Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 19, 1997
Publication Date: N/A
Interpretive Summary: Bordetella bronchiseptica is one of the infectious agents of atrophic rhinitis and pneumonia in swine. These diseases are extremely widespread and costly in the swine production industry, both in the United States and worldwide. Although vaccines are available, they provide only limited protection from disease. A better understanding of how B. bronchiseptica initiates infection in swine will greatly assist the development of more efficacious vaccines. The ability of this organism to bind to swine nasal epithelium is a critical, but poorly understood, step in the initiation of infection. In this study we have characterized the ability of B. bronchiseptica to bind to ciliated epithelial cells isolated from 1-week old piglets. We found that bacteria grown under conditions expected to be encountered during natural infection possess a heightened ability to bind to swine epithelial cells. Such bacteria produce a previously undescribed attachment factor that is not produced when the organisms are grown under the artificial conditions used in the laboratory. This observation suggests that one of the reasons for the poor efficacy of currently available vaccines is that bacteria grown under standard laboratory conditions for vaccine production may not be synthesizing the critical proteins required to induce protective immunity. We also report preliminary characterization of the attachment factor. This report and subsequent isolation and identification of the attachment factor will provide important new information for the design of improved vaccines, ultimately benefiting the producer and the swine industry.
Technical Abstract: The ability of Bvg**- -phase and Bvg**+ -phase Bordetella bronchiseptica swine isolates, grown under modulating or nonmodulating conditions, to adhere to swine ciliated nasal epithelial cells was determined. When virulent strains were cultivated at 37 deg C in the Bvg**+ phase, numerous adherent bacteria were observed (approx. 8 bacteria per cell, depending on strain used). However, when such strains were grown under modulating conditions (23 deg C), a significant incsrease in the level of attachment was seen, suggesting that B. bronchiseptica produces a bvg-repressed adhesion under these conditions. Genetically bvg**- strains, including an isogenic bvgS**- mutant, adhered minimally. Western blots indicated that two putative B. brochiseptica adhesions, filamentous hemagglutinin and pertactin, were not detectable in cultures displaying the highly adherent phenotype. Several proteins apparent in Western blots using bacterial extracts enriched in outer membrane proteins derived from B. bronchiseptic grown at 23 deg C were not present in similar extracts prepared from an isogenic bvgS**- mutant grown at 23 deg C or from the parent strain grown at 37 deg C. Adherence of bacteria cultivated at 23 deg C was almost completely abolished by pretreatment of organisms at 60 deg C; adherence was reduced by 57% when bacteria were pretreated with pronase E. Temperature shift experiments revealed that the heightened level of adhesion that occurs following growth at 23 deg C was maintained for up to 18 hours when bacteria were subsequently inculbated at 37 deg C. We propose that a Bvg-repressed adhesin, expressed only by modulated bvg**+ strains of B. bronchiseptica, may play a key role in the initial colonization of naturally infected swine.