Brucellosis is a costly disease of water buffaloes (Bubalus bubalis). Latent infections and prolonged incubation of the pathogen limit the efficacy of programs based on the eradication of infected animals. We exploited genetic selection for disease resistance as an approach to the control of water buffalo brucellosis. We tested 231 water buffalo cows for the presence of anti-Brucella abortus antibodies (by the agglutination and complement fixation tests) and the Nramp1 genotype (by PCR-denaturing gradient gel electrophoresis). When the 231 animals (58 cases and 173 controls) were divided into infected (seropositive) and noninfected (seronegative) groups and the Nramp1 genotypes were compared, the seropositive subjects were 52 out of 167 (31%) in the Nramp1A ؉ (Nramp1AA or Nramp1AB) group and 6 out of 64 (9.4%) in the Nramp1A ؊ (Nramp1BB) group (odds ratio, 4.37; 95% confidence limits, 1.87 to 10.19; 2 , 11.65 for 1 degree of freedom). Monocytes from Nramp1BB subjects displayed significantly (P < 0.01) higher levels of Nramp1 mRNA than Nramp1AA subjects and also a significantly (P < 0.01) higher ability in controlling the intracellular replication of several Brucella species in vitro. Thus, selection for the Nramp1BB genotype can become a valuable tool for the control of water buffalo brucellosis in the areas where the disease is endemic.

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A bacteriophage lytic for Escherichia coli O157:H7 was isolated from bovine manure. Following in-vivo selection, the phage acquired the capacity to persist in the circulatory system of mice for at least 38 days. When mice were infected experimentally with E. coli O157:H7 (10(7) CFU/mouse), simultaneous injection of the mice with phage (10(8) PFU/mouse) cleared E. coli O157:H7 from the mice within 48 h.

We tested 413 water buffalo cows (142 cases and 271 controls) for the presence of anti-Brucella abortus antibodies (by the skin test, the agglutination test, and the complement fixation test) and the Nramp1 genotype (by capillary electrophoresis). Four alleles (Nramp1A, -B, -C, and -D) were detected in the 3 untranslated region of the Nramp1 gene. The BB genotype was represented among only controls, providing evidence that this genotype confers resistance to Brucella abortus. The monocytes from the BB (resistant) subjects displayed a higher basal level of Nramp1 mRNA and a lower number of viable intracellular bacteria than did the monocytes from AA (susceptible) subjects. The higher basal level of the antibacterial protein Nramp1 most probably provides the BB animals with the possibility of controlling bacteria immediately after their entry inside the cell.