Effect of fresh guinea-pig serum on the toxicity of Bordetella pertussis and Bordetella parapertussis

Abstract

The effect of fresh guinea-pig serum on the toxicity of Bordetella pertussis and B. parapertussis has been investigated. Cultures were grown on Bordet-Gengou medium, mixed with fresh guinea-pig serum and injected into mice by the intraperitoneal route. Much lower LDse values were found when the animals were injected with mixtures of B. pertussis and guinea-pig serum. The cultures of 12 B. pertussis strains showed LDses between 1·10 and 3·25 billion bacteria after the addition of fresh guinea-pig serum. The LDse values of the control cultures ranged between 2·68 and 8·06 billion bacteria. Compared with the controls the LDses of the cultures mixed with fresh guinea-pig serum were significantly lower (P<0·05). Increased mortality was observed when cultures of B. pertussis of low toxicity were mixed with fresh guinea-pig serum and injected into mice. Such cultures after the addition of serum caused approximately 100% mortality in the injected animals. The effect of fresh guinea-pig serum on the toxicity of B. parapertussis cultures was assayed. Cultures highly toxic for mice were less toxic after the addition of fresh guinea-pig serum. The cultures of toxic strains which caused 50% mortality failed to kill mice after addition of fresh guinea-pig serum. Cultures of B. pertussis and B. parapertussis strains tested for toxicity showed variable susceptibility to the bactericidal action of guinea-pig serum. In cultures of both Bordetella species between 60 and 99% of the bacteria were killed by serum. No correlation between toxicity and the bactericidal activity of fresh guinea-pig serum toward B. pertussis and B. parapertussis strains was observed.