Infectious Disease and Microbiology – Moraxella (Branhamella) Species

Overview

Moraxella species are aerobic Gram-negative coccobacilli that commonly colonize the human upper respiratory tract and can cause a variety of infections. The most clinically important species is Moraxella catarrhalis, formerly called Branhamella catarrhalis.

These organisms are especially associated with otitis media, sinusitis, bronchitis, and pneumonia, and they may also cause conjunctivitis, bacteremia, endocarditis, and arthritis.

Classification

Genus: Moraxella

Important species:

• M. atlantae

• M. catarrhalis

• M. lacunata

• M. nonliquefaciens

• M. osloensis

• M. phenylpyruvica

Type: Aerobic Gram-negative coccobacillus

Historical Name

Moraxella catarrhalis was historically classified as:

Branhamella catarrhalis

Older literature may therefore refer to the organism as:

Branhamella

Microbiologic Characteristics

Moraxella species are generally:

• Aerobic

• Gram-negative

• Coccobacillary in appearance

• Part of the normal respiratory/oral flora

M. catarrhalis is often described microscopically as a Gram-negative diplococcus, which can resemble Neisseria species.

Incubation Period

The incubation period is:

Unknown

Because many Moraxella infections arise from organisms already colonizing the upper respiratory tract, there is usually no clearly defined incubation period.

Epidemiology

M. catarrhalis is a:

Common human respiratory pathogen

Moraxella species may also exist as normal flora of the:

• Oropharynx

• Upper respiratory tract

• Oral cavity

Colonization is particularly common in children.

Major Risk Groups

Clinically significant disease occurs commonly in:

• Young children

• Older adults

• Patients with chronic pulmonary disease

• Patients with COPD

• Immunocompromised individuals

M. catarrhalis is particularly important in respiratory exacerbations among patients with chronic lung disease.

Otitis Media

M. catarrhalis is an important cause of:

Acute otitis media

especially in children.

It is one of the classic bacterial causes together with:

• Streptococcus pneumoniae

• Nontypeable Haemophilus influenzae

• Moraxella catarrhalis

High-Yield Otitis Pattern

Child with acute otitis media

→ Think of:

S. pneumoniae

• ●

H. influenzae

• ●

M. catarrhalis

Sinusitis

M. catarrhalis is also a recognized cause of:

Acute bacterial sinusitis

particularly in children.

Clinical manifestations can include:

• Nasal congestion

• Purulent nasal discharge

• Facial pain or pressure

• Fever

Lower Respiratory Tract Infection

Moraxella, particularly M. catarrhalis, can cause:

• Acute bronchitis

• COPD exacerbations

• Pneumonia

• Bronchopneumonia

COPD Association

One of the most important adult associations is:

Acute exacerbation of chronic obstructive pulmonary disease

M. catarrhalis commonly infects or colonizes the respiratory tract of older adults with chronic lung disease.

High-Yield COPD Pattern

Older patient with COPD

• ●

Increased cough

• ●

Purulent sputum

• ●

Respiratory exacerbation

→ Consider Moraxella catarrhalis

Laryngitis

The source also lists:

Laryngitis

among upper respiratory tract infections that may be associated with Moraxella species.

Ocular Infections

Neonatal Conjunctivitis

The source describes:

Neonatal conjunctivitis

usually associated with:

M. catarrhalis

Blepharoconjunctivitis

Several Moraxella species can cause:

Blepharoconjunctivitis

The species classically associated with this manifestation is:

Moraxella lacunata

High-Yield Eye Association

M. lacunata

→ Blepharoconjunctivitis

Invasive Disease

Although less common than respiratory disease, Moraxella species can occasionally cause:

• Bacteremia

• Endocarditis

• Septic arthritis

These manifestations are more likely in patients with significant comorbid illness or impaired immunity.

Diagnosis

The primary diagnostic method is:

Culture

Clinical specimens may include:

• Respiratory secretions

• Blood

• Conjunctival material

• Synovial fluid

Species identification can help establish the significance of unusual isolates.

Laboratory Characteristics of M. catarrhalis

M. catarrhalis is typically:

• Gram-negative

• Diplococcal/coccobacillary

• Oxidase positive

• Catalase positive

It can resemble Neisseria microscopically but has distinct biochemical characteristics.

Beta-Lactamase Production

A major therapeutic feature is that:

M. catarrhalis frequently produces beta-lactamase

This means that simple:

Ampicillin

or

Amoxicillin alone

may be ineffective.

High-Yield Resistance Pattern

Moraxella catarrhalis

• ●

Beta-lactamase production

→ Avoid relying on plain amoxicillin when resistance is suspected

→ Amoxicillin–clavulanate provides beta-lactamase protection

Treatment

The source lists:

Amoxicillin–clavulanate

as first-line treatment.

This is a logical choice because clavulanate inhibits many beta-lactamases produced by M. catarrhalis.

Additional Treatment Options

The source also lists:

• Macrolides

• Fluoroquinolones

• Second-generation cephalosporins

• Trimethoprim–sulfamethoxazole

Treatment should be chosen according to:

• Site of infection

• Severity

• Local resistance patterns

• Patient allergies

• Susceptibility results when available

Treatment Principle

Suspected M. catarrhalis infection

• ●

Frequent beta-lactamase production

↓

Choose an agent stable to or protected from beta-lactamase

Examples:

Amoxicillin–clavulanate

or another active alternative

Moraxella catarrhalis vs. Haemophilus influenzae

M. catarrhalis

→ Gram-negative diplococcus/coccobacillus

→ Otitis media

→ Sinusitis

→ COPD exacerbation

→ Frequent beta-lactamase production

Nontypeable H. influenzae

→ Small Gram-negative coccobacillus

→ Otitis media

→ Sinusitis

→ COPD exacerbation

→ Also commonly produces beta-lactamase

Both are major respiratory pathogens.

Moraxella catarrhalis vs. Neisseria

Moraxella catarrhalis

→ Gram-negative diplococcus

→ Respiratory tract pathogen

→ Otitis, sinusitis, COPD exacerbation

→ Usually noninvasive

Neisseria meningitidis

→ Gram-negative diplococcus

→ Meningitis

→ Meningococcemia

Neisseria gonorrhoeae

→ Gram-negative diplococcus

→ Gonorrhea

→ Pelvic inflammatory disease

→ Neonatal conjunctivitis

High-Yield Clinical Pattern

Child with otitis media or sinusitis

or

Older patient with COPD exacerbation

• ●

Gram-negative diplococcus/coccobacillus

• ●

Frequent beta-lactamase production

→ Think Moraxella catarrhalis

Exam Essentials

Genus: Moraxella

Former genus/name: Branhamella

Major species: M. catarrhalis

Type: Aerobic Gram-negative coccobacillus/diplococcus

Normal habitat: Upper respiratory/oral flora

Major infections: Otitis media, sinusitis, bronchitis, COPD exacerbation, pneumonia

Eye association: M. lacunata → blepharoconjunctivitis

Other infections: Bacteremia, endocarditis, arthritis

Diagnosis: Culture

Important resistance mechanism: Beta-lactamase production

Source treatment: Amoxicillin–clavulanate

Alternatives: Macrolide, fluoroquinolone, second-generation cephalosporin, TMP-SMX

Key clinical pearl: Moraxella catarrhalis is a common respiratory pathogen, especially in children with otitis/sinusitis and adults with COPD exacerbations. Because it frequently produces beta-lactamase, amoxicillin–clavulanate is a classic treatment choice.