The immunization of guinea-pigs and mice with a whole-culture extract of a smooth and a rough strain of Brucella abortus.

A purified killed vaccine developed for use in man from the smooth strain 544 and previously tested in mice (Keppie, Witt and Smith, 1971) has now been shown to immunize guinea-pigs without the addition of adjuvant. A similar vaccine prepared from the rough strain 45/20 also immunized guinea-pigs but to a slightly lesser degree. The activity of both vaccines in the guinea-pig was markedly enhanced by the use of water-in-oil emulsions. A commercially available killed vaccine, “Duphavac”, prepared from strain 45/20 for use in cattle, was slightly more active in guinea-pigs than the emulsified whole-culture extract of “544” possibly because its oily adjuvant was different. In mice, all the “45/20” vaccines were only feebly protective even when given with oily adjuvant, in sharp contrast to the “544” vaccines which were highly active in this animal, with or without adjuvant. As expected, the “45/20” vaccines were much less agglutinogenic than the “544” vaccines but both produced a similar degree of delayed hypersensitivity in guinea-pigs. It is suggested that the whole-extract vaccine from strain 544 is suitable for a trial in man.