Brucella abortusRB51 Induces Protection in Mice Orally Infected with the Virulent StrainB. abortus2308

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Abstract
Brucellae are gram-negative, facultative intracellular bacteria which are one of the most common causes of abortion in animals. In addition, they are the source of a severe zoonosis. In this trial, we evaluated the effect of oral inoculation ofBrucella abortusRB51 in mice against a challenge infection withB. abortus2308. First, we showed that a gastric acid neutralization prior to the oral inoculation contributed to a more homogeneous and consistent infection with both vaccine strainB. abortusRB51 and virulent strainB. abortus2308. Successively, we assessed the clearance and the immune response following an oral infection withB. abortusRB51. Oral inoculation gave a mild infection which was cleared 42 days after infection, and it induced a delayed humoral and cell-mediated immune response. Finally, we immunized mice by oral inoculation withB. abortusRB51, and we challenged them with the virulent strainB. abortus2308 by an oral or intraperitoneal route 42 days after vaccination. Oral inoculation ofB. abortusRB51 was able to give protection to mice infected with the virulent strainB. abortus2308 by the oral route but not to mice infected intraperitoneally. Our results indicate that oral inoculation of mice withB. abortusRB51 is able to give a protective immunity against an oral infection with virulent strains, and this protection seems to rely on an immune response at the mucosal level.