MORAXELLA

'''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, ''M. catarrhalis'', which appears as pairs of cocci and is a gram negative bacterium that morphologically resembles ''Neisseria'' by Gram stain, was called ''Neisseria catarrhalis''. However, 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 catarrhalis''.)

Contents

Epidemiology and Disease

Host Response

Treatment

References

Epidemiology and Disease

''M. catarrhalis'' resides in the human nasopharynx. This bacterium causes similar symptoms to nontypable–''Haemophilus influenzae'' (NTHI), although it is much less virulent. ''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, ''M. catarrhalis'' hardly ever causes bacteremia or meningitis, unlike ''Neisseria meningitidis'', which is a morphologic cousin of ''M. catarrhalis'' (see above).
The species ''Moraxella bovis'' causes infectious bovine keratoconjunctivitis in cattle.

Host Response

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.

Treatment

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.

References

Lecture notes of Dr. Daniel Musher, Baylor College of Medicine, Houston, Texas