Tag: Staphylococcus aureus: Virulence and Toxin

Staphylococcus aureus: Virulence and Toxin

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 

Quiz In Between


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 

Quiz In Between



Staphylococcus aureus: Virulence and Toxin

Staphylococcus aureus: Virulence and Toxin


VIRULENCE FACTOR:

  • Cell wall associated structures
Techoic acid
  • Adhesion
  • Protection against complement mediated opsonization.
  • Antitechoic acid antibodies found in the patients with active endocarditisndue to S. aureus’
Peptidoglycan

 

  • Inhibits inflammatory response
  • Activates complement system
  • Induce release of cytokines
  • Endotoxin like activity

 

Capsule
  • Adhere to host cell
  • Resist phagocytosis

 

Clumping factor (bound coagulase)

 

  • Cause organism to clump in presence of plasma

 

ProteinA

 

  • Binds to Fc moiety of IgG, exerting antiopsomin
  • Strongly antiphagocytic effect
  • Responsible for Coagglutination

 

Extracellular Enzymes

Free Coagulase
  • Clots plasma by acting along with CRF present in plasma, binding to prothrombin and converting fibrinogen to fibrin
  • Detected by tube coagulase test
  •  8 types. 
  • Most human strain form – A coagulase
staphylokinaseDNAase

 

  • Degrades fibrin clots

 

Hyaluronidase serokinase
  • Hydrolyze the acidic mucopolyysaccharides  present in matrix of connective tissues

 

Nuclease

 

  • heat stable nuclease (DNAse)
Lipases
  • Helps in infecting skin and subcutaneous tissue
Protease
  • Helps spread infection

TOXINS Cytolytic Toxins

α-Hemolysin
  • Protein inactive at 70oC
  • Reactivated paradoxically at 100″C.
  • Less active against human erythrocytes.
  • Leukocidal
  • Cytotoxic
  • Dermonecrotic
  • Neutotoxic
  • Lethal.
β- Hemolysin
  • Hot cold phenomenon
  • Sphingomyelinase
  • Hemolytic for sheep cells. 
δ  – Hemolysin
  • Detergent like effect on cell membranes,
  • Plays role in S. aureus diarrhea
  • disease
γ – Hemolysin 
  • Bicomponent protein. 
Leukocidin (Panton valentine Toxin
  • Bi component toxin
  • Associated with farunculosis
  • Important virulence factor in MRSA infection.
  • Kills WBCS by producing holes in their CM

Enterotoxin

  • Act on ANS to cause illness
  • Preformed
  • Types:A, B, C 1-3, D, E and H
  • Heat stable toxin
  • Responsible for staphylococcal food poisoning which occur 2-5 hrs after consuming meat and fish or milk products.

Source:

  • Usually food handler which is carrier.
  • Mechnism: Type A toxin is responsible for most cases.
    • Toxin acts directly on autonomic nervous system (Vagal stimulation) andvomiting center.

TSST

  • Produce fever, skin rashes,diarrhoea,conjunctivitis,and death to shock
  • TSST-1 = Enterotoxin F = Pyrogenic Exotoxin C is responsible for most cases.
  • TSST-1 binds to MHC class II molecules, yieldingT-Cell stimulation.
  • Staph. Enterotoxin and TSST are super antigen 
  • Leading to an excessive and non regulated immune response.

Exfoliating toxin/Epidermotolytic Toxin / ET / Exfoliatin

  • Breaks intracellular bridges in the stratum granulosum of epidermis
  • Causes its separation from underlying tissue
  • Resulting in a blistering and exfoliating disease of skin
  • Cause staphylococcal scalded skin syndrome (SSS).
  • Severe form is called Rittels disease in neonate arrd toxic epidermal neuolysis in elderly.
  • Milder form are pemphigus neonatorum and bullous impetigo.

Two type:

  • ETA (chromosomal gene product, heat stable)
  • ETB (plasmidnmediated, heat labile). 
  • Possess serine protease activity which triggers exfoliation.

Exam Important

  • About 30% of general population are healthy nasal carriers
  • Epidermolysis and TSS toxin are superantigens
  • Toxic shock syndrome is Staphylococcus infection is due to superantigen, Leucocidin and Hemolysin
  • Staphylokinase enzyme produced by Staphylococcus aureus that dissolves fibrin clots 
  • Toxins of Staphylococcus are Enterotoxin 
  • Staphylococcus aureus remains in the skin for longer period because of Hyaluronidase 
  • Methicillin resistance is chromosome mediated

 

Don’t Forget to Solve all the previous Year Question asked on Staphylococcus aureus: Virulence and Toxin

Module Below Start Quiz

Free Mini Course on Stomach

Mini Course – Stomach

22 High Yield Topics in Stomach

in Just 2 Hours

Submission received, thank you!

Close Window
Malcare WordPress Security