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Questions and Answers
Which of the following is true regarding S. aureus?
Which of the following is true regarding S. aureus?
- It produces opaque, non-pigmented colonies.
- It is a Gram-negative bacterium.
- It is the most pathogenic species in the Staphylococcus genus. (correct)
- It is coagulase-negative.
S. epidermidis is a coagulase-positive staphylococcus.
S. epidermidis is a coagulase-positive staphylococcus.
False (B)
What is one of the morphological characteristics of Staphylococcus aureus?
What is one of the morphological characteristics of Staphylococcus aureus?
Gram-positive spherical cocci in grape-like clusters
The ability to produce staphylocoagulase distinguishes ___________ from coagulase-negative staphylococci.
The ability to produce staphylocoagulase distinguishes ___________ from coagulase-negative staphylococci.
Match the following terms with their descriptions:
Match the following terms with their descriptions:
What is the primary shape of Staphylococcus aureus bacteria?
What is the primary shape of Staphylococcus aureus bacteria?
S. aureus can ferment mannitol, resulting in yellow colonies on mannitol salt agar.
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.
Name a virulence factor of Staphylococcus aureus that protects it from immune defenses.
S. aureus is classified as a __________ anaerobe.
S. aureus is classified as a __________ anaerobe.
Match the following media with their characteristics regarding S. aureus:
Match the following media with their characteristics regarding S. aureus:
Flashcards
Staphylococcus
Staphylococcus
A genus of bacteria characterized by gram-positive, spherical cocci arranged in grape-like clusters, catalase-positive, and producing opaque, pigmented colonies on agar.
Staphylocoagulase
Staphylocoagulase
An enzyme produced by S. aureus that clots plasma and is used to distinguish it from coagulase-negative staphylococci.
Staphylococcus aureus
Staphylococcus aureus
The most pathogenic species of Staphylococcus, known for causing a wide range of infections.
Coagulase-negative staphylococci
Coagulase-negative staphylococci
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Morphology of Staphylococcus
Morphology of Staphylococcus
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What is the morphology of Staphylococcus aureus?
What is the morphology of Staphylococcus aureus?
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What is the oxygen requirement of S. aureus?
What is the oxygen requirement of S. aureus?
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What color are S. aureus colonies on nutrient agar?
What color are S. aureus colonies on nutrient agar?
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What types of media do S. aureus grow on and their respective characteristics?
What types of media do S. aureus grow on and their respective characteristics?
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What is the function of coagulase in S. aureus and its effects on infection?
What is the function of coagulase in S. aureus and its effects on infection?
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Study Notes
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).
- This leads to:
- 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).
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