830 BRUCELLA 



however, many of whom have used different media, are so diflScult to summarize, 

 that we shall content ourselves with giving references to some of the more important 

 papers on this subject (Henry 1928, 1933, Plastridge and McAlpine 1930, Marshall 

 and Jared 1930, 1931, Morales-Otero 1931, Grumbach and Grillichess 1932). The 

 growth of smooth and rough forms in the presence of dyes appears to be very much 

 the same, but there is some evidence that the S — > R variation may be accom- 

 panied by a decrease in biochemical activity, particularly in the production of HjS. 

 Though it is true that some rough abortus and American suis strains still produce 

 HjS, it is equally true that many do not. Since practically all freshly isolated 

 smooth strains produce HjS, it seems not improbable that the loss of this property 

 on continued subcultivation is a manifestation of the S — > R. variation. 



Classification and Identification. — ^As has already been pointed out, the inclusion 

 of Br. tularensis in the Brucella group is largely tentative. This organism may 

 be distinguished from the other three members on the basis of morphological, 

 cultural, biochemical, antigenic, and pathogenic properties. 



The main difficulty lies in distinguishing between Br. melitensis, Br. abortus, 

 and Br. suis. This difficulty is accentuated by the fact that within each species 

 there are a number of sub-types differing from one another in minor respects 

 and approaching closely to the sub-types of adjacent species (see Meyer and Zobell 

 1932, Wilson 1933). These sub-types are often associated with some special 

 topographical distribution. Melitensis strains, for example, from Malta, may differ 

 from those from Palestine or from the South of France. Southern Rhodesian 

 abortus strains differ from European or American strains. The American suis 

 strains differ from the Danish strains, and so on. For purposes of identification, 

 therefore, the fullest possible examination is required, and no strain should be 

 definitely allocated to a particular species without a careful study by all available 

 bacteriological methods, including COj-sensitivity, growth in the presence of dyes, 

 H2S formation, antigenic analysis, and if possible virulence. Once the infecting 

 type has been firmly established, help is often afforded by a knowledge of the animal 

 source and country of origin. For instance, in this country Br. suis has never 

 been found, and Br. melitensis has been observed only once among cattle on a 

 small number of farms in the Midlands (see Duke 1940, Wilson 1940), so that 

 any indigenous strain of Brucella isolated from man, horses, dogs, or cattle, is 

 probably of the abortus type. In any country, strains isolated from sheep or 

 goats are usually of the melitensis type, from pigs of the suis type, from cattle, 

 horses, and dogs of the abortus type, while strains isolated from man usually belong 

 to that type which is most prevalent in the neighbouring animal population. 

 Exceptions, however, are not uncommon, so that too much reliance should not 

 be placed on this particular aid to identification. 



Though there are numerous sub-types of Brucella with particular geographical 

 locations, indicating that the members of the group are relatively labile and respon- 

 sive to environmental changes, no one has yet succeeded in converting one type into 

 another. Even prolonged residence of the melitensis and suis types in cows, and of 

 the abortus type in sheep, seems to have no effect on the type of organism introduced. 

 For practical purposes, therefore, the main types can be regarded as constant. 

 Table 53 summarizes the chief differential features of members of this group. 

 (Useful reviews of the Brucella group will be found in papers by Kristensen 1931, 

 Taylor, Lisbonne, and Roman 1932, Zeller 1933, Habs 1933, Wilson 1933, Huddleson 

 1934, Thomsen 1934, Olin and Lindstrom 1934.) 



