MICROBIOLOGY

• 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.
    • Implicated in periodontitis and gingivitis.
• A. aphrophilus: formerly Haemophilus aphrophilus [Fig], is the second most common cause of Aggregatibacter endocarditis.
  • Most common in this group to be the cause of a brain abscess.
• 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.