The Respiratory Pathogen Moraxella catarrhalis Adheres to Epithelial Cells by Interacting with Fibronectin through Ubiquitous Surface

Moraxella catarrhalis ubiquitous surface protein (Usp) A1 has been reported to bind fibronectin and is involved in adherence. In this study, using M. catarrhalis mutants derived from clinical isolates, we show that both UspA1 and UspA2 bind fibronectin. Recombinant truncated UspA1/A2 proteins, together with smaller frag-ments spanning the entire molecule, were tested for binding to fibronectin. Both UspA1 and UspA2 bound fibronectin, and the fibronectin-binding domains were located within UspA1299–452 and UspA2165–318. These 2 truncated proteins inhibited binding of M. catarrhalis to Chang conjunctival epithelial cells to an extent similar to that by anti-human fibronectin antibodies. Our observations show that both UspA1 and UspA2 are involved in adherence to epithelial cells via cell-associated fibronectin. The biologically active sites within UspA1299–452 and UspA2165–318 have therefore been suggested to be potential candidates to be included in a future vaccine against M. catarrhalis. Moraxella catarrhalis is a leading bacterial cause of acute otitis media in children, after Streptococcus pneumoniae and Haemophilus influenzae [1–3]. It is also a common cause of sinusitis and lower respiratory tract infections in adults with chronic obstructive pulmonary diseas