An evaluation of a biphasic medium for the isolation of Brucella abortus from bovine tissues.

The isolation of virulent Brucella abortus from specimens taken from cattle was studied using culture in biphasic medium in which solid and liquid media were contained in the same flask and on solid medium in Petri plates. A total of 8638 specimens from 441 cattle, reactors to one or more of several serological tests or to an allergic test, were used. The specimens consisted of lymph nodes, udder, spleen, uterine caruncles, cotyledons, foetal tissues, foetal stomach contents and mammary secretions. Following maceration each specimen was inoculated into 2 flasks of biphasic medium one with 1 ml (Flask A) and the other with 2 ml (Flask B), and on to solid medium in one Petri plate. The biphasic medium and solid medium were shown to have equal ability to support the growth of B. abortus. The increased rate of detection in the biphasic medium was due to the increased volume of the inoculum used. Brucella were isolated from 1151 specimens. By direct plating on the solid medium 685 specimens were positive whereas Flask A positive for 961 specimens and Flask B for 1031 specimens. The success of the biphasic medium can be judged by the increase in the number of infected animals detected. Of the 150 infected cattle, both techniques identified 126 animals in common, 4 were identified only by the plate technique and 20 only by the biphasic technique. Culture on both solid medium and in biphasic medium is recommended for optimum results.