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Abstract
Burkholderia cepacia complex (Bcc) bacteria are a problematic group of microorganisms causing severe infections in patients with Cystic Fibrosis. In early stages of infection, Bcc bacteria must be able to adhere to and colonize the respiratory epithelium. Although this is not fully understood, this primary stage of infection is believed to be in part mediated by a specific type of adhesins, named trimeric autotransporter adhesins (TAAs). These homotrimeric proteins exist on the surface of many Gram negative pathogens and often mediate a number of critical functions, including biofilm formation, serum resistance and adherence to an invasion of host cells. We have previously identified in the genome of the epidemic clinical isolate B. cenocepacia J2315, a novel cluster of genes putatively encoding three TAAs (BCAM0219, BCAM0223 and BCAM0224). In this study, the genomic organization of the TAA cluster has been determined. To further address the direct role of the putative TAA BCAM0223 in B. cenocepacia pathogenicity, an isogenic mutant was constructed via insertional inactivation. The BCAM0223::Tp mutant is deficient in hemagglutination, affected in adherence to vitronectin and in biofilm formation and showed attenuated virulence in the Galleria mellonella model of infection. Moreover, the BCAM0223::Tp mutant also showed a significant reduction in its resistance to human serum as well as in adherence, but not in invasion of, cultured human bronchial epithelial cells. Altogether these results demonstrate that the BCAM0223 protein is a multifunctional virulence factor that may contribute to the pathogenicity of B. cenocepacia.
Highlights
The Burkholderia cepacia complex (Bcc) is a group of closely related Gram-negative bacteria found in the environment
We have previously conducted a computational analysis of the genome sequence of B. cenocepacia strain J2315 (ET12 lineage) and we identified a novel cluster of genes encoding 3 potential trimeric autotransporter adhesins (TAAs) (BCAM0219, BCAM0223 and BCAM0224), 1 outer membrane protein (BCAM0220), 2 sensor histidine kinases (BCAM0218, BCAM0227) and 3 transcriptional regulators (BCAM0221, BCAM0222, and BCAM0228) [13,28]
Our work has focused on one category of virulence determinants, the trimeric autotransporter adhesins (TAAs)
Summary
The Burkholderia cepacia complex (Bcc) is a group of closely related Gram-negative bacteria found in the environment. Bcc bacteria have emerged as highly problematic opportunistic pathogens causing severe respiratory infections in cystic fibrosis (CF) patients [1]. There are 17 species described as members of the Bcc complex. B. cenocepacia, B. multivorans and B. dolosa are those species that occur at a greater frequency and are problematic [2,3]. Colonized Bcc bacteria are transmitted among CF-patients and are extremely resistant to antimicrobial therapies [4]. In a subset of CF patients, lung infections with Bcc lead to declining lung function, with necrotising pneumonia and a fatal speticemia termed ‘‘cepacia syndrome’’ [5]
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