A Brucella bacterium is modified by partial or complete deletion of the
pgm gene, rendering the bacterium incapable of synthesizing a key enzyme
in the metabolism of bacterial sugars. A live vaccine for immunization,
prophylaxis or treatment of brucellosis comprises such a bacterium,
either lyophilized or in a pharmaceutical vehicle. Nucleotide sequence
fragments having the aforementioned deletion are disclosed, with methods
for making them.