The antibacterial effect of Bordetella pertussis antisera.

Antisera to are bactericidal for some strains of in the presence of complement and lysozyme. Phase I bacilli, virulent for mice by the intracerebral and intranasal routes, are sensitive to the bactericidal effect; most mouse avirulent strains are not. Most of the bactericidal antisera belong to one of two types according to the concentration of antibody and complement that are optimally lethal. Type 1 antisera are bactericidal in the range 1/30 to 1/900 with guinea-pig serum as the complement source at 1/18 to 1/100. Type 2 antisera are characterized by a zone without bactericidal activity over similar antiserum and complement dilutions. Their bactericidal activity is made evident by diluting the antiserum further, by increasing the amount of complement, or by adding tissue homogenates, body fluids or crystalline lysozyme. The two types are further characterized by the differing requirements of the bactericidal system for the individual components of haemolytic complement. The combined lethal action of antibody, complement and lysozyme is rapid. In the early stages it is partly inhibited by substances in the medium used for estimating viable counts indicating that in its initial stages the reaction is bacteriostatic rather than bactericidal.