Moraxella catarrhalis

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Moraxella catarrhalis
Scientific classification
M. catarrhalis
Binomial name
Moraxella catarrhalis
(Frosch and Kolle 1896) Henriksen and Bøvre 1968 [1]

Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the infection of the host cell by sticking to the host cell using trimeric autotransporter adhesins.

Aerobic organism

An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment. In contrast, an anaerobic organism (anaerobe) is any organism that does not require oxygen for growth. Some anaerobes react negatively or even die if oxygen is present.

Oxidase test microbiological and biochemical method for identification

The oxidase test is a test used in microbiology to determine if a bacterium produces certain cytochrome c oxidases. It uses disks impregnated with a reagent such as N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) or N,N-dimethyl-p-phenylenediamine (DMPD), which is also a redox indicator. The reagent is a dark-blue to maroon color when oxidized, and colorless when reduced. Oxidase-positive bacteria possess cytochrome oxidase or indophenol oxidase. These both catalyze the transport of electrons from donor compounds (NADH) to electron acceptors . The test reagent, TMPD dihydrochloride acts as an artificial electron donor for the enzyme oxidase. The oxidized reagent forms the colored compound indophenol blue. The cytochrome system is usually only present in aerobic organisms that are capable of using oxygen as the terminal electron acceptor. The end-product of this metabolism is either water or hydrogen peroxide.

A diplococcus is a round bacterium that typically occurs in the form of two joined cells. Examples of gram-negative diplococci are Neisseria spp., Moraxella catarrhalis, and Acinetobacter spp. Examples of gram-positive diplococci are Streptococcus pneumoniae and Enterococcus spp.



M. catarrhalis is a human pathogen with an affinity for the human upper respiratory tract. Other primates, such as macaques, might become infected by this bacterium. [2]


M. catarrhalis was previously placed in a separate genus named Branhamella . The rationale for this was that other members of the genus Moraxella are rod-shaped and rarely caused infections in humans. However, results from DNA hybridization studies and 16S rRNA sequence comparisons were used to justify inclusion of the species M. catarrhalis in the genus Moraxella. [3] As a consequence, the name Moraxella catarrhalis is currently preferred for these bacteria. Nevertheless, some in the medical field continue to call these bacteria Branhamella catarrhalis.

The only species of Branhamella is reclassified to Moraxella catarrhalis.

Moraxella is a genus of Gram-negative bacteria in the Moraxellaceae family. It is named after the Swiss ophthalmologist Victor Morax. The organisms are short rods, coccobacilli, or as in the case of Moraxella catarrhalis, diplococci in morphology, with asaccharolytic, oxidase-positive, and catalase-positive properties. M. catarrhalis is the clinically most important species under this genus.

Bacilli taxon (class) Bacilli, including some rod-shaped (bacilli) and some spherical (cocci) bacteria

Bacilli is a taxonomic class of bacteria that includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens such as Bacillus anthracis. Bacilli are almost exclusively gram-positive bacteria.

Moraxella is named after Victor Morax, a Swiss ophthalmologist who first described this genus of bacteria. Catarrhalis is derived from catarrh, from the Greek meaning "to flow down" (cata- implies down; -rrh implies flow), describing the profuse discharge from eyes and nose typically associated with severe inflammation in colds.

Victor Morax French and Swiss ophthalmologist

Victor Morax was a Swiss ophthalmologist born in Morges, Switzerland.

Catarrh is inflammation of the mucous membranes in one of the airways or cavities of the body, usually with reference to the throat and paranasal sinuses. It can result in a thick exudate of mucus and white blood cells caused by the swelling of the mucous membranes in the head in response to an infection. It is a symptom usually associated with the common cold, pharyngitis, and chesty coughs, but it can also be found in patients with adenoiditis, otitis media, sinusitis or tonsillitis. The phlegm produced by catarrh may either discharge or cause a blockage that may become chronic.

Greek language language spoken in Greece, Cyprus and Southern Albania

Greek is an independent branch of the Indo-European family of languages, native to Greece, Cyprus and other parts of the Eastern Mediterranean and the Black Sea. It has the longest documented history of any living Indo-European language, spanning more than 3000 years of written records. Its writing system has been the Greek alphabet for the major part of its history; other systems, such as Linear B and the Cypriot syllabary, were used previously. The alphabet arose from the Phoenician script and was in turn the basis of the Latin, Cyrillic, Armenian, Coptic, Gothic, and many other writing systems.


The whole genome sequence of M. catarrhalis CCUG 353 type strain was deposited and published in DNA Data Bank of Japan, European Nucleotide Archive, and GenBank in 2016 under the accession number LWAH00000000. [4]

Genome entirety of an organisms hereditary information; genome of organism (encoded by the genomic DNA) is the (biological) information of heredity which is passed from one generation of organism to the next; is transcribed to produce various RNAs

In the fields of molecular biology and genetics, a genome is the genetic material of an organism. It consists of DNA. The genome includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA. The study of the genome is called genomics.

The DNA Data Bank of Japan (DDBJ) is a biological database that collects DNA sequences. It is located at the National Institute of Genetics (NIG) in the Shizuoka prefecture of Japan. It is also a member of the International Nucleotide Sequence Database Collaboration or INSDC. It exchanges its data with European Molecular Biology Laboratory at the European Bioinformatics Institute and with GenBank at the National Center for Biotechnology Information on a daily basis. Thus these three databanks contain the same data at any given time.

European Nucleotide Archive Online database from the EBI on Nucleotides

The European Nucleotide Archive (ENA) is a repository providing free and unrestricted access to annotated DNA and RNA sequences. It also stores complementary information such as experimental procedures, details of sequence assembly and other metadata related to sequencing projects. The archive is composed of three main databases: the Sequence Read Archive, the Trace Archive and the EMBL Nucleotide Sequence Database. The ENA is produced and maintained by the European Bioinformatics Institute and is a member of the International Nucleotide Sequence Database Collaboration (INSDC) along with the DNA Data Bank of Japan and GenBank.

Clinical significance

These bacteria are known to cause otitis media, [5] [6] bronchitis, sinusitis, and laryngitis. Elderly patients and long-term heavy smokers with chronic obstructive pulmonary disease should be aware that M. catarrhalis is associated with bronchopneumonia, as well as exacerbations of existing chronic obstructive pulmonary disease.

Otitis media otitis which involves inflammation of the middle ear

Otitis media is a group of inflammatory diseases of the middle ear. The two main types are acute otitis media (AOM) and otitis media with effusion (OME). AOM is an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, increased crying, and poor sleep. Decreased eating and a fever may also be present. OME is typically not associated with symptoms. Occasionally a feeling of fullness is described. It is defined as the presence of non-infectious fluid in the middle ear for more than three months. Chronic suppurative otitis media (CSOM) is middle ear inflammation of greater than two weeks that results in episodes of discharge from the ear. It may be a complication of acute otitis media. Pain is rarely present. All three may be associated with hearing loss. The hearing loss in OME, due to its chronic nature, may affect a child's ability to learn.

Bronchitis type of lower respiratory disease

Bronchitis is inflammation of the bronchi in the lungs. Symptoms include coughing up mucus, wheezing, shortness of breath, and chest discomfort. Bronchitis is divided into two types: acute and chronic. Acute bronchitis is also known as a chest cold.

Sinusitis human disease

Sinusitis, also known as a sinus infection or rhinosinusitis, is inflammation of the mucous membrane that lines the sinuses resulting in symptoms. Common symptoms include thick nasal mucus, a plugged nose, and facial pain. Other signs and symptoms may include fever, headaches, poor sense of smell, sore throat, and cough. The cough is often worse at night. Serious complications are rare. It is defined as acute sinusitis if it lasts less than 4 weeks, and as chronic sinusitis if it lasts for more than 12 weeks.

The peak rate of colonisation by M. catarrhalis appears to occur around 2 years of age, with a striking difference in colonization rates between children and adults (very high to very low).

M. catarrhalis has recently been gaining attention as an emerging human pathogen. It has been identified as an important cause in bronchopulmonary infection, causing infection through pulmonary aspiration in the upper pulmonary tract. [7] Additionally, it causes bacterial pneumonia, especially in adults with a compromised immune system. [8] It has also been known to cause infective exacerbations in adults with chronic lung disease, and it is an important cause in acute sinusitis, maxillary sinusitis, bacteremia, meningitis, conjunctivitis, acute purulent irritation of chronic bronchitis, urethritis, septicemia (although this is rare), septic arthritis (which is also a rare occurrence),and acute laryngitis in adults and acute otitis media in children. [9] [10] M. catarrhalis is an opportunistic pulmonary invader, and causes harm especially in patients who have compromised immune systems or any underlying chronic disease. [7] [9]

M. catarrhalis has also been linked with septic arthritis in conjunction with bacteremia. [9] Although cases of bacteremia caused by M. catarrhalis have been reported before, this was the first instance in which bacteremia caused by M. catarrhalis was also associated with septic arthritis. A microbiological evaluation of the patient (a 41-year-old male) revealed that M. catarrhalis was the cause of the disease rather than Neisseria as was previously believed. This was also the second case of M. catarrhalis causing septic arthritis (although in the first case, no mention of bacteremia was made). [9]

Along with its relation to septic arthritis, bacteremia is also caused by M. catarrhalis infection, which can range in severity from a slight fever to lethal sepsis and an associated respiratory tract infection is usually also identified. [11] Bacteremia infections caused by M. catarrhalis have a 21% mortality rate among patients. However, this may have been due to a lack of knowledge about the bacterium because of its recent recognition as a pathogen. [11]

Infection of high-grade bacteremia was linked with the development of endocarditis. [11] However, the patients without endocarditis has been related to the background of each patient, especially the existence of other illnesses and any possible immune impairments they may have. Also, although bacteremia caused by M. catarrhalis has been infrequently reported, this may be due to a misdiagnosis or oversight because M. catarrhalis was only recently (1990s) identified as an important pathogen. [11] Many chronic diseases in patients with M. catarrhalis bacteremia can be linked to the patients with immune defects or respiratory debility. Likewise, respiratory debility in patients with bacteremic pneumonia caused by M. catarrhalis infection can be linked with increased rates of pharyngeal colonization, enhancement of bacterial adherence to abnormal epithelium, and increased susceptibility of pulmonary parenchyma to infection. [11]

Antibiotic resistance

Antibiotic sensitivity test: This strain shows resistance to ampicillin because it produces the enzyme b-lactamase. This is confirmed by the disc (nitrocefin) labelled b turning red. M. cat BSAC.JPG
Antibiotic sensitivity test: This strain shows resistance to ampicillin because it produces the enzyme β-lactamase. This is confirmed by the disc (nitrocefin) labelled β turning red.

M. catarrhalis can be treated with antibiotics, but it is commonly resistant to penicillin, ampicillin, and amoxicillin. [11]

Current research priorities involve trying to find a suitable vaccine [12] for this genotypically diverse organism, as well as determining factors involved with virulence, e.g. complement resistance. Lipooligosaccharide is considered one possible virulence factor. [12]

Since the recent recognition of M. catarrhalis as an important pathogenic microbe, development of a possible antibiotic has been ongoing. A fraction of M. catarrhalis strains seemed to be resistant to ampicillin, which makes ampicillin and amoxicillin inappropriate choices of antibiotic against it. [7] Although all strains of M. catarrhalis were susceptible to cotrimoxazole, erythromycin, sulfadimidine, and tetracycline, they were also resistant to trimethoprim. [7] M. catarrhalis resistance to beta-lactam antibiotics, such as ampicillin and amoxicillin, is mediated by periplasmic lipoprotein beta-lactamases BRO-1 and BRO-2, which protect the peptidoglycan layer by hydrolyzing the beta-lactam molecules that enter the bacterial cell. [13] The beta-lactamases are produced in the cytoplasm and translocated to the periplasmic space by twin-arginine translocation pathway, which is a protein secretion pathway that transports proteins across a bilipid membrane in a folded state. [14] M. catarrhalis produces and secretes beta-lactamase containing outer-membrane vesicles that can function as an extracellular delivery system of beta-lactam resistance that promotes the survival of otherwise beta-lactam sensitive bacteria in the vicinity of M. catarrhalis. This behavior is beneficial for the other bacteria and can make the antibiotic treatment of polymicrobial infections more difficult. [15] Also, the resistance of M. catarrhalis to other antibiotics may be attributed to beta-lactamase, as well, because the use of these antibiotics has triggered an increase in development of beta-lactamase, which resists antibiotics. [7]

However, a 1994 study has identified a large protein on the surface of M. catarrhalis that may serve as a target for protective antibodies. [8] This UspA (the designated antigen) protein is the first surface-exposed protein on M. catarrhalis that can be a target for biologically active antibodies, and therefore lead to a vaccination. This protein was also present in all of the strains tested. The large size of the exposed protein macromolecule makes it similar to Neisseria gonorrhoeae outer membrane protein macromolecular complex, which implies that UspA may be a single polypeptide chain. [8]

Active immunization, in a study, of M. catarrhalis in the respiratory tract allowed the control of the growth of M. catarrhalis and led to the development of serum antigens. [10] Also, an enhanced ability exists in the test subjects (mice) to clear M. catarrhalis from their lungs. Likewise, passive immunization of M. catarrhalis from the mice respiratory tracts also enhanced the mice's ability to clear the microbes from their lungs, which means that serum antibodies likely play a large role in the immunization and protection of the respiratory tract. [10] Along with outer membrane proteins that are consistent among different strains of M. catarrhalis, a sort of subclass-specific IgG antibody response to certain outer membrane proteins may also exist. Therefore, the outer membrane antigens of M. catarrhalis also provide a possible vaccine source. Also, a bactericidal serum antibody has also been developed in response to the diseases caused by M. catarrhalis. [10]


Treatment options include antibiotic therapy or a so-called "watchful waiting" approach. The great majority of clinical isolates of this organism produce beta-lactamases, so are resistant to penicillin. Resistance to trimethoprim, trimethoprim-sulfamethoxazole (TMP-SMX), clindamycin, and tetracycline have been reported. It is susceptible to fluoroquinolones, most second- and third-generation cephalosporins, erythromycin, and amoxicillin-clavulanate.

Vaccine development

Currently, no vaccine is known in the US against M. catarrhalis infection. It is a significant cause of respiratory tract infections against which a vaccine is sought. Several outer membrane proteins are currently under investigation as potential vaccine antigens, including the porin M35.


During the first reported case of M. catarrhalis causing bacteremia that was associated with septic arthritis, the microbe was cultured, which revealed much about the morphology of its colonies, as well as M. catarrhalis itself. [9] M. catarrhalis is a large, kidney-shaped, Gram-negative diplococcus. It can be cultured on blood and chocolate agar plates after an aerobic incubation at 37 °C for 24 hours. Cultures revealed gray-white hemispheric colonies about 1 mm in diameter. These colonies were fragile and easy to crumble, and appeared to have a waxy surface. [9]

The hockey puck test was applied to these M. catarrhalis colonies, [9] in which a wooden stick is used to try to push the colonies across the plate. The M. catarrhalis colonies scored positively on this test, which means they could be slid across the plate. The colonies did not demonstrate hemolysis, and were not able to ferment glucose, sucrose, maltose, or lactose. They were able to produce DNase. Cultures of the M. catarrhalis tested positive for oxidase and nitrate reduction, which is characteristic of M. catarrhalis. [9] Many laboratories also perform a butyrate esterase test and a beta-lactamase test. Both tests should be positive and can help to rapidly identify it from a culture. [16]

The recognition of M. catarrhalis as a pathogen has led to studies for possible antibodies against it, which have led to a wider understanding of its composition. The outer membrane protein (OMP) profiles of different strains of M. catarrhalis are extremely similar to each other. [8] Analyses of these OMP profiles with monoclonal antibodies (MAbs) revealed that a few proteins with similar molecular masses in the different strains have cross-reactive epitopes. [8] Also, a surface-exposed protein on M. catarrhalis has an unusually high molecular mass. An 80-kDa OMP on M. catarrhalis is immunogenic and common to all nonencapsulated strands of M. catarrhalis, which suggests it may be used as an antigen for immunization. [8]

Protein secretion

M. catarrhalis utilizes the twin-arginine translocation pathway (TAT pathway) for the transport of folded proteins across the inner membrane. [14] The translocase apparatus is a typical Gram-negative TAT translocase consisting of three essential membrane proteins: TatA, TatB and TatC. TatA proteins form a pore through which passenger proteins are transported and TatB and TatC proteins recognize, bind and direct the passenger proteins to the membrane spanning TatA pore. [14] [17]

The M. catarrhalis TAT translocase protein encoding genes tatA, tatB and tatC are located in a single tatABC locus in the bacterial chromosome and are likely to be transcriptionally and translationally linked due to a single-nucleotide overlap between each gene. [14]

Multiple M. catarrhalis proteins have been predicted or tested to contain the highly conserved leader motif for translocation and to be transported by the TAT pathway. Beta-lactamases BRO-1 and BRO-2 have been shown to be transported by the TAT pathway. Other potential passenger proteins include an iron-dependent peroxidase -like protein, a cytochrome c -like protein and a phosphate ABC transporter inner membrane protein- like protein. A functioning TAT pathway is necessary for the optimal growth of M. catarrhalis even in conditions without antibiotics. [14]

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