29. Staph Aureus Slide Agglutination

Question 1

What is the percentage/ratio of people who have S.Aureus on their skin or nasal passages at any given point in time?

Answer 1

25%

1/4

Question 2

What anatomical sites are commonly infected by S. Aureus?

Answer 2

• Skin (impetigo)
• Hair follicles (boils)
• subcutaneous connective tissue (cellulitis)
• heart (endocarditis)
• bone (osteomyelitis)
• lungs (pneumonia)

Question 3

How can S. Aureus cause septic shock?

Answer 3

-Migrates from local infection into the blood, which results in the systemic inflammatory response syndrome (septic shock)

Question 4

What are the two proteins in the outermost layers of the cell walls of S. Aureus?

Answer 4

• clumping factor A (ClfA)

- protein A (SpA)

Question 5

What is the function of the protein clumping factor A (ClfA)?

Answer 5

-allows S. Aureus cells to bind to human fibrinogen

Question 6

Where is fibrinogen normally found? Function?

Answer 6

• soluble plasma protein
  
  • during normal blood clotting, thrombin activates fibrinogen
• Once activated fibrinogen > fibrin
  
  • fibrin proteins attach to each other, forming long fibbers that tangle and form a mesh
  • fibrin net traps blood cells, forming a blood clot

Question 7

What is the function of protein A (SpA)?

Answer 7

-allows S. Aureus to defeat antibodies

Question 8

Structure of an antibody

Answer 8

• Y shape
  
  • 2 binding sites
  • constant region

Question 9

Are the ClfA and SpA proteins of S. Aureus virulence factors?

Answer 9

Yes

ClfA

- binds to fibrinogen proteins in plasma to allow hundreds of S. Aureus cells to clump together 
- helps attach to human tissues and to implanted medical devices

SpA

- binds to Fc region (constant) of most blood antibodies
- prevents stimulation of WBC or activation of complement proteins

Question 10

Define agglutination

Answer 10

• clumping of particles

- process the occurs when an antigen is mixed with its corresponding antibody

Question 11

How to test if a bacterium has the enzyme catalase

Answer 11

• add hydrogen peroxide to culture plate
  
  • if there is vigorous bubbling= contains catalase
  • no bubbling = no catalase
• gram stain
  
  • if gram - = no catalase
  • if gram + = contains catalase

Question 12

How does S. Aureus appear during a clinical test?

Answer 12

• Gram stain: Gram positive cocci
• catalase test : +
• StaphTex blue : +