Degradation of host defence molecules by CF-related pathogens grown as biofilms

We investigated the ability of secreted bacterial proteinases from three pathogens [Burkholderia multivorans (Bm), Burkholderia cenocepacia (Bc), and Pseudomonas aeruginosa (Pa)] involved in chronic bacterial infections in cystic fibrosis to degrade various host defence-related molecules. These included two endogenous proteinase inhibitors, secretory leukocyte proteinase inhibitor (rhSLPI) and alpha-1 antitrypsin (AAT); two relevant immunoglobulins, secretory IgA (sIgA) and IgG, and two proteins important in innate immunity, lactoferrin and lysozyme. Host defence-related molecules were co-incubated with cell-free supernatants from 48 hour biofilm cultures, grown on mucin-coated microplates, from all three pathogens under investigation (six isolates from each species). No degradation of AAT, sIgA, IgG, and lactoferrin was observed for any of the organisms. Of the 18 isolates tested, only one demonstrated the ability to degrade lysozyme. This was an environmental isolate of Pa which was included as a comparison for the predominantly clinically relevant isolates used in the study. In contrast, all isolates of Bm (n = 4) and Pa (n = 4) were able to degrade rhSLPI however, out of five bacterial isolates tested for Bc only two demonstrated a limited ability to degrade the molecule with >95% of the protein band still remaining intact at the end of the experiment. This study demonstrates that the majority of the host defence molecules investigated are resistant to degradation by bacterial proteinases from Bm, Bc and Pa when grown as a biofilm. However, rhSLPI was vulnerable to significant degradation which could result in aberrant serine proteolysis in regions of the lungs containing biofilm growth.