Rifampin is one of the most potent and broad-spectrum antibiotics against bacterial pathogens. Its bactericidal activity is due to its ability to bind to the ␤ subunit of the DNA-dependent RNA polymerase encoded by the rpoB gene. Mutations of the rpoB gene have been characterized in rifampin-resistant (Rif r ) strains of Escherichia coli and Mycobacterium tuberculosis. The genetic bases of Rif r in Brucella spp. are still unknown. In the present study, the nucleotide sequences of the rpoB gene of the Rif r vaccine strain Brucella abortus RB51 and of 20 Rif r clones derived in our laboratory from two Brucella melitensis isolates were determined. These sequences were then compared to those of the respective rifampin-susceptible (Rif s ) parental strains and to the published B. melitensis strain 16M. All Rif r strains carried one or more missense mutations mapping in two regions of the rpoB gene. These two "hot" regions were investigated in eight additional Rif r Brucella laboratory mutants and in 20 reference Rif s Brucella strains. rpoB mutations were found in all Rif r mutants. In contrast, no missense mutations were found in any analyzed Rif s strains. Our results represent the first from a study of the molecular characterization of rpoB mutations in resistant Brucella strains and provide an additional proof of the association of specific rpoB mutations with the development of the Rif r phenotype in prokaryotes. In addition, because of the relationship between Rif r and the attenuation of virulence in Brucella spp., studies of virulence in these mutants may provide useful information about the genetic basis of pathogenesis in Brucella.Rifampin is one of the most potent and broad-spectrum antibiotics against bacterial pathogens and is an important component of effective multidrug therapies for the treatment of brucellosis in humans (2,5,26). Previously reported data have indicated that the addition of rifampin to media tends to turn Brucella abortus cultures rough and that organisms with rifampin resistance (Rif r ) are less virulent than rifampin-susceptible (Rif s ) strains (17, 23). Rifampin was therefore utilized to obtain the stable, rough, and attenuated B. abortus strain RB51, currently used in the United States as the official vaccine for brucellosis eradication in cattle. The roughness and attenuation are two important characteristics for the vaccine strain RB51, which is able to induce an adequate, protective cell-mediated response against infection with virulent Brucella strains without interfering with standard serological tests for brucellosis diagnosis (7,15,16,18,19,20,22,27). Strain RB51 was derived by repeated passaging of the smooth and virulent B. abortus strain 2308 on media supplemented with rifampin (23). Its high level of Rif r constitutes a useful biochemical marker for its identification. This characteristic was used to develop a selective medium to assist in the recovery of the vaccine strain RB51 from experimental and field samples for its isolation (10).The genetic bases for Rif r in ...

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Anthrax is a disease of human beings and animals caused by the encapsulated, spore-forming, Bacillus anthracis. The potential role of insects in the spread of B. anthracis to humans and domestic animals during an anthrax outbreak has been confirmed by many studies. Among insect vectors, the house fly Musca domestica is considered a potential agent for disease transmission. In this study, laboratory-bred specimens of Musca domestica were infected by feeding on anthrax-infected rabbit carcass or anthrax contaminated blood, and the presence of anthrax spores in their spots (faeces and vomitus) was microbiologically monitored. It was also evaluated if the anthrax spores were able to germinate and replicate in the gut content of insects. These results confirmed the role of insects in spreading anthrax infection. This role, although not major, given the huge size of fly populations often associated with anthrax epidemics in domestic animals, cannot be neglected from an epidemiological point of view and suggest that fly control should be considered as part of anthrax control programs.

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This study indicated that mice immunized with Brucella abortus RB51 bacteria and subsequently challenged with B. abortus 2308 were protected from reinfection. After vaccination, both Th1 and Th2 cytokine patterns were observed. Of those, the early production of gamma interferon seems to have the prominent role in inducing an immunologically based protection.