Effect of antibiotics contained in two Brucella selective media on growth of Brucella abortus

The MIC and the highest concentration enabling bacterial growth (CEG) of the antibiotics contained in two selective media were determined for Brucella abortus, B. melitensis, and B. ovis. The nalidixic acid and bacitracin contained in Farrell’s selective medium were responsible for the inhibitory effects observed. Most brucellae can be isolated in common basal media (1), but the use of nonselective media cannot be recommended for the primary isolation of brucellae because of the high number of overgrowing contaminants usually present in clinical veter-inary samples. Accordingly, selective media are necessary for the isolation of brucellae. Several selective media containing antibiotics and/or bacteriostatic dyes, either in combination or alone added to different basal media, have been described for Brucella abortus (3, 5, 7, 8) and B. ovis (2, 10). Farrell’s selective medium, developed for the isolation of B. abortus from milk (4), is also recommended for the isolation of B. melitensis (1), but its efficacy for this purpose has never been rigorousl