7.4 Staphylococcus aureus

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Figure 15 Staphylococcus aureus is a Gram-positive, aerobic coccus which tends to form grape-like clusters, with each bacterium being up to 1 μm in diameter
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An image of Staphylococcus aureus.

Figure 15 Staphylococcus aureus is a Gram-positive, aerobic coccus which tends to form grape-like clusters, with each bacterium being up ...

What are the main characteristics of S. aureus?

Answer

S. aureus belongs to the genus Staphylococcus. It is a Gram-positive, catalase-positive and coagulase-positive aerobic coccus, although the capacity to produce coagulase enzyme may be weak in some strains.

S. aureus is included in the list of priority pathogens for AMR surveillance since many lineages carry genes that confer resistance to virtually all the beta-lactam antimicrobials: the methicillin-resistant Staphylococcus aureus (MRSA) strains. S. aureus is a frequent pathogen of humans and MRSA are a particular threat in healthcare settings.

MRSA are less problematic in veterinary medicine as infections with such strains are not very prevalent. However, methicillin-susceptible S. aureus (MSSA) strains cause a range of infections in production animal species, including:

  • contagious mastitis in farmed ruminants
  • sporadic or endemic skin infections in all animals
  • sporadic wound, soft tissue and bone infections in all animals
  • endemic joint infections in poultry.

Despite some worrisome documented evolutionary host-jumps from livestock to humans, transmission of S. aureus from farm animals to humans is not common and usually, S. aureus is not considered a zoonotic agent. Moreover, comparative genomic analyses of human and animal strains indicate that humans and livestock are generally infected with host-specialised lineages that tend to remain confined within their host-niche.

7.3.1 Isolation of Salmonella

7.4.1 Isolation of S. aureus