Staphylococcus aureus Identification and Properties
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Questions and Answers

A lab tech reports gram-positive cocci in clusters from a blood culture. Which result most strongly indicates that Staphylococcus aureus is present?

  • Growth in only one of two blood samples.
  • Coagulase-negative result.
  • Growth of _Staphylococcus epidermidis_.
  • Coagulase-positive result. (correct)

A single positive blood culture for Staphylococcus epidermidis always indicates bacteremia.

False (B)

What enzyme produced by Staphylococcus aureus activates prothrombin, leading to blood clot formation?

coagulase

If a lab identifies coagulase-negative, gram-positive cocci in clusters, consider Staphylococcus epidermidis or Staphylococcus ______.

<p>saprophyticus</p> Signup and view all the answers

Match the Staphylococcus species with their characteristic.

<p><em>Staphylococcus aureus</em> = Coagulase-positive <em>Staphylococcus epidermidis</em> = Often a skin contaminant in blood cultures <em>Staphylococcus saprophyticus</em> = Coagulase-negative</p> Signup and view all the answers

What characteristic of Staphylococcus epidermidis facilitates its adherence to prosthetic materials?

<p>A polysaccharide capsule. (D)</p> Signup and view all the answers

The likelihood of bacteremia with Staphylococcus epidermidis is low when two cultures test positive.

<p>False (B)</p> Signup and view all the answers

Name the Staphylococcus aureus exotoxin responsible for scalded skin syndrome.

<p>Exfoliatin</p> Signup and view all the answers

Staphylococcus aureus has a ______ surrounding its huge peptidoglycan cell wall.

<p>microcapsule</p> Signup and view all the answers

Match the Staphylococcus aureus exotoxin with its associated effect.

<p>Exfoliatin = Causes scalded skin syndrome Enterotoxins = Causes food poisoning, resulting in vomiting and diarrhea Toxic Shock Syndrome Toxin (TSST-1) = Induces toxic shock syndrome</p> Signup and view all the answers

Which mechanism does Protein A employ to protect Staphylococcus aureus from opsonization and phagocytosis?

<p>Binding to the Fc region of IgG antibodies. (B)</p> Signup and view all the answers

Coagulase protects bacteria from phagocytosis by directly neutralizing the reactive oxygen species produced by phagocytes.

<p>False (B)</p> Signup and view all the answers

What is the primary mechanism by which superantigens, such as those produced by Staphylococcus aureus, induce toxic shock syndrome?

<p>massive T cell activation and cytokine release</p> Signup and view all the answers

Panton-Valentine leukocidin, produced by CA-MRSA, targets and destroys ______.

<p>leukocytes</p> Signup and view all the answers

Match the following Staphylococcus aureus exotoxins with their primary effects:

<p>Protein A = Binds to the Fc portion of IgG, preventing opsonization Coagulase = Promotes fibrin formation around bacteria, protecting it from phagocytosis Hemolysins = Destroys red blood cells, neutrophils, macrophages, and platelets Leukocidins = Destroys leukocytes (white blood cells)</p> Signup and view all the answers

How does Staphylococcus epidermidis typically cause infections in compromised hospital patients?

<p>By migrating from the skin along medical tubing like Foley catheters or intravenous lines. (D)</p> Signup and view all the answers

Staphylococcus epidermidis is inherently pathogenic and always causes disease when present on the skin.

<p>False (B)</p> Signup and view all the answers

After isolating a gram-positive coccus in clusters from a culture, what specific test does a microbiology laboratory typically perform to differentiate Staphylococcus aureus from other staphylococci?

<p>coagulase test</p> Signup and view all the answers

Frequent contamination of blood cultures by Staphylococcus epidermidis occurs when the needle passes through skin covered with Staphylococcus epidermidis, highlighting its role as a common skin ______.

<p>contaminant</p> Signup and view all the answers

Which of the following tests is least likely to be used in the initial identification of Staphylococcus aureus from a clinical sample?

<p>Antibiogram to determine antibiotic susceptibilities. (D)</p> Signup and view all the answers

Which characteristic of Staphylococcus epidermidis contributes most significantly to its ability to colonize prosthetic materials in bacteremia cases?

<p>Presence of a polysaccharide capsule facilitating adherence. (B)</p> Signup and view all the answers

A single positive culture is generally sufficient to confirm Staphylococcus epidermidis bacteremia.

<p>False (B)</p> Signup and view all the answers

Which of the following is a key virulence factor of Staphylococcus aureus responsible for scalded skin syndrome?

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

Staphylococcus aureus possesses a __________ surrounding its peptidoglycan cell wall, enhancing its defense mechanisms.

<p>microcapsule</p> Signup and view all the answers

What is the primary effect of Staphylococcus aureus enterotoxins on the human body?

<p>Gastrointestinal distress characterized by vomiting and diarrhea. (B)</p> Signup and view all the answers

Toxic Shock Syndrome Toxin-1 (TSST-1) is unique to Staphylococcus aureus and has no analogous toxins produced by other bacteria.

<p>False (B)</p> Signup and view all the answers

What is the significance of penicillin-binding proteins (PBPs) in Staphylococcus aureus?

<p>PBPs are essential for cell wall synthesis, and changes in PBPs can lead to antibiotic resistance.</p> Signup and view all the answers

How does the microcapsule of Staphylococcus aureus contribute to its pathogenicity?

<p>By enhancing adherence to host tissues and evading phagocytosis. (D)</p> Signup and view all the answers

Staphylococcus aureus produces __________ exotoxins, which are responsible for causing food poisoning symptoms.

<p>enterotoxins</p> Signup and view all the answers

Match the Staphylococcus aureus exotoxin with its primary effect:

<p>Exfoliatin = Causes scalded skin syndrome Enterotoxins = Induces vomiting and diarrhea TSST-1 = Leads to toxic shock syndrome</p> Signup and view all the answers

Flashcards

Blood draws from 2 sites

Drawing blood from two different sites helps to differentiate between a true bloodstream infection and contamination when Staphylococcus epidermidis is present.

Coagulase-positive, Gram-positive cocci

If a lab reports coagulase-positive, Gram-positive cocci in clusters, the bacteria is Staphylococcus aureus.

Coagulase function

This enzyme activates prothrombin, causing blood to clot.

Coagulase-negative staph

Staphylococcus epidermidis and Staphylococcus saprophyticus are two species that are coagulase-negative.

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Single sample S. epidermidis

A skin contaminant is suspected if only one blood sample grows Staphylococcus epidermidis.

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S. epidermidis Adherence

Polysaccharide capsule allows Staphylococcus epidermidis to stick to prosthetic materials.

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Staphylococcus aureus Exfoliatin

A diffusible exotoxin that causes scalded skin syndrome.

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Staphylococcus aureus Enterotoxins

Exotoxins that cause food poisoning, leading to vomiting and diarrhea; they are heat stable.

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Staphylococcus aureus TSST-1

An exotoxin analogous to streptococcal pyrogenic toxin but much more deadly; causes toxic shock syndrome.

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Staphylococcus epidermidis bacteremia

If 2 cultures are positive, the likelihood of bacteremia with Staphylococcus epidermidis is high.

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Protein A

Binds to the Fc portion of IgG, protecting the organism from opsonization and phagocytosis.

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Coagulase

An enzyme that promotes fibrin formation around bacteria, shielding it from phagocytosis.

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Hemolysins

Exotoxins that destroy red blood cells, neutrophils, macrophages, and platelets.

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Leukocidins

Exotoxins that destroy leukocytes (white blood cells).

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Superantigens

Binds to MHC class II molecules on antigen-presenting cells, causing a massive T cell response and cytokine release, leading to toxic shock syndrome.

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Gram stain

A staining technique used to differentiate bacteria based on their cell wall structure.

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Catalase test

A test that detects the presence of the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen.

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Culture (microbiology)

A method of propagating microorganisms in a controlled environment to identify the specific organism causing an infection.

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Staphylococcus epidermidis

A Gram-positive coccus that commonly lives on the skin without causing disease.

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Coagulase test (Staphylococcus)

A test used to differentiate Staphylococcus aureus from other coagulase-negative Staphylococci.

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Staphylococcus aureus defenses

A microcapsule and thick peptidoglycan cell wall protect this critter.

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Exfoliatin definition

An exotoxin that causes the skin to slough off.

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Enterotoxins definition

These exotoxins cause vomiting and diarrhea in food poisoning.

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TSST-1 definition

Superantigen, more deadly than streptococcal pyrogenic toxin.

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Polysaccharide capsule

Allows S. epidermidis to stick to prosthetic materials.

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Penicillin binding protein

A component of S. aureus that surrounds the cell membrane

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Exotoxins

Can be excreted from the cytoplasm to wreak havoc

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Staphylococcus aureus weapons

Protein weapons used as defense and offense

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Exfoliatin

Exotoxin that causes the skin to peel off

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Enterotoxins

Released by S. aureus and cause vomiting and diarrhea

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Study Notes

  • S. aureus: tissue barrier disruption, hemolysis and leukocyte lysis, as well as tissue proteins degradation.
  • S. aureus disrupts the tissue by using hemolysins like α-toxin and β-toxin.
  • Hemolysis is perforating red blood cells.
  • S. aureus also uses leukocyte lysis and pyroptosis to disrupt tissue.
  • S. aureus degrades host proteins by using SspA, Staphopain, Spl, Aur and PSMs.
  • Nucleic acid degradation involves the use of Nuc enzyme.
  • Lipid degradation involves the use of Lipases.
  • Cytokine production is amplified by SAg's.
  • T cell and B cell expansion
  • Activation of host zymogens
  • Preventing infection require coating used to prevent initial formation and attachment of pathogenic bacteria to 1 the surface of implantable devices such as catheters.
  • Bacteria attach to catheter and forms a biofilm that can protect the cells against antibiotics and antiseptics that would remove them by force
  • Coating is a hydrophilic surface. Water molecules tightly bind to the catheter surface
  • Bacterial cells expend more energy to adhere to the surface as water molecules are already bound.
  • Biofilm formation and risk of infection both decrease.
  • In an outpatient setting, Clindamycin is often a good choice as an antibiotic
  • The CA-MRSA strands is a new strand of MRSA that is easily transferable among staph bacteria,
  • CA-MRSA is now the predominant methicillin resistant staphylococcus bacterium acquired both in and outside the hospital. It also carries few resistant mutations
  • SCCmec is spread via transferrable elements and the SCCmec element is smaller in CA-MRSA

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Description

Explore Staphylococcus aureus identification, key enzymes like prothrombin activators, and differentiation from similar species. Learn about its unique exotoxins, including the one causing scalded skin syndrome, cell wall structure, and adherence mechanisms of Staphylococcus epidermidis. Test your understanding of Staphylococcus species and their characteristics.

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