Aggregatibacter species


  • Aggregatibacter spp. are normal residents of human oropharyngeal flora (especially dental plaques and gingiva), sometimes urogenital flora.
    • Member of Pasteurellaceae family.
  • Aggregatibacter actinomycetemcomitans (Aa) is a facultative Gram-negative, slowly growing coccobacillus.
    • Formerly known as Actinobacillus actinomycetemcomitans, a member of the HACEK group.
      • Earlier literature called the organism Haemophilus actinomycetemcomitans.
    • Original name due to descriptions of infections with actinomycotic-like presentations.
      • When isolated in an abscess, almost always found in conjunction with Actinomyces spp.
    • Generally easily isolated, but a slow grower and may need > 7d incubation.
    • The most common cause of Aggregatibacter endocarditis.
  • A. aphrophilus: formerly Haemophilus aphrophilus [Fig], is the second most common cause of Aggregatibacter endocarditis.
  • A. paraphrophilus: formerly Haemophilus paraphrophilus, a less common cause of endocarditis of this species (usually mitral valve), may also cause brain abscess.
    • Also found in the GI tract.
  • A. segnis: uncommon commensal in the oropharynx, a rare cause of endocarditis, bacteremia.
  • A. urae: meningitis reported.

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Last updated: April 11, 2024