Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative diplococcus.
Can colonize the upper respiratory tract in humans. Most commonly associated with upper respiratory tract infections such as sinusitis and otitis media. Associated with lower respiratory tract infections (i.e pneumonia) and other systemic infections in immunocompromised hosts.
Upper respiratory tract infection
Pneumonia in immunocompromised hosts
Septic arthritis (rare)