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Infect. Immun. doi:10.1128/IAI.00952-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A bile salt hydrolase of Brucella abortus contributes to the establishment of a successful infection through the oral route in mice

Instituto de Estudios de la Inmunidad Humoral (IDEHU, CONICET-UBA), Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, 1113 Buenos Aires, Argentina; Instituto de Investigaciones Biotecnológicas, Universidad Nacional de Gral. San Martín, 1650 San Martín, Argentina; Laboratorio de Inmunología, Departamento de Sanidad Animal y Medicina Preventiva, Facultad de Ciencias Veterinarias, Universidad Nacional del Centro de la Provincia de Buenos Aires, 7000 Tandil, Argentina; Laboratorio de Inmunogenética, Hospital de Clínicas "José de San Martín", Facultad de Medicina, Universidad de Buenos Aires, 1120 Buenos Aires, Argentina

^* To whom correspondence should be addressed. Email: pablobal{at}ffyb.uba.ar.

	Abstract

Choloylglycine hydrolase (CGH), a bile salt hydrolase, has been annotated in all the available genomes of Brucella species. We obtained the Brucella CGH in recombinant form and demonstrated in vitro its capacity to cleave glycocholate into glycine and cholate. B. abortus 2308 (wild-type) and its isogenic cgh deletion mutant exhibited a similar growth in tryptic soy broth in the absence of bile. In contrast, the growth of the cgh mutant was notably impaired by both 5% and 10% bile. Bile resistance of the complemented mutant was similar to that of the wild-type strain. In mice infected through the intragastric or the intraperitoneal route, splenic infection was significantly lower at 10 and 20 days p.i. in animals infected with the cgh mutant than in those infected with the wild-type strain. For both routes, no differences in spleen CFU were found between animals infected with the wild type strain or the complemented mutant. Mice immunized intragastrically with recombinant CGH mixed with cholera toxin (CGH/CT) developed a specific mucosal humoral (IgG and IgA) and cellular (IL-2) immune response. Fifteen days after challenge by the same route with live B. abortus 2308, splenic CFU counts were ten-fold lower in mice immunized with CGH/CT than in mice immunized with CT or PBS. This study shows that CGH confers Brucella the ability to resist the antimicrobial action of bile salts. The results also suggest that CGH may contribute to the ability of Brucella to infect the host through the oral route.