Isolation of Brucella abortus strain RB51 from two buffalo fetuses

are reared, mainly for the milk used to produce mozzarella cheese. The buffalo herds are distributed across 2246 farms (ISTAT 2000), mostly in the Campania region. Brucellosis is endemic in large areas of this region, and Brucella abortus biovars 1 and 6, and Brucella melitensis biovar 3, are the most frequently isolated strains (Galiero 2004). The Regional Health Authority of Campania has set up a special eradication programme for the control of brucel-losis in buffaloes, using a prophylactic vaccination regimen with strain 19 or RB51 vaccines. RB51 is a live, attenuated vaccine derived from the virulent B abortus strain 2308 by serial passage of colonies expressing rough morphology in culture media containing variable concentrations of rifampin (Schurig and others 1991). The RB51 strain cannot be identi-fied by the serological tests used in conventional brucellosi