Moraxella

Abstract Mo.ra.xel'la. N.L. dim. fem. n. Moraxella , named after V. Morax, a Swiss ophthalmologist who pioneered the recognition of the type species. Moraxella species are Gram‐negative rods or cocci but often with a tendency to resist decolorization. The rods are often very short and plump, frequently approaching a coccus shape (1.0–1.5 × 1.5–1.5 μm); they usually occur in pairs and short chains. Variation in cell size, shape, and filament or chain formation is often seen in cultures, the pleomorphism being enhanced by lack of oxygen and by incubation temperatures above the optimum. The cocci are usually smaller (0.6–1.0 μm in diameter) and occur as single cells or in pairs; sometimes results in the formation of tetrads. Flagella are absent. Both coccal and rod‐shaped species can be fimbriated. Absence of swimming motility, but surface‐bound “twitching motility” has been observed in some rod‐shaped species. Aerobic, but some species can grow weakly under anaerobic conditions. May be encapsulated. Chemoorganotrophic. Most species are nutritionally fastidious, and all grow in complex media; some are stimulated significantly by fatty acids (bile salts and Tween 80). The optimal temperature for growth is between 33 and 35°C. Colonies are not pigmented. Oxidase‐positive. Usually catalase‐positive. No acid is produced from carbohydrates. Species of this genus share 96–99% similarity in their 16S rRNA gene sequences. The major fatty acids in most species are C 18 :1 ω9 c and C 16:1 ω7 c . The major quinone is Q‐8. Members of the class Gammaproteobacteria and family Moraxellaceae . Parasitic on the mucous membranes of humans and other warm‐blooded animals. DNA G + C content (mol%) : 40–48.1 ( T m , Bd, HPLC). Type species : Moraxella lacunata Lwoff 1939 AL , synonym: “ Bacillus lacunatus ” Eyre 1900. Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the genus Moraxella is: correct name (last update, February 2025) * . LPSN classification: Bacteria / Pseudomonadati / Pseudomonadota / Gammaproteobacteria / Pseudomonadales / Moraxellaceae / Moraxella The genus Moraxella can also be recovered in the Genome Taxonomy Database (GTDB) as g__Moraxella (version v220) ** . GTDB classification: d__Bacteria / p__Pseudomonadota / c__Gammaproteobacteria / o__Pseudomonadales / f__Moraxellaceae / g__Moraxella * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776