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- Arcanobacterium haemolyticum: is the major human pathogen in this group. Gram positive facultative anaerobe bacillus, not thought to be part of routine human oral or skin flora. Agent mostly causes pharyngitis or soft tissue infections.
- Organisms are thin, curved and may have rudimentary branching.
- β-hemolytic, need to evaluate when catalase-negative and and no Lancefield group antigens found (which would indicate non-streptococcal origin).
- Growth improved on blood-enriched media, 37ºC with 5-10% CO2.
- Hemolysis best observed on human or horse blood in a CO2-enriched atmosphere. May be overlooked on plates with commensal oral flora.
- Sometimes Gram variable on staining.
- Formerly called Corynebacterium hæmolyticum.
- Based on 16S rRNA sequencing, organism distinguished from Corynebacterium spp.
- Other Arcanobacterium spp. may occasionally cause human infection.
- A. pyogenes: mostly an animal pathogen, but an occasional cause of human infection including soft tissues and other sites. Most often described in rural environs.
- A. bernardiae: non-branching on Gram stain. Rare occurrences described causing bacteremia, musculoskeletal and eye infections.