In vitro cytotoxic effect of alpha-hemolytic and nonhemolytic Escherichia coli on human blood granulocytes and monocytes.

The in vitro cytotoxic effect of Escherichia coli on human phagocytic blood cells in the presence of fresh autologous plasma was assessed using (i) a technique by which cell damage was quantified by measuring the release of chromium 51 from labelled granulocytes and (ii) a technique based on the degree of morphological cell damage induced in monocytes. All of 109 alpha-hemolytic strains were cytotoxic, the cytotoxic effect ranging from very weak to strong. Log-phase cultures had the strongest cytotoxic effect, the individual microorganisms being most cytotoxic in the early log-phase. Plateau-phase cultures progressively lost their cytotoxic ability and 24 h old cultures were almost noncytotoxic. Strongly cytotoxic strains induced high degrees of cell injury, caused an abrupt damage during the first 20 min of incubation and were able to induce injury with few bacteria present. Weakly cytotoxic strains induced only low degrees of cell injury, caused a more gradually developing damage, and were able to induce injury with only high numbers of bacteria present. All of 75 nonhemolytic and 3 beta-hemolytic strains were noncytotoxic.