Involvement of Stenotrophomonas maltophilia Flagellin in Bacterial Adhesion to Airway Biotic Surfaces: An in Vitro Study

Stenotrophomonas maltophilia is an important opportunistic pathogen that affects immunocompromised individuals. In the present study its ability to adhere to mouse tracheal epithelial cells of BALB/c mice as well as to HEp-2 cells was evaluated. All the five clinical isolates used in this study were able to adhere to these biotic surfaces. The involvement of flagella in the adhesion process was evaluated by employing antiflagellin antibodies or flagellin as inhibitors of adhesion. To achieve this, flagellin C was purified from wild type clinical isolate (Sm2) that showed maximum adhesion in vitro. The molecular weight of pure preparation was 42 kDa on SDS-PAGE and antisera raised in rabbit against this preparation confirmed its purity on immunoblotting. The receptors were blocked by treatment of bacteria either with anti-flagellin or pretreatment of mouse trachea or HEp-2 cells with purified flagellin. Reduced bacterial adherence in presence of flagellin antisera and pure flagellin collectively confirmed the role of flagella in adhesion to biotic surfaces. However antiserum was more effective in reducing the adhesion probably due to its dual mode of action. It not only reduced the binding of adhesins on the flagella to specific receptors but also inhibited the motility of S. maltophilia. The inability of the bacterial colony to spread through agar containing antiserum confirmed the effect of antibodies on the motility of the bacterium. These evidences conclusively prove the involvement of flagella in the adhesion of S. maltophilia to biotic surfaces.