Genetic and biochemical characterization of Brucella abortus strain RB51

Brucella abortus strain RB51, a naturally derived rough variant, has been proposed to replace strain 19 for use as a vaccine against brucellosis in cattle. Utilizing fingerprinting and standard biotyping techniques, it was possible to differentiate RB51 from other brucellae and to ascertain the stability of RB51. Standardization of a genomic fingerprinting procedure using restriction endonuclease profiles of total DNA from Brucella are described. Although the focus was principally on B. abortus isolates from cattle, the investigation included field isolates from bison and elk, reference strains, vaccinal strains, and genetically-engineered brucellae;Pulsed-field gel electrophoresis profiles of the reference type strains allowed separation of the strains to the level of species. A unique fingerprint relative to other brucellae was discovered for RB51, using profiles of genomic DNA digested with the restriction endonuclease Xba I;Stability of RB51 after animal passage and high passage on artificial media was determined using standard methods for characterizing brucellae. Techniques included biochemical, morphological, antigenic, phage susceptibility, and antibiotic resistance. RB51 retained rough colonial morphology with no detectable O-antigen of Brucella lipopolysaccharide and remained resistant to rifampin or to penicillin and sensitive to tetracycline following repeated passage. No detectable changes in characteristic oxidative metabolic profiles on selected amino-acid or carbohydrate substrates were demonstrated following in vivo or repeated in vitro passage;Genomic fingerprints of reference strains and biovars of Brucella were analyzed to obtain information on the genetic relatedness among the strains. Included were four newly described isolates of Brucella from the common seal, harbor porpoise, and common dolphins. Distance matrix analyses were done and a dendrogram was constructed. Results support the designation of an additional genomic group(s) of Brucella;Comparison of cell wall structure of RB51 and B. abortus strain 2308 using transmission electron microscopy revealed variation in surface properties indicating modifications in acidic polysaccharide associated with lipopolysaccharide. The ultrastructural characteristics of the cell wall contributes to the understanding of B. abortus by demonstrating surface components that may be involved in cellular interactions