Release of 14C label and complement killing of Escherichia coli.

When Escherichia coli labelled with 14C were killed by complement, characteristic 14C compounds were released even when complete cell disintegration was prevented or delayed by removal of lysozyme. Treatment with heated serum only resulted in the loss of small molecular weight compounds. Separation of the products was made easier if whole serum was replaced by a salt-precipitated fraction which contained no albumin or lysozyme but retained antibody and complement. Fractionation of the bacterial products on Sephadex G-200 showed two radioactive peaks containing lipids and proteins of which a preliminary examination was made. The release of these compounds was related to complement action, since they were not found when bacteria were killed by streptomycin or ultra-violet light in the absence of complement. Nor were they found when resistant bacteria were treated with complement and survived. The possible modes of action of complement on bacterial cell walls are discussed.