Branhamella CatarrhalisEdit

Moraxella catarrhalis, historically referred to as Branhamella catarrhalis, is a Gram-negative diplococcus that commonly resides in the human upper respiratory tract as part of the normal microbiota but can also act as a pathogen in a number of clinical contexts. It is one of several organisms capable of causing acute and chronic respiratory infections, particularly in children and in people with preexisting lung conditions. In medical microbiology, the organism is frequently discussed in relation to its propensity to produce beta-lactamase, which has implications for antibiotic choice and clinical management beta-lactamase.

In everyday clinical practice, Moraxella catarrhalis is encountered as part of the broader picture of community-acquired respiratory infections. It is often identified in patients with acute otitis media, sinusitis, or lower-respiratory infections, and it can contribute to exacerbations of chronic obstructive pulmonary disease Chronic obstructive pulmonary disease in susceptible individuals. The organism’s role as both a commensal and an opportunistic pathogen makes understanding its biology and treatment important for clinicians, researchers, and public health professionals managing respiratory illness and antibiotic resistance otitis media sinusitis.

Historically, the bacterium was described under the name Branhamella catarrhalis, but taxonomic revisions led to its current designation as Moraxella catarrhalis. This reclassification reflects refinements in the understanding of the phylogenetic relationships within the Moraxellaceae family and the genus Moraxella, which encompasses several other clinically relevant species. Readers encountering older literature should recognize Branhamella catarrhalis as the same organism now referred to as Moraxella catarrhalis, and the two names are often encountered in parallel in reviews and textbooks Branhamella catarrhalis Moraxella catarrhalis Moraxella.

Taxonomy and nomenclature

Moraxella catarrhalis is a member of the family Moraxellaceae within the order Neisseriales. It is related to other Moraxella species that inhabit the human nasopharynx and respiratory tract, including Moraxella lacunata Moraxella.
The organism is best described as a Gram-negative diplococcus, a characteristic feature visible with standard Gram staining and consistent with other diplococcal pathogens. See also Diplococcus.
In many strains, Moraxella catarrhalis is a beta-lactamase producer, a trait with direct relevance to antimicrobial therapy and resistance patterns beta-lactamase.

Morphology and physiology

Moraxella catarrhalis appears as oxidase-positive, nonmotile Gram-negative diplococci on appropriate culture media. The oxidase reaction is a standard diagnostic clue used in bacteriology workflows oxidase test.
The organism is nonfermentative for carbohydrates (asaccharolytic) and tends to grow well on enriched media such as chocolate agar, with characteristic colony features that clinicians may be able to recognize alongside other diagnostic cues Gram-negative bacteria.
A notable clinical feature is its frequent production of beta-lactamase, which underpins certain patterns of antibiotic resistance and informs empiric therapy decisions in respiratory infections beta-lactamase.

Epidemiology

Moraxella catarrhalis is a common inhabitant of the upper respiratory tract in humans and participates in the normal nasopharyngeal flora. Carriage rates vary by age, geography, and sampling method, with higher carriage in children and in settings with close contact nasopharynx.
Illness caused by Moraxella catarrhalis often presents in the setting of a preceding viral upper respiratory infection or coexisting airway disease, and it can contribute to both upper and lower respiratory tract infections. In particular, it is a well-recognized cause of acute otitis media in children and sinusitis in both adults and children, and it can participate in COPD-related exacerbations otitis media sinusitis Chronic obstructive pulmonary disease.

Clinical disease

Otitis media: Moraxella catarrhalis is among the several bacterial culprits of acute otitis media in children, frequently detected in middle-ear fluid in conjunction with clinical symptoms. Its role is typically considered alongside Streptococcus pneumoniae and non-typeable Haemophilus influenzae, with antibiotics chosen to cover the common pathogens in pediatric acute otitis media otitis media.
Sinusitis: Infections of the maxillary and other paranasal sinuses may involve Moraxella catarrhalis, either as a primary pathogen or as part of polymicrobial sinus infections. Management often parallels approaches used for other common bacterial sinusitis pathogens sinusitis.
Pneumonia and COPD: Moraxella catarrhalis can be isolated from cases of community-acquired pneumonia, particularly in older adults or those with underlying lung disease. It can also participate in respiratory tract infections in patients with COPD, where it may contribute to sputum production and symptom burden amid complex airway inflammation pneumonia Chronic obstructive pulmonary disease.
Rare or opportunistic infections: While most cases arise from colonization and typical respiratory infections, Moraxella catarrhalis can cause invasive disease in individuals with substantial immunosuppression or co-morbid conditions, including meningitis or bacteremia in rare circumstances. These instances are far less common than the more routine mucosal infections described above bacteremia.

Diagnosis

Diagnostic workup typically includes culture of respiratory specimens (ear discharge, sinus aspirate, sputum) on enriched media. Microscopic examination showing Gram-negative diplococci and an oxidase-positive result supports a Moraxella catarrhalis identification in the appropriate clinical context Gram-negative bacteria oxidase test.
Modern laboratories often employ MALDI-TOF mass spectrometry for rapid confirmation, supplemented by targeted molecular assays or sequencing when necessary. PCR-based detection and sequencing can be used to confirm species identity in challenging cases MALDI-TOF.
Antibiotic susceptibility testing is important due to the organism’s beta-lactamase production. Many strains display resistance to penicillins unless a beta-lactamase inhibitor is included or a broader-spectrum cephalosporin is used. Clinicians frequently rely on local antibiograms to guide therapy beta-lactamase.

Treatment and antibiotic resistance

Given the beta-lactamase activity of a substantial subset of Moraxella catarrhalis isolates, penicillin monotherapy is often ineffective for infections caused by these strains. Appropriate empiric therapy frequently includes a beta-lactam/beta-lactamase inhibitor combination (for example, amoxicillin-clavulanate) or a cephalosporin with adequate activity against Moraxella species amoxicillin-clavulanate beta-lactam antibiotics.
Macrolide and doxycycline use may be considered in some settings, but resistance patterns vary by region and patient population. Decision-making should be guided by local resistance data and patient allergies or contraindications macrolide.
Antibiotic stewardship remains important in managing Moraxella catarrhalis infections, balancing effective treatment with the broader goal of reducing antimicrobial resistance in the community antibiotic resistance.

Public health and research context

Moraxella catarrhalis continues to be studied in the context of upper respiratory tract colonization, otitis media, and COPD management. Research efforts focus on pathogenesis, treatment optimization, vaccine development, and the organism’s role in multi-pathogen respiratory infections. While vaccines against Moraxella catarrhalis have not yet become standard practice, vaccine research and immunological studies are ongoing to reduce the burden of associated diseases Otitis media respiratory tract infection.
The organism’s natural history as a colonizer and pathogen informs public health strategies around vaccination, antibiotic stewardship, and strategies to prevent secondary infections following viral illnesses nasopharynx.