Moraxella catarrhalis

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.

Moraxella catarrhalis is a human pathogen with an affinity for the human upper respiratory tract and the middle ear. Other primates, such as macaques, might become infected by this bacterium. Rodents including rats, mice, and chinchillas have been used to study Moraxella catarrhalis with varying degrees of success.

The taxonomy of Moraxella catarrhalis is a topic that has caused confusion in the past. The bacteria was initially placed in the genus Neisseria, before being moved into a separate genus named Branhamella in honor of Dr. Sara Branham in 1970. In 1984 this bacterium once again had a change in taxonomy and was moved to the genus Moraxella. Some individuals disagreed with this change, the rationale being 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.

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. The genome was sequenced using a hybrid assembly from two different instrumental methods, Illumina MiSeq and Ion Torrent, and the final assembly produced was composed of 18 contigs. The genome was found to be 1,886,586 bp in length, encoding for 1,736 total genes.

This bacterium has been 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. Current estimates have M. catarrhalis as the cause of approximately 10% of all chronic obstructive pulmonary disease exacerbations, impacting millions of people each year.

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 as 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.