Moraxella
Encyclopedia
Moraxella is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

 bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 in the Moraxellaceae
Moraxellaceae
The Moraxellaceae are a family of Gammaproteobacteria, including a few pathogenic species. Other are harmless parasites of mammals and humans or occur in water or soil...

 family. It is named after the Swiss ophthalmologist
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...

 Victor Morax
Victor Morax
Victor Morax was a French ophthalmologist who was born in Morges, Switzerland. He studied in Freiburg and Paris, and from 1891 to 1903 he worked at the Pasteur Institute in Paris...

. The organisms are short rods, coccobacilli or, as in the case of Moraxella catarrhalis
Moraxella catarrhalis
Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system and joints of humans.-History:...

, diplococci in morphology, with asaccharolytic, oxidase
Oxidase
An oxidase is any enzyme that catalyzes an oxidation-reduction reaction involving molecular oxygen as the electron acceptor. In these reactions, oxygen is reduced to water or hydrogen peroxide ....

-positive and catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...

-positive properties. Moraxella catarrhalis
Moraxella catarrhalis
Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system and joints of humans.-History:...

 is the clinically most important species under this genus.

Roles in disease

The organisms are commensals of mucosal surfaces and sometimes give rise to opportunistic infection
Opportunistic infection
An opportunistic infection is an infection caused by pathogens, particularly opportunistic pathogens—those that take advantage of certain situations—such as bacterial, viral, fungal or protozoan infections that usually do not cause disease in a healthy host, one with a healthy immune system...

.
  • Moraxella catarrhalis
    Moraxella catarrhalis
    Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system and joints of humans.-History:...

     usually resides in respiratory tract, but can gain access to the lower respiratory tract
    Lower respiratory tract
    The term lower respiratory tract refers to the portions of the respiratory system from the trachea to the lungs.Lower respiratory tract infections can be the cause of several serious illnesses, including pneumonia....

     in patients with chronic chest disease or compromised host defences, thus causing tracheobronchitis and pneumonia
    Pneumonia
    Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...

    . It is also one of the notable causes of otitis media
    Otitis media
    Otitis media is inflammation of the middle ear, or a middle ear infection.It occurs in the area between the tympanic membrane and the inner ear, including a duct known as the eustachian tube. It is one of the two categories of ear inflammation that can underlie what is commonly called an earache,...

     and sinusitis
    Sinusitis
    Sinusitis is inflammation of the paranasal sinuses, which may be due to infection, allergy, or autoimmune issues. Most cases are due to a viral infection and resolve over the course of 10 days...

    . It causes similar symptoms to Haemophilus influenzae
    Haemophilus influenzae
    Haemophilus influenzae, formerly called Pfeiffer's bacillus or Bacillus influenzae, Gram-negative, rod-shaped bacterium first described in 1892 by Richard Pfeiffer during an influenza pandemic. A member of the Pasteurellaceae family, it is generally aerobic, but can grow as a facultative anaerobe. H...

    , although it is much less virulent. Unlike Neisseria meningitidis
    Neisseria meningitidis
    Neisseria meningitidis, often referred to as meningococcus, is a bacterium that can cause meningitis and other forms of meningococcal disease such as meningococcemia, a life threatening sepsis. N. meningitidis is a major cause of morbidity and mortality during childhood in industrialized countries...

    , which is a morphologic cousin of Moraxella catarrhalis, it hardly ever causes bacteremia
    Bacteremia
    Bacteremia is the presence of bacteria in the blood. The blood is normally a sterile environment, so the detection of bacteria in the blood is always abnormal....

     or meningitis
    Meningitis
    Meningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...

    .

  • Moraxella lacunata is one of the causes of blepharoconjunctivitis in human.

  • Moraxella bovis
    Moraxella bovis
    Moraxella bovis is a Gram-negative, aerobic, oxidase-positive diplococcus that is implicated in infectious keratoconjunctivitis in cattle, also colloquially known as Pink Eye.-Weblinks:* - Department of Primary Industries...

     is the cause of Infectious bovine keratoconjunctivitis
    Infectious bovine keratoconjunctivitis
    Infectious bovine keratoconjunctivitis, or IBK, is a veterinary infection of cattle caused by Moraxella bovis, a gram negative, β-haemolytic, aerobic, rod shaped bacterium. It is spread by direct contact or by the common fly serving as a vector. It is the most common ocular disease of cattle...

    ; known colloquially in the United Kingdom as 'New Forest Eye'. As a strict aerobe, M. bovis is confined to the cornea and conjunctiva, resulting in a progressive, non-self-limiting keratitis, ulceration and - ultimately - rupture of the cornea. The disease is relatively common, infecting cattle only. Treatment is via the use of either subconjunctival injection of a Tetracycline, or topical application of Cloxacillin, the former being more effective. The bacterium can be transmitted by flies, so fly control may be necessary on farms throughout the summer. Rupture of the eye is more serious, and requires immediate enucleation, though the procedure itself carries a good prognosis.
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