The head of Bartonella adhesin A is crucial for host cell interaction of Bartonella henselae.

Human pathogenic Bartonella henselae cause cat scratch disease and vasculoproliferative disorders (e.g. bacillary angiomatosis). Expression of Bartonella adhesin A (BadA) is crucial for bacterial autoagglutination, adhesion to host cells, binding to extracellular matrix proteins and proangiogenic reprogramming via activation of hypoxia inducible factor (HIF)-1. Like the prototypic Yersinia adhesin A, BadA belongs to the class of trimeric autotransporter adhesins and is constructed modularly consisting of a head, a long and repetitive neck-stalk module and a membrane anchor. Until now, the exact biological role of these domains is not known. Here, we analysed the function of the BadA head by truncating the repetitive neck-stalk module of BadA (B. henselae badA(-)/pHN23). Like B. henselae Marseille wild type, B. henselae badA(-)/pHN23 showed autoagglutination, adhesion to collagen and endothelial cells and activation of HIF-1 in host cells. Remarkably, B. henselae badA(-)/pHN23 did not bind to fibronectin (Fn) suggesting a crucial role of the deleted stalk domain in Fn binding. Additionally, the recombinantly expressed BadA head adhered to human umbilical vein endothelial cells and to a lesser degree to epithelial (HeLa 229) cells. Our data suggest that the head represents the major functional domain of BadA responsible for host adhesion and angiogenic reprogramming.

Use of Bartonella adhesin A (BadA) immunoblotting in the serodiagnosis of Bartonella henselae infections.

Bartonella henselae causes a variety of human diseases (e.g. cat scratch disease and the vasculoproliferative disorders, bacillary angiomatosis and peliosis hepatis). The laboratory diagnosis of B. henselae infections is usually based on the detection of anti-B. henselae antibodies by an indirect immunofluorescence assay (IFA) which, unfortunately, suffers from a significant amount of cross-reactivity and hence is prone to deliver false-positive results. In this pilot study, we evaluated the use of a potential two-step serodiagnosis of B. henselae infections by combining IFA and anti-Bartonella adhesin A (BadA) immunoblotting. Our data revealed that approximately 75% of the IFA-positive sera of patients with a suspected B. henselae infection reacted specifically with BadA but only approximately 25% of the IFA-negative sera of healthy blood donors. Although Yersinia adhesin A (YadA) is structurally closely related to BadA, no cross-reactivity of sera from patients suffering from a Yersinia enterocolitica or Y. pseudotuberculosis infection with BadA was detected in immunoblotting. Unfortunately, recombinantly expressed BadA domains (head, connector, stalk fragment) were not suitable for immunoblotting. Finally, the best resolution for full-length BadA immunoblotting was obtained when whole cell lysates of B. henselae were separated using continuous 4-15% sodium dodecyl sulfate polyacrylamide gels. In summary, our results show that BadA antibodies are detectable in the sera of B. henselae-infected patients and, therefore, this pilot study suggests to include BadA immunoblotting in the laboratory diagnosis of B. henselae infections.