Moraxella catarrhalis

This student page has not been curated.

Classification

Kingdom: Bacteria Phylum: Proteobacteria Class: Gammaproteobacteria Order: Pseudomonadales Family: Moraxellaceae Genus: Moraxella Species: M. catarrhalis

Description and Significance

Moraxella catarrhalis is common cause of otitis media, which is inflammation of the inner ear. This bacteria commonly infects children Characteristics:

• non-motile
• gram-positive
• diplococcus
• aerobic
• oxidase-positive
• sticks to host cell using a trimeric autotransported adhesion (TAA)
• commonly resistant to penicillin, ampicillin, and amoxicillin

Structure, Metabolism, and Life Cycle

M. catarrhalis displays an endotoxin that is similar to many found in the Neisseria species, which play a role in the disease process. Some strains of M. catarrhalis exhibit fimbriae or pili, which help the cells adhere to the respiratory epithelium. Also, the cells express specific proteins that allow uptake for iron which act as receptors. M. Catarrhalis forms round opaque colonies on blood and chocolate agar, and the colonies can be slid around agar surfaces without being disrupted; this is called the "hockey puck sign". One interesting feature of the cellular structure of M. catarrhalis is the presence of trimeric autotransporter adhesins, which are essentially a type of virulence factor. These are structures of gram-negative bacteria that allow the cells to infect a host through a process called cell adhesion. Another term for trimeric autotransporter adhesins is oligomeric coiled-coil adhesins (OCAs).

Ecology and Pathogenesis

Moraxella catarrhalis is specifically a human pathogen and it can cause infection in immunocompromised hosts, such as HIV/AIDS patients. Also, it can colonize the upper respiratory tract in children and infants more easily than adults and cause pneumonia and sinusitis. Moraxella catarrhalis enters the nasopharynx and can invade numerous cell types, including bronchial epithelium, small airway epithelium, and type II alveolar pneumocytes. [3] It can migrate to the middle ear after it enters the nasopharnyx. It forms a biofilm in vitro, but it is not clear what the function of this biofilm is. The patient will experience symptoms of acute sinusitis, urethritis, septiciema, meningitis, maxillary sinusitis, conjunctivitis, and septic arthritis. Thie infection will cause exacerbation of chronic lung conditions [2].

References

[1] Bakri F, Brauer AL, Sethi S, Murphy TF. Systemic and mucosal antibody response to Moraxella catarrhalis following exacerbations of chronic obstructive pulmonary disease. J Infect Dis 2002;185:632-40. [2] Nicotra B, Rivera M, Luman JI, Wallace RJ.Branhamella catarrhalis as a lower respiratory tract pathogen in patients with chronic lung disease. Arch Intern Med1986;146:890-3. [3] Tolentino LF. Causes of Moraxella catarrhalis pathogenicity: review of literature and hospital epidemiology. Laboratory Medicine 2007;38:420-1.

Author

Page authored by Aaron Yeshe, student of Mandy Brosnahan, Instructor at the University of Minnesota-Twin Cities, MICB 3301/3303: Biology of Microorganisms.