Role of Bordetella bronchiseptica Fimbriae in Tracheal Colonization and Development of a Humoral Immune Response

Abstract

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 ؊ 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.Specific attachment to host tissues is a crucial event in the initiation of bacterial infections. For many gram-negative bacteria, attachment has been shown to be mediated by filamentous polymeric protein cell surface structures called fimbriae (27). For instance, type IV pili of Neisseria species and Pseudomonas aeruginosa, as well as type I and pyelonephritis-associated P (Pap) pili of Escherichia coli, have been shown to serve as essential adhesins for colonization (for reviews, see references 1, 10, 22, 34, and 39).Bordetella pertussis and Bordetella bronchiseptica are small, aerobic, gram-negative bacteria that colonize the respiratory mucosa of humans and other mammals...

A Novel Sensor Kinase Is Required for Bordetella bronchiseptica To Colonize the Lower Respiratory Tract

“…Although several B. bronchiseptica mutants that are defective in colonization of the rat trachea have been identified (42,70), only strain RBX9, which contains a deletion of the gene encoding filamentous hemagglutinin (FHA), shows a complete lack of colonization by 10 days postinoculation, similar to the defect observed with RB50⌬plrS by day 7 postinoculation (13). FHA is an adhesin and immunomodulatory protein that has been shown to be indispensable for B. bronchiseptica colonization of the trachea, but not the nasal cavity (13,26).…”

“…Bacterial colonization of rat nasal septa and tracheae was determined by inoculating 1,000 CFU of overnight-grown (optical density at 600 nm [OD 600 ], between 2 and 3) wild-type or mutant B. bronchiseptica to the external nares of 3-to 4-week old female Sprague-Dawley rats (Charles River Laboratories, Wilmington, MA). At 7, 14, and 28 days postinoculation, the number of bacteria in the nasal septum and trachea was determined by plating aliquots of homogenized tissue on LB agar supplemented with streptomycin as described previously (42). Whole serum was collected by cardiac puncture from rats that had been infected for 28 days with the wild-type strain (RB50) for use as primary antibody in Western blot analyses.…”

“…Overnight-grown wild-type or mutant B. bronchiseptica (500,000 CFU) in a 50-l volume was inoculated directly into the trachea and lungs (26). At 1 hour, 4 days, 11 days, and 28 days postinoculation, the nasal septa, tracheae, and three right lung lobes were recovered and bacterial levels were determined by plating aliquots of tissue extracts on LB agar supplemented with streptomycin as described previously (42).…”

Bordetellafilamentous hemagglutinin plays a critical role in immunomodulation, suggesting a mechanism for host specificity

“…In vitro studies suggest that FHA functions as an adhesin (14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), and several binding domains have been identified. A heparin-binding domain promotes attachment to sulfated polysaccharides (29), a carbohydrate-recognition domain facilitates bacterial binding to ciliated respiratory epithelial cells and macrophages (30), and an arg-gly-asp (RGD) triplet interacts with the leukocyte-response integrin͞integrin-associated protein (LRI͞IAP) complex on monocytes͞macrophages, resulting in up-regulation of complement-receptor-3-binding activity (23) and, with very late antigen-5 on epithelial cells, stimulating the up-regulation of intercellular adhesion molecule-1 via an NF-B signaling pathway (19,31).…”

“…Animals were killed 14 and 28 d postinoculation, and colonization levels in the nasal cavity and trachea were determined as described in ref. 27. To deliver bacteria directly to the trachea, rats were inoculated intranasally with 5 ϫ 10 5 CFU delivered in 50 l. At 1 and 24 h postinoculation, nasal septa and tracheas were recovered, and the levels of colonization were determined (27).…”