Moraxella

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Moraxella

Scientific classification

Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Gamma Proteobacteria
Order:	Pseudomonadales
Family:	Moraxellaceae
Genus:	Moraxella

Species

M. catarrhalis
M. bovis

Moraxella is a genus of Gram negative bacteria in the Moraxellaceae family. Moraxella catarrhalis is associated with human disease, being linked with respiratory tract infections. In the past, Moraxella catarrhalis, which appears as pairs of cocci and is a gram negative bacterium that morphologically resembles Neisseria by gram stain, was called Neisseria catarrhalis. Unlike Neisseria, which grows on chocolate agar, M. catarrhalis grows on blood agar. (Note that up until ten years ago, M. catarrhalis was called Branhamella catarralis).

M. catarrhalis resides in the human nasopharynx. This bacterium causes similar symptoms to Nontypable Haemophilus Influenza (NTHI), although it is much less virulent than NTHI. M. catarrhalis is the third most common bacterial cause of otitis media and sinusitis after Streptococcus pneumoniae and Haemophilus, respectively. In patients with pre-existing chronic lung disease, tracheobronchitis and pneumonia can ensue. Of further note, Moraxella catarrhalis hardly ever causes bacteremia or meningitis, unlike Neisseria meningitides, which is a morphologic cousin of M. catarrhalis (see above).

The immune response to M. catarrhalis is likely mediated by an antibody to the outer membrane proteins of this organism. Any other immune mechanisms are unknown at this time.

The antibiotic susceptibility of M. catarrhalis is similar to NTHI. The majority of these organisms make beta-lactamase, an enzyme that renders beta lactam antibiotics useless; thus, they are resistant to beta lactams such as penicillin. There currently exists no vaccine to M. catarrhalis, but number of outer membrane proteins are currently being studied for the development of such a vaccine.

The species Moraxella bovis causes keratoconjunctivitis in cattle.