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Infection and Immunity, April 2000, p. 2024-2033, Vol. 68, No. 4
Department of Microbiology and Immunology,
UCLA School of Medicine,1 and Molecular
Biology Institute,2 University of California,
Los Angeles, California 90095-1747
Received 7 September 1999/Returned for modification 15 November
1999/Accepted 28 December 1999
Fimbriae are filamentous, cell surface structures which have been
proposed to mediate attachment of Bordetella species to respiratory epithelium. Bordetella bronchiseptica has four
known fimbrial genes: fim2, fim3,
fimX, and fimA. While these genes are unlinked
on the chromosome, their protein products are assembled and secreted by
a single apparatus encoded by the fimBCD locus. The
fimBCD locus is embedded within the fha operon,
whose genes encode another putative adhesin, filamentous hemagglutinin
(FHA). We have constructed a Fim
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Copyright © 2000, American Society for Microbiology. All rights reserved.
Role of Bordetella bronchiseptica
Fimbriae in Tracheal Colonization and Development of a Humoral
Immune Response
B. bronchiseptica strain, RB63, by introducing an in-frame deletion extending from fimB through fimD. Western blot
analysis showed that RB63 is unable to synthesize fimbriae but is
unaffected for FHA expression. Using this mutant, we assessed the role
of fimbriae in pathogenesis in vitro and in vivo in natural animal
hosts. Although RB63 was not significantly defective in its ability to adhere to various tissue culture cell lines, including human laryngeal HEp-2 cells, it was considerably altered in its ability to cause respiratory tract infections in rats. The number of
fimBCD bacteria recovered from the rat trachea at 10 days postinoculation was significantly decreased compared to that of
wild-type B. bronchiseptica and was below the limit of
detection at 30 and 60 days postinoculation. The number of bacteria
recovered from the nasal cavity and larynx was not significantly
different between RB63 and the wild-type strain at any time point. The
ability of fimbriae to mediate initial attachment to tracheal tissue
was tested in an intratracheal inoculation assay. Significantly fewer
RB63 than wild-type bacteria were recovered from the tracheas at
24 h after intratracheal inoculation. These results demonstrate
that fimbriae are involved in enhancing the ability of B. bronchiseptica to establish tracheal colonization and are
essential for persistent colonization at this site. Interestingly, anti-Bordetella serum immunoglobulin M (IgM) levels were
significantly lower in animals infected with RB63 than in animals
infected with wild-type B. bronchiseptica at 10 days
postinoculation. Even at 30 days postinoculation, RB63-infected animals
had lower serum anti-Bordetella antibody titers in general.
This disparity in antibody profiles suggests that fimbriae are also
important for the induction of a humoral immune response.
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, UCLA School of Medicine, Center for the Health Sciences, 10833 LeConte Ave., Los Angeles, CA 90095-1747. Phone:
(310) 206-0319. Fax: (310) 206-3865. E-mail:
pcotter{at}ucla.edu.
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