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.
Epidemiology
Moraxella 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.
History
Moraxella 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. 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.
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.
Genetics
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.
Clinical significance
These bacteria are known to cause otitis media, 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.
The peak rate of colonization 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).
Moraxella 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. Additionally, it causes bacterial pneumonia, especially in adults with a compromised immune system. 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, sepsis (although this is rare), septic arthritis (which is also a rare occurrence),and acute laryngitis in adults and acute otitis media in children. M. catarrhalis is an opportunistic pulmonary invader, and causes harm especially in patients who have compromised immune systems or any underlying chronic disease.
Link with bacteremia
Moraxella catarrhalis has also been linked with septic arthritis in conjunction with bacteremia. 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).
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. 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.