Selection of a Brucella vaccine strain of low residual virulence by chemical mutagenesis

Institute of Endemic Disease Control, Huhehot, Inner Mongolia * Institute of Epidemiology and Microbiology, PO Box 5, Changping, Beijing, China Received October 3, 1988 Accepted March 21, 1989 Following incubation of the oral vaccine Brucella suis strain 2 with diethyl sulphate (DES), a mutant designated strain S105 was selected by screening surviving bacteria for reduced virulence for mice. Strain 105 also showed low residual virulence for guinea-pigs and, unlike the parent strain, did not initiate abortion in pregnant sheep and goats after parenteral administration. Nevertheless, it was as effective as the parent strain in stimulating protective immunity to Brucella melitensis when given as an oral vaccine to sheep under both experimental and field conditions.