Staphylococcal Infections Overview

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Questions and Answers

What is a primary characteristic of teichoic acids in Staphylococci?

  • They enhance nutrient absorption for the bacteria.
  • They are highly immunogenic.
  • They contribute to the rigidity of the cell wall. (correct)
  • They are found only in Staphylococcus aureus.

How do capsule-deficient mutants of Staphylococci compare to their encapsulated counterparts?

  • They have improved immune evasion capabilities.
  • They contribute more to chronic infections.
  • They are more likely to form biofilms.
  • They are less virulent and more easily phagocytosed. (correct)

What role does Protein A play in Staphylococcal infections?

  • It binds the Fc region of IgG, aiding immune evasion. (correct)
  • It helps in the formation of biofilms.
  • It activates complement pathways.
  • It strengthens the cell wall.

Which of the following enzymes produced by Staphylococci enhances infection by degrading host components?

<p>Coagulase (A)</p> Signup and view all the answers

What is the function of alpha-toxin in Staphylococcus pathogenicity?

<p>It is a pore-forming toxin toxic to various cell types. (A)</p> Signup and view all the answers

Which species of Staphylococci is notably mentioned as proficient in biofilm formation?

<p>Staphylococcus epidermidis (D)</p> Signup and view all the answers

Which of the following toxins is specifically associated with Staphylococcal Scalded Skin Syndrome (SSSS)?

<p>Exfoliative Toxins ETA and ETB (A)</p> Signup and view all the answers

What is one effect of Staphylococcal virulence factors on B-cells?

<p>They induce apoptosis in B-cells. (B)</p> Signup and view all the answers

Which statement about the pathogenicity of Staphylococcus aureus is accurate?

<p>It is associated with a range of clinical manifestations including septic arthritis. (D)</p> Signup and view all the answers

During which growth phase does Staphylococcus prioritize the expression of cell-surface factors?

<p>During exponential growth phase (B)</p> Signup and view all the answers

How does the agr system regulate virulence factor expression in Staphylococcus?

<p>Based on cell density via quorum sensing (D)</p> Signup and view all the answers

What is a common characteristic of coagulase-negative staphylococci regarding their virulence?

<p>They are less virulent but proficient biofilm formers. (B)</p> Signup and view all the answers

Which feature characterizes enterotoxins produced by Staphylococcus?

<p>They are involved in food poisoning and are heat-stable. (A)</p> Signup and view all the answers

What is the role of Superantigens like Toxic Shock Syndrome Toxin (TSST-1)?

<p>They hyperstimulate the immune system by binding to MHC II and T cell receptors. (D)</p> Signup and view all the answers

Which statement is true regarding the expression of toxins at low and high cell density according to the agr system?

<p>At low cell density, surface proteins are expressed while toxins are downregulated. (B)</p> Signup and view all the answers

What is the main characteristic of delta-toxin in Staphylococcus?

<p>It is a membrane-disrupting, nonspecific toxin. (C)</p> Signup and view all the answers

Which form of staphylococcal infection is characterized by desquamation, primarily in neonates and young children?

<p>Staphylococcal Scalded Skin Syndrome (SSSS) (B)</p> Signup and view all the answers

What is a common cause of bacteremia and endocarditis, particularly among intravenous drug users?

<p>Staphylococcus aureus (A)</p> Signup and view all the answers

Which condition is primarily caused by ingestion of enterotoxin-laden foods?

<p>Staphylococcal Food Poisoning (B)</p> Signup and view all the answers

What serious respiratory condition can result from staphylococcal infection due to inhalation or hematogenous spread?

<p>Empyema (D)</p> Signup and view all the answers

Which syndrome is often linked to tampon use in menstruating women and is caused by TSST-1?

<p>Toxic Shock Syndrome (A)</p> Signup and view all the answers

Which staphylococcal infection is NOT typically classified as an invasive infection?

<p>Impetigo (D)</p> Signup and view all the answers

What is a critical challenge in managing staphylococcal infections?

<p>Limited treatment options due to evolving antibiotic resistance (A)</p> Signup and view all the answers

Which of the following conditions is characterized by severe necrotizing pneumonia related to staphylococcal infections?

<p>Pneumonia and Empyema (A)</p> Signup and view all the answers

Flashcards

Staphylococcal virulence factors

Mechanisms that Staphylococcus aureus uses to cause disease, including toxins and regulated expression.

Cytotoxins

Staphylococcus toxins that damage cells.

Alpha-toxin

A pore-forming cytotoxin that damages various cell types.

Exfoliative Toxins (ETA/ETB)

Serine proteases that cause Staphylococcal Scalded Skin Syndrome (SSSS).

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Superantigens

Toxins that overstimulate the immune system, causing TSS (Toxic Shock Syndrome).

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Agr System

Quorum sensing system regulating virulence factor expression based on cell density.

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Temporal Expression of Virulence Factors

Virulence factors are expressed in a specific order throughout bacterial growth.

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Cell-surface factors

Factors involved in staphylococcus adherence and colonization

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Staphylococcus aureus

A type of Gram-positive bacteria that causes many human infections

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Teichoic acids

Important cell wall components of Staphylococci, making up a large portion of the bacteria's dry weight.

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Capsule (Staphylococcus)

Polysaccharide layer surrounding some Staphylococci, helping them avoid immune cells

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Protein A (Spa)

A Staphylococcal protein that interferes with the immune response

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Virulence enzymes

Staphylococcal enzymes that break down host tissues, helping bacteria spread

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Biofilms

Communities of bacteria, often resistant to treatment, formed by some Staphylococcus species

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Staphylococcus cell wall

Its structure includes important components like teichoic acids, impacting the bacteria's pathogenicity

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Staphylococcus infections

Variety of infections caused by Staphylococci, impacting humans and animals

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Staphylococcal Skin Infections

Common skin infections like impetigo, folliculitis, furuncles, carbuncles, and wound infections.

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Staphylococcal Bacteremia and Endocarditis

Blood infection (bacteremia) and heart infection (endocarditis) caused by S. aureus, often severe, especially for IV drug users.

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Staphylococcal Pneumonia and Empyema

Lung infection (pneumonia) and pus-filled chest cavity (empyema) caused by S. aureus, possibly from inhaled or bloodstream spread.

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Staphylococcal Osteomyelitis and Septic Arthritis

Bone infection (osteomyelitis) and joint infection (septic arthritis) often caused by S. aureus, needing immediate treatment.

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Staphylococcal Scalded Skin Syndrome (SSSS)

Skin peeling syndrome, mostly affecting newborns and young children, due to staphylococcal toxins.

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Staphylococcal Food Poisoning

Gastrointestinal illness caused by eating food contaminated with S. aureus toxins.

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Toxic Shock Syndrome

Systemic illness caused by toxins (TSST-1) from S. aureus, sometimes tied to tampon use.

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Staphylococcal Virulence Mechanisms

The ways S. aureus causes disease, critical for treatment and prevention.

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Study Notes

Staphylococcal Infections and Virulence

  • Staphylococci are Gram-positive bacteria causing various human infections.
  • The document focuses on Staphylococcus aureus.
  • Staphylococci are facultative anaerobes found on human skin and mucous membranes.

Physiology and Structure

  • Cell Wall Components:
    • Teichoic Acids: Species-specific, comprise 30-50% of the cell wall's dry weight, contribute to rigidity and pathogenicity. Poor immunogens.
    • Capsule: Composed of polysaccharides. Clinically significant serotypes are 5 and 8.

Protein A (Spa)

  • Functions:
    • Immune evasion by binding IgG, preventing neutrophil binding.
    • Acts as a B-cell superantigen (binding IgM), causing apoptosis.
  • Clinical Relevance: A virulence factor in septic arthritis and murine pneumonia.

Enzymes (Virulence Enzymes)

  • Staphylococcal enzymes like β-lactamase, catalase, coagulase, V8 protease, and staphopain degrade host components, enhancing infection and providing nutrients.

Biofilms

  • S. epidermidis and other coagulase-negative staphylococci are less toxigenic but proficient biofilm formers, causing chronic infections.

Toxins (Cytotoxins)

  • Alpha-toxin (Hla): Pore-forming, toxic to various cell types.
  • Beta-toxin: Sphingomyelinase C, specific for sphingomyelin.
  • Delta-toxin: Membrane-disrupting, non-specific.
  • Gamma-toxin and PVL (Panton-Valentine Leukocidin): Bi-component toxins, beta-barrel structure.

Exfoliative Toxins

  • ETA and ETB: Serine proteases causing Staphylococcal Scalded Skin Syndrome (SSSS) by degrading desmosomes.

Superantigens

  • Toxic Shock Syndrome Toxin (TSST-1): Hyperstimulates the immune system, binding to MHC II molecules and T cell receptors, causing Toxic Shock Syndrome (TSS).

Enterotoxins

  • Causes food poisoning; heat-stable; encoded on various SaPls.

Temporal Expression

  • During exponential growth, expression of cell-surface factors is prioritized.
  • Post-exponential phase, the expression of cell-surface genes are repressed, while extracellular toxin genes are activated.

Agr System

  • Uses quorum sensing to regulate virulence factors based on cell density.
  • At low cell density, surface proteins are expressed, and toxins are downregulated.
  • At high cell density, surface proteins are downregulated, and toxins are expressed.

Clinical Manifestations

  • Skin Infections: Impetigo, folliculitis, furuncles, carbuncles, and wound infections.
  • Invasive Infections:
    • Bacteremia and Endocarditis: S. aureus is a common cause, with high mortality, especially in intravenous drug users.
    • Pneumonia and Empyema: Caused by inhalation or hematogenous spread, leading to severe conditions like necrotizing pneumonia.
    • Osteomyelitis and Septic Arthritis: S. aureus is the predominant cause, requiring immediate treatment.
  • Toxin-Mediated Syndromes:
    • Staphylococcal Scalded Skin Syndrome (SSSS)
    • Staphylococcal Food Poisoning
    • Toxic Shock Syndrome

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