[Construction and characterization of a brucella suis S2 strain with a chloramphenicol resistance marker].

Vaccination has not been used widely because of the interference in the discrimination between infected and vaccinated animals in immune-screening procedures. In the present study, chloramphenicol resistance gene (Cm(r)) was cloned into the genomic DNA of brucella suis S2 strain by homologous recombination with knocking out the WbkC gene, and obtained the recombinant rS2-WbkC. Further study confirmed that rS2-WbkC was conversed into rough-phenotype form smooth-phenotype. The recombinant keeps the ability to chloramphenicol resistance after 25 passages in tryptic soy agar (TSA). Mice tests showed rS2-WbkC offered similar protection to S2 strain, but more safe than S2. Serum collected form rS2-WbkC immunized mice could be easily distinguished from antiserum produced by smooth-phenotype brucella abortus. In view of these result, rS2-WbkC is a promising candidate for vaccine strain.