ABSTRACT
The genus Moraxella belongs to the family Moraxellaceae, which includes the closely related genera Acinetobacter and Psychrobacter. The Moraxella genus itself currently contains 15 different species, including M. lacunata, M. atlantae, M. boevrei, M. bovis, M. canis, M. caprae, M. catarrhalis, M. caviae, M. cuniculi, M. equi, M. lincolnii, M. nonliquefaciens, M. osloensis, M. ovis, and M. saccharolytica.1 Recently, M. pluranimalium has been described as a new species of the genus Moraxella, after its isolation from sheep and pigs.2 Although all of these 15 species have been classiŠed within the genus Moraxella, the classiŠcation of the Moraxellaceae family is still not deŠnitive but continuously evolving. For example, molecular systematic studies (of which 16S ribosomal RNA (rRNA) gene sequencing has long been the “gold standard”) has led to the reclassiŠcation of Riemerella anatipestifer, Psychrobacter phenylpyruvicus, and Oligella urethralis, which were formally known as Moraxella anatipestifer, Moraxella phenylpyruvica, and Moraxella urethralis, respectively.1,3
Of the 15 Moraxella species, M. caprae, M. caviae, M. cuniculi, M. equi, M. lincolnii, M. ovis, M. saccharolytica, M. boevrei, and M. bovis are only associated with diseases in animals, and are thus clinically not relevant. Occasionally, however, some Moraxella species are associated with human disease. SpeciŠcally, M. lacunata has been associated with chronic conjunctivitis, arthritis, and
endocarditis in humans,4-8 while M. nonliquefaciens has been known to cause bacterial infection (botryomycosis) and in³ammation (endophthalmitis).9-11 M. atlantae is an unusual and only rarely isolated species that has been associated with bacteremia in humans,12,13 while M. osloensis rarely causes infections but has been associated with bacteremia and endophthalmitis.14-16 Interestingly, M. canis is an upper-airway commensal bacterium in cats and dogs, and has been considered nonpathogenic for humans even though it has been isolated from humans in a few cases.17,18 The single most important exception to this “Moraxella-animal disease” relationship is M. catarrhalis, an organism that is a strictly human pathogen and that is frequently associated with a range of human disease states.
