
  • May adhere to indwelling catheters leading to urinary tract infections
  • Often display multiple antibiotic resistance

Enteritis

  • 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

Pages in category "Staphylococcus species"

The following 3 pages are in this category, out of 3 total.