Selective media for isolation of Brucella abortus strain RB51 $ Richard L. Hornsby a , Allen E. Jensen a , Steven C. Olsen a,* , Charles O. Thoen b a Zoonotic Diseases Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, 2300 Dayton Ave., Ames, IA 50010, USA b Department of Microbiology, Immunology, and Preventive Medicine, Iowa State University, Ames, IA 50011, USA Received 19 July 1999; received in revised form 20 December 1999; accepted 20 December 1999 Abstract Brucella abortus strain RB51 (SRB51) is the standard vaccine used to protect cattle against brucellosis and is currently being used to vaccinate bison in the United States (US). Currently available media for culture of Brucella have not been evaluated for their ability to support growth of SRB51. In this study, ®ve selective media for isolating brucellae, four commercially available media for gram-negative bacteria, and tryptose agar with 5% bovine serum (TSA) were compared to two SRB51 selective media developed in this study (rifampin brucellae medium (RBM), and malachite green brucellae medium (MGB)), for their ability to support growth and enhance recovery of SRB51. Four of the ®ve media currently used for isolation of brucellae and two of the four media used for other Gram-negative bacteria did not support growth of SRB51. Modi®ed Kuzdas and Morse (MKM), Brilliant Green, Skirrow's, RBM, and MGB supported growth of SRB51 in a manner similar to TSA. Recovery of SRB51 from tissues of SRB51-vaccinated bison was attempted on TSA, MKM, RBM, and MGB. From a total of 436 samples, SRB51 was isolated from 9.6, 4.3, 5.5, and 9.0% on TSA, MKM, RBM, or MGB media, respectively. Strain RB51 was recovered on only one medium (nine on TSA; three on RBM; and 9 on MGB) from 21 samples. Overgrowth of contaminating bacteria prevented potential detection of SRB51 from 9.4, 5.5, 0.07, and 5.9% of samples on TSA, MKM, RBM, or MGB, respectively. These data suggest that the use Veterinary Microbiology 73 (2000) 51±60 $ No endorsements are herein implied. Brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standards of the products, and the use of the names by USDA implies no approval of the products to the exclusion of others that may also be suitable. * Corresponding author. Tel.: 1-515-663-7230; fax: 1-515-663-7458. E-mail address: solsen@nadc.ars.usda.gov (S.C. Olsen) 0378-1135/00/$ ± see front matter Published by Elsevier Science B.V. PII:S0378-1135(00)00149-8