Mechanism of Action of Specific Antiserum on Pasteurella septica

Circumstantial evidence suggests that the ability of the host to prevent the uptake of iron by pathogenic bacteria may constitute an important means of defence. A detailed biochemical study of the way antisera exert their antibacterial effects and the possible involvement of iron has now been initiated. Work with Pasteurella septica antiserum has revealed a totally unsuspected way in which antiserum and complement exert their antibacterial effects. The process is very quick and specific and results in the cessation of bacterial multiplication; cells in stasis then appear to be killed by the operation of a secondary event. The inhibitory process operates by affecting the biochemistry of the bacterial cell leading first to an inhibition of net RNA synthesis and then to an inhibition of all macromolecular synthesis. The presence of free iron in the serum did not prevent the initiation of the inhibition but it did allow macromolecular synthesis, cell multiplication and rapid growth to be resumed later. In contrast, the presence of haematin in the serum allowed the cells to continue multiplying in the presence of antiserum without delay. Addition of haematin to bacteria which had been inhibited by antiserum restored net RNA synthesis immediately. Net protein synthesis and multiplication were restarted within 15–20 min and DNA synthesis in 40 min.