An isolated and purified non-denatured outer membrane protein CD which is that of or corresponds to that isolatable from a Moraxella strain, particularly M. catarrhalis, is isolated from a bacterial strain by fractionating a cell lysate formed by disrupting a cell mass of the bacterial strain by centrifugation to provide a pellet and a discard supernatant containing a large proportion of soluble bacterial proteins. The pellet is selectively extracted to remove the remaining soluble proteins, the membrane proteins other than CD and other contaminants such as lipopolysaccharide and phospholipids. The remaining CD-containing pellet is dispersed and solubilized and then fractionated by centrifugation to remove the remaining cell debris. The CD protein is useful in diagnostic applications and immunogenic compositions, particularly for in vivo administration to a host to confer protection against disease caused by a bacterial pathogen that produces CD protein or produces a protein capable of inducing antibodies in a host specifically reactive with CD protein.
