MORAXELLA: CHARACTERISTICS, MORPHOLOGY, SPECIES, PATHOLOGIES - BIOLOGY - 2024

Moraxella is a genus that encompasses bacterial species belonging to the normal microbiota of the nasopharynx and to a lesser extent in the genital tract. Sometimes its members can act as opportunistic pathogens, since some of its species have been isolated as etiological agents of nosocomial infections, infected wounds, pneumonia, systemic infections, among others.

The main species of this genus is Moraxella catarrhalis, which has also been known as Branhamella catarrhalis. This is considered the third most important pathogen in the respiratory tract after Streptococcus pneumoniae and Haemophilus influenzae.

A curious fact is that the prevalence of this bacterium becomes more evident during the autumn and winter seasons.

Among the infections that it generates in humans are: sinusitis, otitis media, pneumonia (especially in the elderly) and other lower respiratory tract infections.

Moraxella canis

It is a bacterium that, like others of the Moraxella genus, is gram negative, catalase and oxidase positive. It is found fundamentally as part of the normal microbiota of the oral cavity of dogs.

This bacterium grows very well on blood agar and chocolate agar. It can be transmitted to humans through a bite or when the dog runs its tongue over a wound on the person. Despite this, very few cases of Moraxella canis infections have been described in humans.

Moraxella bovis

These bacteria have a varied morphology, they can appear as cocci or bacilli. Likewise, they can be found in pairs or short chains and is characterized by presenting a hemolytic factor that produces a dermonecrotoxin, which is considered a pathogenicity factor. Similarly, they are gram negative and also strict aerobes.

Within the field of veterinary medicine, it is a highly studied bacterium, since it directly affects cattle (cows) causing certain infections such as infectious bovine keratitis or conjunctivitis. Flies are believed to be the main vectors for transmitting the bacteria from a sick animal to a healthy one.

Moraxella phenylpyruvica

This species is not usually pathogenic, but sporadic cases of sinusitis, conjunctivitis, septic arthritis, osteomyelitis, peritonitis, bronchitis, meningitis, endocarditis, infection of central venous catheters, and septicemia have been reported.

Moraxella lacunata

It has been isolated from eye infections (conjunctivitis), but it has also been seen to produce keratitis, chronic sinusitis and endocarditis.

Moraxella

It is part of the normal microbiota of the upper respiratory tract of man and is frequently isolated from the nasal cavity.

However, it has been found in blood (septicemia), ocular secretions (endophthalmitis), CSF (meningitis), lower respiratory tract (pneumonia), septic arthritis and other locations.

Moraxella osloensis

It has been found in patients with bacteremia, meningitis, peritonitis, pyomyositis, osteomyelitis, arthritis, endolphthalmitis, urethritis, vaginitis, and diarrhea.

Moraxella atlantae

It has rarely been found in bacteremia.

Moraxella nonliquefaciens

Moraxella nonliquefaciens colonizes the upper respiratory tract in humans and has occasionally been associated with infections such as pneumonia, eye infections, and rhinitis.

Diseases / pathologies

Some species of the genus Moraxella are considered pathogenic for humans, causing certain infections at the respiratory, auditory and ocular level.

It is important to note that, if these infections are not properly treated, bacteremia can be generated in the patient, through which the bacteria can pass into the individual's blood and cause serious damage, such as endocarditis.

Otitis media

It is caused by Moraxella catarrhalis and is seen more often in children than in adults.

Among the most common symptoms are earache and fever. Sometimes there may be fluid drainage through the ear. It is also common to have dizziness and nasal congestion problems.

Sinusitis

It is an infection that occurs at the level of the paranasal sinuses, whose walls are infected by bacteria such as Moraxella catarrhalis. It is quite a painful and annoying condition.

The characteristic symptoms of this pathology include: nasal congestion or obstruction, pain and inflammation in the areas around the eyes, cheeks, nose or forehead. The pain is exacerbated when the person lowers his head. There may also be headache, pressure in the ears, fever and even halitosis (bad breath).

Pneumonia

Pneumonia is an infection that is located at the level of the alveoli and causes them to fill with fluid, which can have purulent characteristics (pus). In people who naturally have a delicate immune system, such as children and the elderly, it can be serious.

The main symptoms of this disease are cough with expectoration, shortness of breath, pain in the chest when breathing or coughing, fever, increased perspiration and chills.

Conjunctivitis

It consists of an infection of the transparent membrane of the eye, the conjunctiva. It is caused mainly by bacterial agents, such as some of the Moraxella genus. It is a very annoying infection that can even interfere with vision.

Conjunctivitis infection. Source: Raimundo Pastor People who suffer from conjunctivitis present itching in the affected eye, a gritty sensation, purulent discharge that can harden and obstruct the opening of the eye and of course, redness and inflammation of the eye.

Sensitivity to antibiotics

Because these species were very sensitive to penicillin, it was not necessary to mount an antibiogram. However, it is known that since 1990 most of the strains, especially of the catarrhalis species, are beta-lactamase producers.

Therefore, it is advisable to mount antimicrobial susceptibility tests. But this work is difficult to do, since the CLSI does not specify cut points for the genus Moraxella, which makes its interpretation difficult.

For this reason, some laboratories use the breakpoints described for Haemophilus influenzae or for non-fastidious bacteria that can grow on unsupplemented Müeller Hinton media, or for non-fermenting Gram negative rods.

Moraxella catarrhalis strains are frequently sensitive to quinolones, amoxicillin-clavulanic acid, cephalosporins, ticarcillin, piperacillin, macrolides, chloramphenicol, and aminoglycosides.

However, strains resistant to tetracycline, erythromycin, fluoroquinolone, macrolides, piperacillin, and some cephalosporins have been reported.

References

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