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Questions and Answers
Which term describes the presence of viable bacteria in the blood, regardless of symptoms?
Which term describes the presence of viable bacteria in the blood, regardless of symptoms?
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What is the primary method for diagnosing sepsis?
What is the primary method for diagnosing sepsis?
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Which Staphylococcus species is coagulase-positive?
Which Staphylococcus species is coagulase-positive?
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Which enzyme produced by Staphylococci inactivates toxic hydrogen peroxide?
Which enzyme produced by Staphylococci inactivates toxic hydrogen peroxide?
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Which toxin causes scalded skin syndrome in neonates?
Which toxin causes scalded skin syndrome in neonates?
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What is the arrangement of Staphylococcus aureus under a microscope?
What is the arrangement of Staphylococcus aureus under a microscope?
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Which test differentiates Staphylococci (catalase-positive) from Streptococci (catalase-negative)?
Which test differentiates Staphylococci (catalase-positive) from Streptococci (catalase-negative)?
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Which Staphylococcus species is a common cause of urinary tract infections in young females?
Which Staphylococcus species is a common cause of urinary tract infections in young females?
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Which of the following is NOT a toxogenic disease caused by S. aureus?
Which of the following is NOT a toxogenic disease caused by S. aureus?
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Which term describes the presence and multiplication of bacteria in the blood?
Which term describes the presence and multiplication of bacteria in the blood?
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A patient presents with fever, hypotension, and desquamation of the skin. They recently used tampons. What is the most likely diagnosis and causative agent?
A patient presents with fever, hypotension, and desquamation of the skin. They recently used tampons. What is the most likely diagnosis and causative agent?
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A blood culture taken from a patient 48 hours after hospital admission grows Staphylococcus epidermidis. How would you classify this bloodstream infection?
A blood culture taken from a patient 48 hours after hospital admission grows Staphylococcus epidermidis. How would you classify this bloodstream infection?
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A patient with infective endocarditis has persistent bacteria in their blood. What type of bacteremia is this?
A patient with infective endocarditis has persistent bacteria in their blood. What type of bacteremia is this?
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Why does S. aureus cause beta-hemolysis on blood agar?
Why does S. aureus cause beta-hemolysis on blood agar?
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Which virulence factor of S. aureus helps it evade phagocytosis by binding to the Fc portion of IgG?
Which virulence factor of S. aureus helps it evade phagocytosis by binding to the Fc portion of IgG?
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A patient develops a bloodstream infection after undergoing a dental procedure. What is the most likely classification of this infection based on its origin?
A patient develops a bloodstream infection after undergoing a dental procedure. What is the most likely classification of this infection based on its origin?
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Which of the following statements about Staphylococci is FALSE?
Which of the following statements about Staphylococci is FALSE?
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A patient with pneumonia develops a bloodstream infection. The blood culture is positive for Streptococcus pneumoniae. How would you classify this bloodstream infection?
A patient with pneumonia develops a bloodstream infection. The blood culture is positive for Streptococcus pneumoniae. How would you classify this bloodstream infection?
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Which of the following is NOT a characteristic of enterotoxins produced by S. aureus?
Which of the following is NOT a characteristic of enterotoxins produced by S. aureus?
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Which of the following statements regarding S. epidermidis is TRUE?
Which of the following statements regarding S. epidermidis is TRUE?
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A Gram stain of a pus sample shows Gram-positive cocci in clusters. Which of the following organisms is most likely responsible for the infection?
A Gram stain of a pus sample shows Gram-positive cocci in clusters. Which of the following organisms is most likely responsible for the infection?
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Which of the following is a selective medium used to isolate S. aureus?
Which of the following is a selective medium used to isolate S. aureus?
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A patient presents with fever, chills, and positive blood cultures. The causative organism is identified as Escherichia coli. How would you classify this bloodstream infection based on the causative agent?
A patient presents with fever, chills, and positive blood cultures. The causative organism is identified as Escherichia coli. How would you classify this bloodstream infection based on the causative agent?
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Which of the following is NOT a typical specimen collected for the laboratory diagnosis of S. aureus infections?
Which of the following is NOT a typical specimen collected for the laboratory diagnosis of S. aureus infections?
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Which of the following statements about MRSA is TRUE?
Which of the following statements about MRSA is TRUE?
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Study Notes
Blood Stream Infections: Key Concepts
- Bacteremia: Presence of viable bacteria in the bloodstream without necessarily causing symptoms.
- Septicemia: Presence and multiplication of bacteria in the blood, often leading to systemic illness.
- Toxemia: Presence of toxins in the blood.
Diagnostic Methods
- Sepsis Diagnosis: Primary method is blood culture, which identifies pathogens in the bloodstream.
- Catalase Test: Differentiates Staphylococci (catalase-positive) from Streptococci (catalase-negative).
Staphylococcus Overview
- Coagulase-Positive Species: Staphylococcus aureus is coagulase-positive, while S. epidermidis and S. saprophyticus are coagulase-negative.
- Enzyme Function: Catalase produced by Staphylococci inactivates hydrogen peroxide, allowing survival in the presence of oxygen.
Pathogenic Mechanisms
- Scalded Skin Syndrome: Caused by exfoliative toxin, primarily affecting neonates.
- Beta-Hemolysis: S. aureus causes this on blood agar due to membrane-damaging toxins.
Clinical Scenarios and Infections
- Toxic Shock Syndrome: Often related to tampon use and can result in fever, hypotension, and skin desquamation, primarily caused by S. aureus.
- Nosocomial Infections: Blood culture growing Staphylococcus epidermidis indicates a hospital-acquired infection.
Types of Bacteremia
- Persistent Bacteremia: Associated with conditions like infective endocarditis, classified as continuous bacteremia.
- Dental Procedures: Can lead to secondary bacteremia due to transient bacteria entering the bloodstream.
Staphylococcus Characteristics
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Virulence Factors:
- Protein A helps evade phagocytosis by binding to IgG.
- Capsules and coagulase enhance pathogenicity.
- False Statement About Staphylococci: Not all species are coagulase-positive; only S. aureus is.
Infection Classification
- Primary vs. Secondary Bacteremia: Primary infections arise from a primary site, while secondary infections occur due to bacteremia from another infected area.
- Community vs. Nosocomial: Infections can be community-acquired or associated with healthcare settings.
Organism Identification
- Gram Staining: Pus samples showing Gram-positive cocci in clusters most likely indicate S. aureus.
- Isolation Medium: Mannitol salt agar is a selective medium for isolating S. aureus, differentiating it from other bacteria.
E. coli Infections
- Bloodstream infections caused by E. coli are classified as Gram-negative due to its cell wall characteristics.
MRSA (Methicillin-Resistant Staphylococcus aureus)
- Resistant Strain: MRSA is known for its resistance to methicillin and often shows multiple drug resistance, yet can still be treated with vancomycin.
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