Ar.ca.no.bac.te'ri.um. L. masc. adj. arcanus secret, hidden, secretive; N.L. neut. n. bacterium a small rod; N.L. neut. n. Arcanobacterium secretive bacterium.

Actinobacteria / Actinobacteria / Actinomycetales / Actinomycetaceae / Arcanobacterium

Slender, irregular, bacillary forms predominate during the first 18 h of growth; many cells are arranged at an angle to give V formations. As growth proceeds, cells become granular and segmented so that they resemble small and irregular cocci. Both rods and coccoid cells are Gram-stain-positive, non-acid-fast, and nonmotile; endospores are not formed. Facultatively anaerobic; growth is considerably enhanced in an atmosphere of increased CO₂ tension. Growth is sparse on ordinary media, but enhanced by blood or serum. The optimum temperature for growth is 37°C. Organisms will not withstand heating at 60°C for 15 min. Chemoorganotrophic, having a fermentative type of carbohydrate metabolism. Fermentation end products include acetic and lactic acids; the amount of succinic acid produced may vary from species to species and may even be difficult to detect. Catalase-positive and -negative. Nitrate reduction is usually negative. Characteristic amino acids of the cell-wall peptidoglycan of those species whose peptidoglycan has been examined in detail are based on l-lysine. Other chemotaxonomic properties include rhamnose and glucose as diagnostic whole-cell sugars, lack of mycolic acids, and N-acetylated muramic acid residue of the peptidoglycan and MK-9 (H₄) as the major respiratory quinone.

DNA G + C content (mol%): 50–57.

Type species: Arcanobacterium haemolyticum Collins et al. 1982b, VL10.