STREPTOKINASE ACTIVITY AMONG GROUP-A STREPTOCOCCI IN RELATION TO STREPTOKINASE GENOTYPE, PLASMINOGEN BINDING, AND DISEASE MANIFESTATIONS

Certain genotypic variants of streptokinase (ska) of beta-hemolytic st reptococci group A have been associated with acute post-streptococcal glomerulonephritis (APSGN). In our earlier studies on strains isolated from Ethiopian children with various streptococcal disease manifestat ion, we reported an even distribution of streptokinase genotypes with no association to disease patterns. Considering the possibility that s trains could differ in their ability to secrete the protein, levels of streptokinase activity in culture supernatants of these strains were determined by a plasminogen activation assay using a synthetic tripept ide, H-D-valyl-leucyl-lysin-p-nitroaniline, as a substrate. Of the 53 streptococcal group A strains, ten (19%), which belonged to genotype s ka4 and ska8, did not activate human plasminogen. These strains did no t activate bovine, sheep, horse, rabbit or porcine plasminogens either . They represented at least five M protein and non-typeable serotypes, and were characterized by high human plasminogen binding activity. Si x of the 53 strains (11%) harbouring genotype ska3 and ska7 showed low levels of human plasminogen activation. Strains of ska 1 and ska2, 37 /53, activated human plasminogen at a higher level (p < 0.005). Levels of plasminogen activation were not significantly different among the ska1 and ska2 strains associated with various streptococcal disease ma nifestations. Antibody levels against streptokinase were higher (p < 0 .05) in convalescent sera from acute rheumatic fever and APSGN patient s in comparison with sera from other patient categories and healthy co ntrols. Streptokinase genotype and in vitro streptokinase production d o not correlate directly to streptococcal disease manifestation, indic ating a probable significance of additional streptococcal and/or host factors in the initiation of APSGN.