Abstract
In making a study, with Dr. J. Traum, on the causes of discrepancies occasionally encountered in testing cattle sera for Br. abortus agglutinins, it was noticed that different lots of antigens from certain strains gave varying reactions with the same sera. It was necessary to conclude that the antigen varied because all negative sera gave similar reactions on such lots of antigen and these same sera gave only definite negative results with antigens from many other strains of Br. abortus.
To determine the character of the variation mentioned above, glucose-glycerine agar plates were dallied with suspensions of the growth to be used for antigens. At the end of a 4-day incubation period, colonies of 2 distinct and constant types were present. One is the usual Br. abortus colony, moist, clear and only slightly granular. By transmitted light, these colonies show a blue-green florescence. The second type of colony is opaque, very definitely granular, and grows more rapidly than does the clear type. Subcultures from the clear type are readily suspended in salt solution and remain suspended for several days. The opaque type, on the other hand, is suspended with difficulty and spontaneously agglutinates within 24 to 48 hours. The subcultures of the opaque type have remained free of clear type colonies through several transplant generations. The clear cultures, however, continue to produce an occasional opaque colony even after several platings.
Plates made from 23 stock strains of Br. abortus showed none of these strains to be entirely free of both types, although the ratio of opaque to clear colonies varied over a wide range.
Get full access to this article
View all access options for this article.