Attenuation and immunogenicity of a Brucella abortus htrA cycL double mutant in cattle

PHE1 is a htrA cycL double gene deletion mutant of virulent Brucella abortu s strain 2308 (S2308) which has previously been evaluated in the murine and caprine models of bovine brucellosis. This report describes the results of studies conducted with this mutant in the natural bovine host. Six sexuall y mature, non-gravid heifers were inoculated via the conjunctival sac with 1x10(10) colony forming units (CFU) of either the parental S2308 or the htr A cycL gene deletion mutant, PHE1. At 4, 7 and 11 days post-inoculation. PH E1 was found to colonize the bovine host at lower levels than S2308. In a s econd experiment. eight heifers in mid-gestation were infected with 1x10(7) CFU of either strain via the conjunctival sac. The virulent S2308 caused a bortions or weak calves in 4/4 cows, while all four cows infected with PHE1 had healthy calves. Furthermore, PHE1 exhibited decreased resistance to ki lling by cultured bovine neutrophils and macrophages compared to the parent al strain. These studies demonstrate that the B. abortus htrA cycL gene del etion mutant PHE1 is highly attenuated in the bovine host when compared to the virulent parental S2308. (C) 2000 Elsevier Science B.V. All rights rese rved.