Recommendations for the description of species and biotypes of the genus Brucella.

The properties of the genus Brucella are summarized and recommendations made for the definition of species and biotypes within the genus. In the first instance it is recommended that the classification of an organism as a member of the genus should be based on the following criteria: gramnegative coccobacillary morphology, a G + C content for the DNA of 56-58 moles %, a minimum of 90% homology with the DNA of reference strains in hybridization tests, disk electrophoretograms of acid-phenol soluble proteins of identical pattern to reference strains, a cytochrome C absorption spectrum with absorption maxima between 522-530 nm and 552-560 nm, extensive serological cross-reactions of intra-cellular antigens with those of reference strains. Supporting evidence is obtained from cultural, biochemical and pathogenic properties, although variations in these occur within the genus. Subdivision into species is dependent upon principal natural host, oxidative metabolic pattern and phage sensitivity. Classification into biotypes is dependent upon CO2 requirement, H2S production, dye sensitivity and reaction with monospecific antisera to A and M antigens. It is recommended that any organism proposed as a new member of the genus should have characters which approximate the ranges quoted. In all cases comparisons should be made with the established reference/neotype strains.