The Burkholderia cepacia complex (Bcc) is a collection of genetically distinct but phenotypically similar bacteria that are divided into at least nine species. Bcc bacteria are found throughout the environment, where they can have both beneficial and detrimental effects on plants and some members can also degrade natural and man-made pollutants. Bcc bacteria are now recognized as important opportunistic pathogens that can cause variable lung infections in cystic fibrosis patients, which result in asymptomatic carriage, chronic infection or 'cepacia syndrome', which is characterized by a rapid decline in lung function that can include invasive disease. Here we highlight the unique characteristics of the Bcc, focusing on the factors that determine virulence.

Burkholderia cenocepacia is an opportunistic pathogen that can cause severe lung infections in cystic fibrosis patients. To understand the contribution of B. cenocepacia flagella to infection, a strain mutated in the major flagellin subunit, fliCII, was constructed in B. cenocepacia K56-2 and tested in a murine agar bead model of lung infection. C57/BL6 mice infected with ϳ10 8 wild-type K56-2 bacteria exhibited 40% mortality after 3 days, whereas no mortality was noted in mice infected with the fliCII mutant. Among the mice surviving the infection with either strain, there was no significant difference in the bacterial loads in the lungs and spleen, bacteremia, weight loss, or infiltration of immune effector cells at 3 days postinfection. Similar results were observed at 24 h, prior to expression of the lethality phenotype. KC, a murine interleukin-8 (IL-8) homolog, was elevated in both the bronchoalveolar lavage fluid and serum of mice infected with the wild type compared to the fliCII mutant at 24 h, suggesting that flagella stimulated host cells. To demonstrate that flagella contributed to these responses, the interaction between B. cenocepacia and Toll-like receptor 5 (TLR5) was investigated. Infection of HEK293 cells with heat-killed wild-type K56-2, but not infection with the fliCII mutant, resulted in both NF-B activation and IL-8 secretion that was dependent upon expression of TLR5. Together, these results demonstrate that B. cenocepacia flagella contribute to virulence in an in vivo infection model, and that induction of host immune responses through interaction with TLR5 may contribute to its overall pathogenic potential.

Acute pneumonias and corneal infections due to Pseudomonas aeruginosa are typically caused by lipopolysaccharide (LPS)-smooth strains. In cystic fibrosis patients, however, LPS-rough strains of P. aeruginosa, which lack O antigen, can survive in the lung and cause chronic infection. It is not clear whether an LPS-rough phenotype affects cytotoxicity related to the type III secretion system (TTSS). We previously reported that interruption of the galU gene in P. aeruginosa results in production of a rough LPS and truncated LPS core. Here we evaluated the role of the galU gene in the pathogenesis of murine lung and eye infections and in cytotoxicity due to the TTSS effector ExoU. We studied galU mutants of strain PAO1, of its cytotoxic variant expressing ExoU from a plasmid, and of the inherently cytotoxic strain PA103. The galU mutants were more serum sensitive than the parental strains but remained cytotoxic in vitro. In a corneal infection model, the galU mutants were significantly attenuated. In an acute pneumonia model, the 50% lethal doses of the galU mutants were higher than those of the corresponding wild-type strains, yet these mutants could cause mortality and severe pneumonia, as judged by histology, even with minimal systemic spread. These findings suggest that the galU gene is required for corneal infection and for efficient systemic spread following lung infection but is not required for infection confined to the lung. Host defenses in the lung appear to be insufficient to control infection with LPS-rough P. aeruginosa when local bacterial levels are high.

The influence of solution pH (in the range 3–9) on the adsorption of polyacrylic acid (PAA) on the mixed silica–alumina surface (SA-3: SiO2 97 %–Al2O3 3 % and SA-96: SiO2 4 %–Al2O3 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.

Burkholderia cenocepacia strains expressing both cable (Cbl) pili and the 22-kDa adhesin bind to cytokeratin 13 (CK13) strongly and invade squamous epithelium efficiently. It has not been established, however, whether the gene encoding the adhesin is located in the cbl operon or what specific contribution the adhesin and Cbl pili lend to binding and transmigration or invasion capacity of B. cenocepacia. By immunoscreening an expression library of B. cenocepacia isolate BC7, we identified a large gene (adhA) that encodes the 22-kDa adhesin. Isogenic mutants lacking expression of either Cbl pili (cblA or cblS mutants) or the adhesin (adhA mutant) were constructed to assess the individual role of Cbl pili and the adhesin in mediating B. cenocepacia binding to and transmigration across squamous epithelium. Relative to the parent strain, mutants of Cbl pili showed reduced binding (50%) to isolated CK13, while the adhesin mutant showed almost no binding (0 to 8%). Mutants lacking either cable pili or the adhesin were compromised in their ability to bind to and transmigrate across the squamous epithelium compared to the wild-type strain, although this deficiency was most pronounced in the adhA mutant. These results indicate that both Cbl pili and the 22-kDa adhesin are necessary for the optimal binding to CK13 and transmigration properties of B. cenocepacia.