In vitro cytotoxic effect of alpha-hemolytic Escherichia coli on human blood granulocytes. Correlation with size of alpha-hemolysin production.

The correlation of the in vitro cytotoxic effect of 107 alpha-hemolytic strains of Escherichia coli with various other bacterial characteristics was investigated. Damage to human blood granulocytes in the presence of fresh or heated autologous plasma was quantified by measuring the release of chromium-51 from labelled cells. 95 strains had a cytotoxic effect which was equal in the presence of fresh or heated plasma, whereas 12 strains showed an effect which was reduced in fresh compared with heated plasma. The cytotoxic effect increased as the number of bacteria per granulocyte was increased. The average size of the alpha-hemolysin production of the strains was 185 HU50/ml ranging from 3-2519HU50/ml. The cytotoxic effect of the strains was directly correlated with the size of the alpha-hemolysin production. The cytotoxic effect was not correlated with the O-antigen serotype or the type of infection from which the strains were derived. These results indicate that the ability to produce alpha-hemolysin is the bacterial characteristic which is of decisive importance for the cytotoxicity of alpha-hemolytic E. coli towards human blood granulocytes.