Interaction of Bacteroides fragilis and Bacteroides thetaiotaomicron with the kallikrein–kinin system

Abstract

Many bacterial pathogens interfere with the contact system (kallikrein–kinin system) in human plasma. Activation of this system has two consequences: cleavage of high-molecular-mass kininogen (HK) resulting in release of the potent proinflammatory peptide bradykinin, and initiation of the intrinsic pathway of coagulation. In this study, two species of the Gram-negative anaerobic commensal organismBacteroides, namelyBacteroides fragilisandBacteroides thetaiotaomicron, were found to bind HK and fibrinogen, the major clotting protein, from human plasma as shown by immunoelectron microscopy and Western blot analysis. In addition, theseBacteroidesspecies were capable of activating the contact system at its surface leading to a significant prolongation of the intrinsic coagulation time and also to the release of bradykinin. Members of the genusBacteroideshave been known to act as opportunistic pathogens outside the gut, withB. fragilisbeing the most common isolate from clinical infections, such as intra-abdominal abscesses and bacteraemia. The present results thus provide more insight into howBacteroidesspecies cause infection.