Bactericidal action of fresh rabbit blood against Brucella abortus.

A photometric method was used to measure the bactericidal kinetics for Brucella abortus of freshly drawn rabbit blood during the time before clotting. This antibrucellar activity varied between rabbits in different immunologic states. Nonimmunized rabbits had moderate bactericidal activity after a lag of about 2 min. The blood of some immunized rabbits gave an immediate and strong kill, but in certain other immunized rabbits, especially when hyperimmunized, the bactericidal activity was inhibited. It appeared that serum bactericidins and complement are sometimes as active in unclotted blood as they are in serum. However, this bactericidal activity can be either increased or neutralized by immunization. The prozone bactericidal inhibition phenomenon (Neisser-Wechsberg) found in immune serum may, in fact, reflect inhibition taking place in vivo. Inhibition of the bactericidal activity in blood can contribute to the persistence of chronic infections and individual variations in resistance.

Neutralization of beta-lysin and cationic bactericidal agents by acidic phospholipid.

Acidic phospholipids neutralized the antistaphylococcal activity of rabbit, human, and rat serum and purified rabbit beta-lysin as well. Several tissue bactericidal factors and cationic antibiotics were also neutralized. The neutralizing ability of all anionic lipids tested, together with the lack of this ability for the electrostatically neutral phosphatidylcholine, suggested that neutralization resulted from formation of electrostatic complexes between negative charges on the lipids and positive charges on the bactericidal substances. The neutralization of these host defense systems by phospholipids can explain the ability of phospholipids to increase bacterial virulence.