RANK: Genus

TAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Gammaproteobacteria -> Pseudomonadales -> Moraxellaceae -> Moraxella


Rods or cocci. The rods are often very short and plump, frequently approaching a coccus shape (1.0–1.5 × 1.5–2.5 µm); they usually occur in pairs and short chains (one plane of division). 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 with the adjacent sides flattened (differing planes of division); division in two planes at right angles to each other sometimes results in the formation of tetrads. Gram negative, but often with a tendency to resist Gram decolorization. Flagella are absent. Both rod-shaped and coccal species may be fimbriated. Swimming motility is absent, but surface-bound “twitching motility” has been observed in some rod-shaped species. Aerobic, but some strains may grow weakly under anaerobic conditions. May be encapsulated. Chemoorganotrophic. Most species are nutritionally fastidious and all grow on complex media; some are stimulated significantly by fatty acids (bile salts, Tween 80). Optimum temperature for growth, 33–35°C. Colonies are not pigmented. Oxidase positive (with either tetra- or dimethyl-p-phenylenediamine reagent). Usually catalase positive. No acid is produced from carbohydrates. Usually highly sensitive to penicillin. Parasitic on the mucous membranes of humans and other warm-blooded animals. Strains of the several species of this genus have been shown to be genetically closely related by transformation of the high-level streptomycin resistance marker (Bøvre and Hagen, 1981) as well as by transformation of nutritional markers (Juni et al., 1987, 1988; Juni, 1990). DNA–DNA hybridization studies have shown high relative interspecies binding ratios for DNAs from strains of the genus Moraxella (Tønjum et al., 1989). Species of Moraxella share 95% similarity in their 16S rRNA gene sequences.The mol% G + C of the DNA is: 40.0–47.5 (Tm, Bd, HPLC).Type species: Moraxella lacunata


Antibiotic Resistance
  • Tetracycline (teth)