Moraxella catarrhalis (Mca) is a kind of gram-negative diplococcus which can exist in the respiratory tract of the human. It could be a non-symptom diplococcus on the health people. Otitis media occurs when the Mca reaches the middle ear along the eustachian tube. Sometimes the patients could suffer from the acute exacerbation of chronic obstructive pulmonary disease or pneumonia due to lung lesions caused by Mca. Little is known about the pathogenesis of the Mca, which leads to an incomplete understanding of its pathogenicity. This review aims to clarify the relationships between the Mca and the related diseases and the mechanism of the significant virulence factors. We hope to raise awareness of Mca and also provide some ideas for clinical diagnosis of relevant diseases it caused.

Moraxella catarrhalis; Otitis media; Lung diseases, obstructive; Pathogenicity; Virulence factors