Gram Positive Cocci
Streptococcus all are true except (AIIMS 2011)
|A||Streptodornase cleaves DNA|
|B||Streptolysin O is active in reduced state|
|C||Streptokinase is produced from serotype A, C, K|
|D||Pyrogenic toxin A is plasmid mediated|
Pyrogenic toxin A is plasmid mediated
a. Group A (S.pyogenes) are responsible for almost 90% of human infections due to streptococci. S.pyogenes forms several exotoxins and enzymes which contribute to its virulence, along with the M protein, C polysaccharide, hyaluronic acid capsule and teichoic acids.
b. Hemolysin O and S:Streptolysin O is oxygen labile which is inactive in the oxidised state not in reduced state. Streptolysin S is an oxygen stable hemolysin and so responsible for hemolysis seen around surface colonies of S.pyogenes. Hemolysin O and S are produced by streptococcal groups C and G also.
c. Pyrogenic toxin is also called Erythrogenic or Dick or scarlatiniform toxin. Primary effect of this toxin is induction of fever. Streptococcal pyrogenic toxins ( SPE) A,B and C are superantigens which have the ability to stimulate large no. of T cells by nonspecific binding to the Vβ region of T cell receptor, inducing massive release of inflammatory cytokines. Types A and C are bacteriophage coded and type B gene is chromosomal.
d. Deoxyribonucleases produced by Streptococcus are called streptodornase. This enzyme depolymerises DNA and helps to liquefy the thick pus of pyogenic exudates
e. Streptokinase or fibrinolysin promotes the lysis of human fibrin clots by activation of plasminogen. It is believed to play a role in spread of streptococcal infections by breaking down fibrin barrier around the lesions. It is also produced by streptococcal groups C and K. S.equisimilis is the source of streptokinase used for thrombolytic therapy in patients.