Identification of Brucella abortus B19 vaccine strain by the detection of DNA polymorphism at the ery locus.

As sensitivity to erythritol is the main feature of the Brucella abortus B19 vaccine strain, an attempt to define the genetic basis of this phenotypic trait was made in order to explore its usefulness as a means of molecular identification of strain B19. With this purpose, an erythritol-sensitive derivative of B. abortus strain 2308 was generated by Tn5 transposition methods. Restriction fragments from a cloned 13 kb Tn5-containing EcoRI fragment from the ery locus of strain 2308 were used to probe DNA from B. abortus B19 and other Brucella reference strains. Genetic rearrangement in strain B19 was revealed by the display of restriction fragment length polymorphisms at the ery locus. No pattern differences were detected among all other Brucella strains tested. The polymorphism exhibited by B19 represents the first characterization of this vaccine strain at a molecular level, and can be used to distinguish it from all other Brucella species.