Moraxella CatarrhalisEdit

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Moraxella catarrhalis is a Gram-negative diplococcus that resides as part of the normal flora of the human upper respiratory tract but can also act as an opportunistic pathogen. It was historically described under the name Branhamella catarrhalis and later reclassified to the genus Moraxella, reflecting advances in bacterial taxonomy. In science and medicine, it is commonly discussed alongside Moraxellaceae and Gram-negative bacteria as a member of the respiratory microbiota that can transition to clinical disease under certain conditions. Branhamella catarrhalis is an older synonym that may appear in historical literature, with modern references typically using the current nomenclature Moraxella catarrhalis.

Clinical relevance centers on its association with common head-and-neck infections and, in vulnerable populations, lower respiratory tract disease. In children, it is a notable cause of acute otitis media, and in adults it is linked to rhinosinusitis. Among older adults and people with chronic lung disease, Moraxella catarrhalis can contribute to bronchitis and pneumonia. The organism is responsible for a portion of community-acquired respiratory infections and is an important consideration in antibiotic selection due to its patterns of antimicrobial resistance. Otitis media and Sinusitis are frequently cited clinical contexts, while pneumonia and bronchitis are recognized but less common manifestations in certain groups.

Taxonomy and morphology - Taxonomic placement: Moraxella catarrhalis belongs to the family Moraxellaceae within the class Gammaproteobacteria. Moraxella is the genus, with catarrhalis as the species; nomenclatural history includes the former designation Branhamella catarrhalis. - Morphology and physiology: It is a small, Gram-negative diplococcus. The organism is typically oxidase-positive and catalase-positive, and it grows on routine laboratory media such as blood agar and chocolate agar under capnophilic conditions. It generally does not grow well on some selective media used for other respiratory pathogens. Laboratory identification often relies on a combination of Gram stain appearance, oxidase testing, and specific biochemical or matrix-assisted methods. In modern clinics, MALDI-TOF mass spectrometry is commonly used for rapid species confirmation. Key virulence-associated features include surface adhesins such as UspA1 and UspA2, as well as other outer membrane components that facilitate adherence to respiratory epithelium and interactions with the host immune system. Biofilm formation is also discussed as a factor in persistence and infection. UspA1 UspA2 biofilms.

Epidemiology and clinical significance - Colonization and transmission: Many adults and children harbor Moraxella catarrhalis in the nasopharynx without symptoms. Transmission occurs via close contact and respiratory droplets, particularly in settings such as households and schools. Colonization is usually asymptomatic but can serve as a reservoir for infection. nasopharynx and colonization are relevant terms here. - Disease associations: Inflammation of the middle ear (otitis media) in children and sinus inflammation (rhinosinusitis) in adults are common clinical contexts. In individuals with chronic lung disease or advanced age, lower respiratory tract involvement such as bronchitis or pneumonia is possible, though less frequent. The organism is generally considered a less virulent respiratory pathogen relative to some other bacteria, but its ability to cause disease increases in the presence of risk factors such as age, immune suppression, smoking, or structural lung disease. otitis media rhinosinusitis bronchitis pneumonia COPD.

Pathogenesis and virulence - Adherence and colonization: Surface proteins, including adhesins such as UspA1 and UspA2, promote binding to respiratory epithelial cells, supporting colonization and persistence in the host. These factors contribute to the transition from benign colonization to invasive or semi-invasive disease under favorable conditions. - Immune interactions: The bacterium interacts with host innate immunity in ways that can modulate local inflammatory responses. Biofilm formation is discussed as a mechanism that may shield bacteria from host defenses and some antimicrobial agents, contributing to chronic infection in susceptible individuals. adhesins biofilms. - Antibiotic resistance mechanisms: A notable feature of many Moraxella catarrhalis isolates is the production of beta-lactamase, which confers resistance to penicillin and some related agents. This pattern shapes empirical therapy choices and highlights the importance of susceptibility testing and local resistance data. beta-lactamase antimicrobial resistance.

Diagnosis and laboratory detection - Clinical suspicion: The diagnosis of Moraxella catarrhalis infection relies on clinical presentation supported by microbiological evidence. In respiratory specimens, the characteristic diplococcal morphology can be observed on Gram stain, and oxidase positivity supports identification. - Laboratory methods: Standard culture on appropriate media, combined with species-level identification through biochemical panels or modern methods like MALDI-TOF mass spectrometry, establishes the diagnosis. Antibiotic susceptibility testing informs treatment, especially given the beta-lactamase production observed in a substantial proportion of isolates. Gram-negative bacteria MALDI-TOF mass spectrometry antibiotic susceptibility testing.

Treatment and antimicrobial resistance - General approach: Because many strains produce beta-lactamase, penicillin-class antibiotics alone may be ineffective for Moraxella catarrhalis infections. Treatment choices typically consider beta-lactamase production and local resistance patterns. - Common regimens: Amoxicillin-clavulanate is frequently used to overcome beta-lactamase–mediated resistance. Cephalosporins (such as second- or third-generation agents) are commonly employed, and macrolides or doxycycline may be alternatives in certain populations, depending on susceptibility data. In cases of penicillin allergy or resistance, respiratory fluoroquinolones may be considered in adults, with caution due to resistance concerns and safety profiles. In all cases, susceptibility testing helps tailor therapy. beta-lactamase antibiotic resistance amoxicillin-clavulanate cephalosporins macrolides.

Prevention and public health considerations - Prevention: There is no widely used vaccine for Moraxella catarrhalis as of the present state of knowledge. Public health measures emphasize general infection control, prudent antibiotic use, and vaccination against other respiratory pathogens to reduce overall burden of respiratory infections. Ongoing research explores vaccine strategies targeting surface adhesins and other virulence factors. vaccines infection control.

See also - Otitis media - Sinusitis - Bronchitis - Pneumonia - Antibiotic resistance - Beta-lactamase - UspA1 - UspA2