Staphylococcus aureus: Virulence and Toxin

Q. 1

All of the following statements about staphylococcus aureus are true, EXCEPT:

A		Most common source of infection is cross infection from infected people
B		About 30% of general population are healthy nasal carriers
C		Epidermolysin and TSS toxin are superantigens
D		Methicillin Resistance is chromosome mediated.

Q. 1

All of the following statements about staphylococcus aureus are true, EXCEPT:

A		Most common source of infection is cross infection from infected people
B		About 30% of general population are healthy nasal carriers
C		Epidermolysin and TSS toxin are superantigens
D		Methicillin Resistance is chromosome mediated.

Ans. A

Explanation:

Carriers of staphylococcus aureus are the primary source for cross infection to individuals who do not normally have this bacterium in their commensal microflora.

Individuals normally free from s.aureus may have less immunity against the lethal consequence of S.aureus infection compared with those who are persistent carrier of the species and suffer from endogenous infection.

Most individuals who develop staphylococcus aureus infections are infected with their own colonizing strains.

However, S. aureus may also be acquired from other people or from environmental exposures.

Ref: Jawetz, Melnick and Adelberg’s Medical Microbiology, 23rd Edition, Pages 224 – 228; Staphylococci in Human Disease By Kent B. Crossley, Page 265; Microbiology and Immunology By Monica Gandhi, Page 4; Harrison’s Principles of Internal Medicine, 17th edition, Pages 873 – 879.

Q. 2

An enzyme produced by Staphylococcus aureus that dissolves fibrin clots is:

A		Hyaluronidase
B		Catalase
C		Staphylokinase
D		Lipase

Q. 2

An enzyme produced by Staphylococcus aureus that dissolves fibrin clots is:

A		Hyaluronidase
B		Catalase
C		Staphylokinase
D		Lipase

Ans. C

Explanation:

Pathogenic bacteria release exoenzymes that increase their ability to invade body tissue. These include coagulase, kinases, lipase, hyaluronidase, and collagenase.

All Staphylococci produce catalase, an enzyme responsible for conversion of toxic hydrogen peroxide to water and oxygen which accumulates during bacterial metabolism or is released following phagocytosis.

Kinases dissolve fibrin clots thus enabling the organism to invade and spread throughout the body. Staphylococcus aureus produces staphylokinase which is fibrinolytic.

Coagulase is the exoenzyme produced by Staphylococcus aureus and it clots the plasma.

Lipase hydrolyzes lipids, and aids in the survival of staphylococci in the sebaceous glands.

Hyaluronidase enables pathogen to spread through connective tissue by breaking down hyaluronic acid, the “cement” that holds tissue cells together.

Ref: Francis C.W., Crowther M. (2010). Chapter 23. Principles of Antithrombotic Therapy. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.

Q. 3

Toxin of staphylococcus –

A		Hemolysin
B		Leucocidin
C		Enterotoxin
D		All

Q. 3

Toxin of staphylococcus –

A		Hemolysin
B		Leucocidin
C		Enterotoxin
D		All

Ans. D

Explanation:

Ans. is ‘d’ i.e., All

Q. 4

Staphylococcus aureus remains in the skin for longer period because of –

A		Catalase
B		Coagulase
C		Hyaluronidase
D		None

Q. 4

Staphylococcus aureus remains in the skin for longer period because of –

A		Catalase
B		Coagulase
C		Hyaluronidase
D		None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Hyaluronidase

Hyaluronidase breaks down the connective tissue and helps in the spread of infection.

Q. 5

Toxic shock syndrome is Staphylococcus infection is due to –

A		Superantigen
B		Alpha-hemolysis
C		Coagulase
D		Penton Valentine factor

Q. 5

Toxic shock syndrome is Staphylococcus infection is due to –

A		Superantigen
B		Alpha-hemolysis
C		Coagulase
D		Penton Valentine factor

Ans. A

Explanation:

Ans. is ‘a’ i.e., Superantigen

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Staphylococcus aureus: Virulence and Toxin