IMMUNIZATION AGAINST BRUCELLA INFECTION' II. EFFECTVENES OF A STREPTOMYCIN-DEPENDENT STRAN OF

In previous reports (Elberg and Herzberg, 1953; Herzberg and Elberg, 1953) the isolation and characteristics of a streptomycin-dependent mutant of Brucella melitenis were described.2 The streptomycin-dependent strain retained the biochemical and antigenic characteristics of the virulent parent strain but differed in a require-ment for streptomycin for its growth. Growth in vivo was not influenced detectably by in vivo administration of streptomycin. The following studies describe the capabilities of this strain for inducing protection of mice and guinea pigs against experimental infection with virulent B. melitensis. MATERIALS AND METHODS These were described in considerable detail in the first paper of the series (Herzberg and Elberg, 1953) and need not be restated here. Suffice it to say at this point that protection was asessed in terms of the ability of the animal to sterilize spleen tissue of the organisms constituting the "challenge". EXPERIMENTAL RESULTS The first sets of observations deal with. mice which had received one injection of streptomycin-dependent strain of B. meliten8is. Mice were inoculated subcutaneously with doses ranging from 106 to 108 organisms, both large and small colony forms being employed. After a rest period of 5 weeks, the immunities were tested against graded challenge doses. Thre