A kinetic study of the bacteriolytic and bactericidal action of human serum.

The killing and lysis of Escherichia coli by human serum have been measured simultaneously at frequent intervals for periods of 30–60 minutes. The kinetic effects of varying the amounts of lysozyme, antibacterial antibody and complement have been studied. The rate of lysis is largely controlled by the lysozyme concentration but complement is also necessary. Killing is closely related to complement concentration. Antibody is needed in such small amounts that it is rarely a limiting factor. Inhibition of serum lysozyme by anti-human lysozyme prevents lysis and reduces killing but both are restored to normal by addition of egg-white lysozyme. Both lysis and killing are stopped by bentonite absorption of serum and complete return to normal is not attained by subsequent addition of egg-white lysozyme. In a lysozyme-free system lysis does occur after some delay probably due to the action of complement and antibody alone. In the presence of adequate complement and antibody the loss of complement (measured haemolytically) in bentonite treated serum is inadequate to account for the fall in bactericidal activity. A new bentonite absorbable factor (BAF) essential for complete serum bactericidal power is postulated.