Moraxella

Moraxella is a genus of gram-negative diplococci, with M. catarrhalis being the most clinically relevant species. M. catarrhalis is part of the normal flora of the upper respiratory tract, but it can cause infection in susceptible individuals. The infection is transmitted through respiratory droplets and can lead to chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)) exacerbations in adults and otitis media in children. Moraxella species are catalase- and oxidase-positive, allowing them to resist damage from reactive oxygen species in the highly oxygenated environment of the respiratory tract.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Classification

Gram negative bacteria classification flowchart

Gram-negative bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview:
Most bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview can be classified according to a lab procedure called Gram staining.
Bacteria with cell walls that have a thin layer of peptidoglycan do not retain the crystal violet stain utilized in Gram staining. These bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview do, however, retain the safranin counterstain and thus appear as pinkish-red on the stain, making them gram negative. These bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview can be further classified according to morphology (diplococci, curved rods, bacilli, and coccobacilli) and their ability to grow in the presence of oxygen (aerobic versus anaerobic). The bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview can be more narrowly identified by growing them on specific media (triple sugar iron (TSI) agar) where their enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body's constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes can be identified (urease, oxidase) and their ability to ferment lactose can be tested.
* Stains poorly on Gram stain
** Pleomorphic rod/coccobacillus
*** Require special transport media

Image by Lecturio.

Characteristics

Features:

  • Stain: gram-negative
  • Morphology: diplococcus
  • Nonmotile
  • Growth and culture:
    • Microaerophilic
    • Oxidase-positive, catalase-positive
  • Asaccharolytic (does not ferment carbohydrates Carbohydrates Carbohydrates are one of the 3 macronutrients, along with fats and proteins, serving as a source of energy to the body. These biomolecules store energy in the form of glycogen and starch, and play a role in defining the cellular structure (e.g., cellulose). Basics of Carbohydrates)

M. catarrhalis and M. lacunata are the most clinically relevant species within this genus.

Moraxella catarrhalis

Moraxella catarrhalis (diplococcus formation)

Image: “Moraxella Catarrhalis” by CDC/Dr. W.A. Clark. License: Public Domain

Pathogenesis

Transmission

  • Humans are the primary reservoir.
  • M. catarrhalis spreads from person to person via respiratory droplets.
  • Nasopharyngeal colonization: 
    • Common in infancy, but declines with age
    • Bacteria can migrate to the middle ear from the nasopharynx via the Eustachian tube.
    • ↑ Rate of colonization noted with increased pneumococcal vaccination Vaccination Vaccination is the administration of a substance to induce the immune system to develop protection against a disease. Unlike passive immunization, which involves the administration of pre-performed antibodies, active immunization constitutes the administration of a vaccine to stimulate the body to produce its own antibodies. Vaccination (which is believed to cause shifts in respiratory microbiome).

Pathogenic features

  • Opportunistic pathogen: 
    • Infection occurs in the setting of a weakened immune system or owing to existing respiratory disease (i.e., chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD))).
    • Bacterial stress (i.e., cold shock Shock Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. Types of Shock response) causes expression of pathogenic mechanisms within M. catarrhalis.
  • Pathogenic mechanisms:
    • Adhesins allow the bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview to bind to the mucosa.
    • Inhibits toll-like receptor 2 signaling (responsible for foreign substance recognition), allowing for immune system evasion
    • Aggregates and creates a biofilm, making it difficult for antibiotics to reach the bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview

Associated Diseases

M. catarrhalis

  • Tracheobronchitis and pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia:
    • Noted in susceptible individuals, most commonly manifesting as acute COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) exacerbations
    • M. catarrhalis causes 10%–20% of COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) exacerbations.
  • Otitis media: M. catarrhalis causes 15%–20% of cases of otitis media in children.  
  • Uncommon cause of acute bacterial sinusitis Sinusitis Sinusitis refers to inflammation of the mucosal lining of the paranasal sinuses. The condition usually occurs concurrently with inflammation of the nasal mucosa (rhinitis), a condition known as rhinosinusitis. Acute sinusitis is due to an upper respiratory infection caused by a viral, bacterial, or fungal agent. Sinusitis

M. lacunata

M. lacunata is a common cause of chronic angular blepharoconjunctivitis in humans.

Diagnosis

  • Clinical features of the diseases are often sufficient in arriving at the diagnosis.
  • Microbiologic studies are often reserved for recurrent, severe conditions or for cases in which therapy has failed.
  • Other tests are determined by clinical presentation (chest X-ray for suspected pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia).

Treatment

  • Moraxella: > 90% produce β-lactamase and thus are resistant to penicillin, ampicillin, and amoxicillin.
  • Susceptible to amoxicillin–clavulanate, macrolides Macrolides Macrolides and ketolides are antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking transpeptidation. These antibiotics have a broad spectrum of antimicrobial activity but are best known for their coverage of atypical microorganisms. Macrolides and Ketolides, extended-spectrum cephalosporins Cephalosporins Cephalosporins are a group of bactericidal beta-lactam antibiotics (similar to penicillins) that exert their effects by preventing bacteria from producing their cell walls, ultimately leading to cell death. Cephalosporins are categorized by generation and all drug names begin with "cef-" or "ceph-." Cephalosporins, tetracyclines Tetracyclines Tetracyclines are a class of broad-spectrum antibiotics indicated for a wide variety of bacterial infections. These medications bind the 30S ribosomal subunit to inhibit protein synthesis of bacteria. Tetracyclines cover gram-positive and gram-negative organisms, as well as atypical bacteria such as chlamydia, mycoplasma, spirochetes, and even protozoa. Tetracyclines, fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones
Community-acquired moraxella catarrhalis

Pneumonia secondary to Moraxella catarrhalis:
Chest X-ray shows a left lower lobe infiltrate secondary to Moraxella catarrhalis, a gram-negative diplococcus that can be an etiologic agent for lung infections in immunocompromised patients and in those with chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)).

Image: “Chest X-ray on admission” by Hospital Universitario Central de Asturias (HUCA), Instituto Nacional de Silicosis (INS), Área del Pulmón, Facultad de Medicina, Universidad de Oviedo, 33005 Oviedo, Spain. License: CC BY 4.0

References

  1. Aebi, C. (2011). Moraxella catarrhalis—pathogen or commensal? Adv Exp Med Biol 697:107–116.
  2. Goldstein, E. J. C., Murphy T. F. (2009). Moraxella catarrhalis: a human respiratory tract pathogen. Clin Infect Dis 000:000–000. https://academic.oup.com/cid/article/49/1/124/371116
  3. Heiniger, N., Troller, R., Meier, P.Ss, Aebi, C. (2005). Cold shock response of the UspA1 outer membrane adhesin of Moraxella catarrhalis. Infect Immun 000:000–000. https://pubmed.ncbi.nlm.nih.gov/16299321/
  4. Murphy, T. F., File, T. M. (2019). Moraxella catarrhalis infections. UpToDate. Retrieved 23 April 2021, from https://www.uptodate.com/contents/moraxella-catarrhalis-infections
  5. Pelton, S., Tahtinen, P., Kaplan, S.L., Isaacson, G.C. (2020). Acute otitis media in children: dpidemiology, microbiology, and complications. UpToDate. Retrieved 23 April 2021, from https://www.uptodate.com/contents/acute-otitis-media-in-children-epidemiology-microbiology-and-complications

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