Arcanobacterium species

Paul G. Auwaerter, M.D.


  • Arcanobacterium haemolyticum: Agent primarily causes pharyngitis or soft tissue infections.
    • The primary human pathogen in this group.
    • Gram-positive facultative anaerobe bacillus is not considered part of routine human oral or skin flora.
      • Organisms are thin, curved and may have rudimentary branching.
      • β-hemolytic, need to evaluate when catalase-negative and no Lancefield group antigens are found (which would indicate non-streptococcal origin).
        • Growth improved on blood-enriched media [Fig 1], 37ºC with 5-10% CO2.
        • Hemolysis is best observed on human or horse blood in a CO2-enriched atmosphere.
          • Frequently overlooked on plates with commensal oral flora.
      • Sometimes Gram variable on staining.
      • Formerly called Corynebacterium hæmolyticum.
        • Based on 16S rRNA sequencing, an organism was distinguished from Corynebacterium spp.
        • Some investigators believe Arcanobacterium haemolyticum is so closely related that it should be named C pyogenes subsp hominis.
  • Other Arcanobacterium spp. may occasionally cause human infection.
    • A. pyogenes: mostly an animal pathogen as a major cause of mastitis in livestock, but an occasional cause of human infection, including soft tissues and other sites. Most often described in rural environs.
      • Reclassified as Trueperella pyogenes.
    • A. bernardiae: non-branching on Gram stain. Rare occurrences described causing bacteremia, musculoskeletal and eye infections.
      • Reclassified as Trueperella bernardiae.
  • Trueperella bernardiae: previously transferred to the Arcanobcaterium genus but now reclassified. A rare cause of human infection (wound, bloodstream, joint, renal).
    • Considered part of normal skin and oral flora.
    • Also frequently not identified as listed as a Corynebacterium spp.

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Last updated: December 11, 2022