The characteristics of a variant strain of Brucella melitensis\ud Rev l

Circumstantial evidence is presented for the occurrence of a variant of a vaccine strain of B. melitensis Rev\ud 1, designated "FSA"(foreign South African). FSA resembles Rev 1 in its reactions to penicillin and streptomycin\ud but reacts closer to a field strain of B. melitensis as regards dye (thionine and basic fuchsin) sensitivity and\ud colony size.\ud \ud Although colonies of Rev 1 were consistently smaller than other B. melitensis strains, their size was 0,75 mm as opposed to the 1-2 mm reported in the literature, while B. melitensis 16M colonies were 1,25-1,5 mm as opposed to the 3-4 mm previously reported. \ud \ud Rev 1 was found to be urease positive, unless a test of low sensitivity was applied