LANCEFIELD GROUP-C STREPTOCOCCUS-MILLERI GROUP STRAINS AGGREGATE HUMAN PLATELETS

Lancefield group C Streptococcus milleri group (SMG) strains are the o nly SMG types that are able to aggregate human platelets. Complete agg regation occurred within 10 min of mixing bacterial cells and platelet s together in the ratio 8:1. Substances which (i) chelated cations; (i i) inhibited the cycloxygenase pathway in platelets; (iii) reduced the availability of ADP and disrupted platelet membrane stability; (iv) r educed bacterial aggregation of platelets. The platelet-interacting su bstance on the surface of the SMG appeared to be proteinacious as dige stion of bacterial cells with protease inhibited aggregation whereas t reatment with lipase, periodate or antisera to Lancefield group C poly saccharide had no effect.