HAEMOLYSINS AS BACTERIAL TOXINS

INTRODUCTION:  S. pyogenes elaborates two haemolysins. One of these is oxygen labile and hence named as streptolysin O (SLO) and the other being stable to the action of oxygen and soluble in serum is designated as streptolysin S (SLS). 

Streptolysin O (SLO).  It is responsible for haemolysis in the deeper layers of blood agar where streptococci grow in the absence of oxygen. SLO is toxic for red blood cells, white blood cells, as well as myocardial cells in tissue cultures.   

Streptolysin S (SLS).  This agent is responsible for the haemolytic zone around the streptococcal colonies growing on the surface of blood agar in the presence of oxygen.  It is a soluble product which cannot withstand boiling for more than 60 minutes.  Streptococcal pyrogenic exotoxins exert profound effect on immune system, including enhancement of susceptibility to endotoxic shock, blockade of reticuloendothelial system and alterations in the T cell function.  These toxins are produced only by those strains of group A streptococci which are carrying temperate phage in their genome.  Classically it was thought that this toxin caused red reaction in the skin of nonimmune individual (positive Dick test) and no reaction in individuals with immunity (negative Dick test).  Antitoxin injected into the skin of a patient with scarlet fever causes localised blanching due to neutralization of erythrogenic toxin (Schultz-Charlton reaction).  

Streptokinase:  This is a fibrinolysin which is produced by the group A streptococci.  Strains from groups C and G also produce it.  It transforms the plasminogen of human plasma into plasmin, an active proteolytic enzyme that digests fibrin and other proteins.

RELATED;

1.  STREPTOCOCCUS  2.  VIRULENCE FACTORS OF MICROBES

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