Microbiology Chapter on Staphylococcus aureus

Which of the following is true regarding S. aureus?

S. epidermidis is a coagulase-positive staphylococcus.

What is one of the morphological characteristics of Staphylococcus aureus?

The ability to produce staphylocoagulase distinguishes ___________ from coagulase-negative staphylococci.

Match the following terms with their descriptions:

What is the primary shape of Staphylococcus aureus bacteria?

S. aureus can ferment mannitol, resulting in yellow colonies on mannitol salt agar.

Name a virulence factor of Staphylococcus aureus that protects it from immune defenses.

S. aureus is classified as a __________ anaerobe.

Match the following media with their characteristics regarding S. aureus:

Morphology

Staphylococcus aureus strains, like other staphylococci, are Gram-positive spherical cocci (about 1 μm in diameter) occurring in irregular grape-like clusters.

Cultural Characters

S. aureus is a facultative anaerobe.
It usually grows on:
- Nutrient agar.
- Blood agar, producing complete (β-) hemolysis due to production of hemolysins.
- Mannitol salt agar (selective indicator medium) producing yellow colonies due to mannitol fermentation. This medium facilitates isolation of S. aureus (salt tolerant) from specimens contaminated by other bacteria.

Virulence Factors and Pathogenesis

Staphylocoagulase: Coagulase is an extracellular protein that has the ability to convert plasma fibrinogen to fibrin. By this mechanism, a fibrin barrier is formed.
- This leads to:
  - Protection from phagocytic and immune defenses.
  - Localization of infection (e.g., furuncles).
The clumping factor (fibrogen-binding protein): This is an important adhesin that leads to attachment of the organism to traumatized tissue and blood clots.
Invins: Leuocidin, staphylokinase and hyaluronidase promote bacterial spread in tissues.
Protein A: It is present on the surface of S. aureus. It binds non-specifically to the Fc portion of IgG leading to inhibition of opsonization.
Hemolysins (e.g., alpha toxin): These are pore-forming toxins that lyse host cell membranes.
Exotoxins having superantigen mechanism (see vol. I):
- Enterotoxins: responsible for staphylococcal food poisoning.
- Toxic shock syndrome toxin-1 (TSST-1):
- Epidermolytic (exfoliatin) toxins: responsible for staphylococcal scaled skin syndrome (SSSS).

This quiz focuses on the morphology, cultural characteristics, and virulence factors of Staphylococcus aureus. It explores its growth conditions, hemolytic properties, and mechanisms of pathogenesis, making it essential for microbiology students to understand this important bacterium.