Moraxella catarrhalis is a type of bacteria commonly found in the human respiratory tract. It is a gram-negative, aerobic organism that can be part of the normal flora in healthy individuals. However, it can also cause infections, particularly in people with weakened immune systems or underlying respiratory conditions. This bacterium is known to be associated with various illnesses, including otitis media (middle ear infections) and sinusitis. It can also lead to more serious respiratory infections, especially in patients with chronic obstructive pulmonary disease (COPD). Treatment typically involves antibiotics, although some strains may show resistance.