Role of Burkholderia Cenocepacia Adhesin, AdhA, in Cystic Fibrosis Infections

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DESCRIPTION (provided by applicant): Cystic fibrosis (CF) is an autosomal recessive disease that affects approximately 1:2700 live births. In the United States there are about 30,000 individuals living with CF. The disease manifests as multi-organ dysfunction with the most common cause of death is respiratory failure due to chronic lung infections. Pseudomonas aeruginosa is responsible for most lung infections, affecting >80% of CF patients; however, bacteria belonging to the Burkholderia cepacia complex (Bcc) have emerged as life-threatening respiratory pathogens. While infecting less than 10% of CF patients, Bcc is noteworthy for being strongly associated with increased rates of morbidity and mortality, capable of patient-to-patient spread, and a syndrome of acute bacteremia and pneumonia, referred to as "cepacia syndrome". Among the species of the Bcc, Burkholderia cenocepacia "epidemic" strains are responsible for a disproportionate degree of CF lung infections and are more likely to cause severe infections, inter-patient spread, and greater rates of mortality. B. cenocepacia belonging to the ET12 epidemic lineage are especially problematic in CF. This lineage is distinctive in the expression of both a cable pilus and an associated 22-kDa adhesin (AdhA). We have previously shown that AdhA is localized along the shaft of the cable pilus and mediates binding to and invasion of host cells. Mutants that lack either the cable pilus or AdhA fail to bind, damage, or transmigrate across squamous epithelial cells, indicating the importance of these structures in pathogenesis. Cable pili are assembled and secreted via the typical chaperone-usher pathway. In contrast, the 22-kDa AdhA adhesin is contained within an open reading frame that encodes a >278 kDa protein that has at least 12 large repeated sequences. This protein shows homology to putative adhesin proteins in both Gram-negative and Gram-positive bacteria. AdhA appears to be unique among this family of proteins in that it is processed to a much smaller form and is associated with a cell-surface appendage. Downstream of the adhA gene are genes encoding proteins homologous to a type I secretion apparatus. We hypothesize the AdhA adhesin plays an important role in the pathogenesis of B. cenocepacia lung infections. Therefore, in the first specific aim of this two-year exploratory grant, we will determine the contribution of AdhA to virulence by comparing a wild type ET12 lineage strain to an isogenic AdhA mutant, which we have previously characterized, in complementary murine models that highlight different stages of Bcc respiratory infection. In the second specific aim, we will determine whether AdhA is secreted by a type I secretion apparatus, encoded by the genes downstream of the adhA gene. Findings from these experiments will define the role of this adhesin molecule in virulence as well as the steps in the secretion of AdhA. These studies represent a logical first step in the development of reagents to inhibit these interactions and thereby the pathogenesis of Bcc infections in patients with CF. PUBLIC HEALTH RELEVANCE: This grant focuses on the adhesin molecule, AdhA, of the bacteria Burkholderia cenocepacia, which is an emerging lung pathogen in cystic fibrosis patients. In particular, we will (1) compare adhesin mutants, which we have already constructed and characterized, to the wild type strain, in mice models of infection that assess different aspects of pathogenesis, and (2) determine how this unusual protein adhesin is secreted from B. cenocepacia. These experiments are the first steps in developing strategies to prevent the life threatening infections caused by this bacterium.