DELETION OF PURE ATTENUATES BRUCELLA-MELITENSIS INFECTION IN MICE

We previously showed that a purE mutant (Delta purE201) of Brucella me litensis 16M is attenuated for growth in cultured human monocytes (E. S. Drazek, H. H. Houng, R. M. Crawford, T. L. Hadfield, D. L. Hoover, and R. L. Warren, Infect. Immun. 63:3297-3301, 1995). To determine if this strain is attenuated in animals, we compared the growth of the De lta purE201 mutant with that of strain 16M in BALB/c mice. The number of bacteria in the spleen and spleen weight peaked for both strains be tween 1 and 2 weeks postinfection (p.i.), though the number of Delta p urE201 cells was significantly less than the number of 16M cells recov ered from the spleens of infected mice. During the next 6 weeks, Delta purE201 was essentially eliminated from infected mice (three of five mice sterile; < 100 CFU in two of five mice at 8 weeks p.i.), whereas bacteria persisted at a high level in the spleens of 16M-infected mice (about 10(6) CFU per spleen). The number of bacteria in the livers an d lungs of mice infected with either strain paralleled those in the sp leen. Mice infected with 16M had a strong inflammatory response, devel oping dramatic and prolonged splenomegaly (five to eight times normal spleen weight) and producing serum interleukin-6. In contrast, mice in fected with Delta purE201 developed only mild, transient splenomegaly at 1 week p.i. and produced no interleukin-6 in their serum. We furthe r characterized the host response to infection by measuring changes in immune spleen cell populations by flow cytometry. CD4- and CD8-positi ve lymphocytes declined by 1 week in both experimental groups, while M AC-1-positive cells increased. T-cell subpopulations remained low or d eclined further, and MAC-1 cells increased to three times normal level s during 8 weeks of infection with 16M but returned to normal by 4 wee ks after infection with Delta purE201. These results document infectiv ity and attenuation of Delta purE201 and suggest that it should be fur ther evaluated as a potential vaccine.