Update on the HACEK group of fastidious gram-negative bacilli, Part I

The HACEK group of bacteria—Haemophilus parainfluenzae, Aggregatibacter species (Aggregatibacter aphrophilus, Aggregatibacter actinomycetemcomitans, and Aggregatibacter segnis), Cardiobacterium species (Cardiobacterium hominis and Cardiobacterium valvarum), Eikenella corrodens, and Kingella species—are fastidious gram-negative bacilli that are found in the human upper respiratory and genitourinary tracts. The HACEK bacteria are particularly associated with bacteremia and endocarditis, along with a variety of other infectious processes. This article describes the taxonomic status of the HACEK group, the types of infections and clinical specimens that may yield such organisms on culture, the phenotypic characteristics that are useful for species identification, and the susceptibility of these organisms to antimicrobial agents used for the treatment of HACEK group infections. Part I of this article will addresses the clinical significance of the HACEK group and specifically addresses Haemophilus, Aggregatibacter, and Cardiobacterium.