Questions and Answers
What is the primary criterion of pathogenicity for Staphylococcus aureus?
Which specimen type is considered the best sample for laboratory diagnosis of Staphylococcus aureus?
What is the interpretation of a zone diameter of 15 mm in antibiotic susceptibility testing for Staphylococcus aureus?
Which of the following tests is used to detect cell bound coagulase in Staphylococcus aureus?
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How does Staphylococcus saprophyticus differ from other Coagulase-Negative Staphylococci (CoNS)?
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Which species is associated with green hemolysis around the colony?
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Which of the following describes beta-hemolytic Streptococci?
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Which Streptococcus species is NOT mentioned as beta-hemolytic?
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What type of hemolysis is displayed by Streptococcus aureus?
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Which species is correctly associated with the alpha-hemolytic result?
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What is the primary purpose of the catalase test?
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What indicates a positive result in the tube coagulase test after incubation?
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Which component of the cooperative action is formed during the reaction of coagulase with coagulase-reacting factor?
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What does a yellow color indicate in the mannitol fermentation test?
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Which of the following organisms is likely to produce a positive coagulase test?
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Which enzyme catalyzes the decomposition of H2O2 into water and oxygen?
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What type of coagulase is bound to a cell?
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What is the primary purpose of the Mannitol Fermentation Test?
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What type of hemolysin is associated with enhanced activity at different temperatures, specifically mentioned as 'hot-cold' lysin?
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Which of the following toxins is categorized as a superantigen and causes the epidermal layer of the skin to slough off?
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What characteristic makes Staphylococcus lugdunensis more aggressive compared to other coagulase-negative staphylococci?
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Which of the following is NOT true regarding the antimicrobial test results for coagulase-negative staphylococci?
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What does Toxic Shock Syndrome Toxin-1 stimulate in the body?
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Which hemolysin is associated with the destruction of red blood cells and is linked to Panton-Valentine leukocidin?
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What is the significance of a urine culture showing 10,000 CFU/mL?
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What specific characteristic is tested to differentiate S. saprophyticus from other coagulase-negative staphylococci?
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What medium is used to test for esculin hydrolysis in Group D Streptococci?
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What does a positive result for esculin hydrolysis indicate?
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Which species is NOT classified as an Enterococcus?
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What is a characteristic reaction exhibited by Group D Streptococci in a catalase test?
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What is a common virulence factor among Group D Streptococci?
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Study Notes
Enzymes and Toxins Produced (Virulence Factors)
- Coagulase: Major virulence factor; coagulates fibrinogen in plasma, forming a protective fibrin layer around staphylococcal abscesses.
- Catalase: Heme enzyme that decomposes hydrogen peroxide (H2O2) into water and oxygen; distinguishes staphylococci (+) from streptococci (-).
- Mannitol Fermentation Test: Differentiates pathogenic from non-pathogenic staphylococci; Staphylococcus aureus ferments mannitol, producing a yellow color.
- Beta Hemolysin: Enhances hemolytic activity; requires incubation at 37ºC followed by exposure to 4ºC.
- Delta Hemolysin: Associated with the destruction of red blood cells; linked to Panton-Valentine Leukocidin.
- Exfoliatin A and B: Superantigens that cause epidermal shedding, leading to scalded skin syndrome.
- Toxic Shock Syndrome Toxin-1 (TSST-1): Chromosomal-mediated toxin causing menstruation-associated toxic shock syndrome (TSS); stimulates cytokine production.
Coagulase and Catalase Tests
- Tub Method: Sensitive method for detecting free coagulase; clot formation after 1-4 hours indicates a positive result.
- Aerobic Catalase Test: Uses 3% H2O2; identifies differences between staphylococci and streptococci.
- Anaerobic Catalase Test: Employs 15% H2O2; confirms catalase production in anaerobic conditions.
Staphylococcus Differentiation
- Two types of coagulase:
- Cell-bound Coagulase: Attached to the cell wall.
- Free Coagulase: Detected in tube methods.
- Mannitol Salt Agar (MSA): Contains 1% mannitol, 7.5% NaCl, and phenol red as a pH indicator; the presence of yellow colonies indicates mannitol fermentation by S. aureus.
- Novobiocin Susceptibility Test: Differentiates S. saprophyticus (resistant) from other coagulase-negative staphylococci (sensitive); zone diameter interpretation (S: >16 mm; R: ≤16 mm).
Laboratory Diagnosis
- Specimens: Best samples include aspirated secretions and purulent exudates; joint fluids may also be tested.
- Gram Stain: Identifies gram-positive spherical cells; positive results indicate S. lugdunensis, S. intermedius, S. schleiferi (green hemolysis) or negative for S. aureus.
- Bile Esculin Medium: Tests for esculin hydrolysis; (+) result is a black color in agar within 48 hours, indicating Group D enterococci.
Enterococci vs. Non-Enterococci
- Family: Streptococcaceae; previously classified as Group D Streptococci.
- Natural Habitat: Intestinal tracts of humans and animals; exhibit weak bubbling in catalase tests (pseudocatalase).
- Resistance: Resistant to multiple antimicrobial agents; may display α, β, or non-hemolytic patterns.
- Virulence Factors: Include extracellular serine protease, gelatinase, and cytolysin.
- Species: Comprise E. faecalis, E. faecium, E. avium, E. gallinarum, E. durans, among others.
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Description
This quiz focuses on the virulence factors produced by the Schleiferi, particularly enzymes and toxins. It covers the tube method for detecting coagulase, as well as the catalase enzyme's role in decomposing hydrogen peroxide. Test your understanding of these critical microbiological concepts.
