Burkholderia cenocepacia is an important respiratory pathogen in persons with cystic fibrosis (CF). Recent studies indicate that B. cenocepacia survives within macrophages and airway epithelial cells in vitro by evading endosomelysosome fusion. We investigated the role of a plasmid-encoded type IV secretion system in the intracellular survival, replication, and processing of B. cenocepacia. Both a wild-type strain (K56-2) and its type IV secretion system mutant (designated LC101) entered and replicated in CF airway epithelial cells and monocyte-derived macrophages. However, significantly more intracellular K56-2 than LC101 bacteria were found in both cell types at 24 h postinfection. Colocalization of bacteria with markers of the classical endocytic pathway indicated that although both K56-2 and LC101 reside transiently in early endosomes, a greater proportion of the mutant bacteria are targeted to lysosomal degradation. In contrast, wild-type bacteria escape from the classical endocytic pathway and traffic to the endoplasmic reticulum, where they replicate. Our results show that the intracellular processing of B. cenocepacia is similar in both professional and nonprofessional phagocytes and that a functional plasmid-encoded type IV secretion system contributes to the survival and replication of B. cenocepacia in eukaryotic cells.

Purified rat intestinal mucin was used as a model mucin to study the binding of Escherichia coli serotype 0157:H7, a human pathogen associated with outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. Of six 0157:H7 strains, only one strain (designated CL-49) bound to rat (and other) intestinal mucins by a specific and saturable process. Binding was observed only after the bacteria were serially passaged to promote the expression of type 1 pili (fimbriae). Several other type 1-piliated E. coli strains, however, did not bind to mucin. Binding of E. coli CL-49 was inhibited by D-mannose and short oligomannosyl derivatives, particularly Man-a-1,3-Man, Man-a-1,2-Man, and Man-a-1,3-Man- ,-1,4-N-acetylglucosamine. Other inhibitors of binding included p-nitrophenol (10-4M), heating at 60°C (to remove pili), an antibody to type 1 pili, and purified type 1 pili of E. coli CL-49 used as hapten inhibitors. A comparison of the hydrophobicity of piliated E. coli CL-49 with other type 1-piliated E. coli strains indicated that the former strain was much more hydrophobic than the others. These findings indicate that highly purified intestinal mucins possess specific mannosyl receptor sites for bacterial type 1 pili on E. coli CL-49, but that strong hydrophobic interactions between the mucin and the pili stabilize the mannose-dependent binding process. We speculate that the mucin receptors for type 1 pili reside in oligosaccharides of the 118-kilodalton "link" glycopeptide, since this is the only mucin component known to contain mannose.

In previous experiments, we have shown that isolates of Pseudomonas cepacia from sputa of patients with cystic fibrosis (CF), particularly those with severe lung infection, exhibited specific binding to purified respiratory or intestinal mucins (U.