Aggregatibacter,Capnocytophaga,Eikenella,Kingella,Pasteurella, and Other Fastidious or Rarely Encountered Gram-Negative Rods

The bacterial genera covered in this chapter are taxonomically diverse—they belong to the families Cardiobacteriaceae, Flavobacteriaceae, Leptotrichiaceae, Neisseriaceae, Pasteurellaceae, and Porphyromonadaceae—but common traits justify their discussion as a group. Most bacteria in this group are part of the microbiota of the nasopharynx and/or the oral cavity of animals and/or humans and are parasitic, with the only environmental genus being Chromobacterium. Transmission from animals occurs by contact (e.g., bites and licking of wounds), from humans to humans by droplets (e.g., directly with Kingella spp. or via human bites with Eikenella corrodens). The epidemiology and clinical significance of the genera Actinobacillus, Aggregatibacter, and Pasteurella, of the family Pasteurellaceae; the genera Cardiobacterium, Eikenella, and Kingella, belonging to the HACEK group; and other less frequently encountered genera are discussed separately. The identification of most genera is difficult by phenotypic methods. Direct microscopy may identify the corresponding bacteria; e.g., the typical morphology of spindle-shaped cells in the Gram stain and the anamnestic history of a dog bite allow the presumptive identification of Capnocytophaga canimorsus. Phenotypic key reactions as well as commercially available systems allow identification of the frequently encountered human isolates. If accurate identification of uncommon isolates is of concern, then molecular methods, e.g., 16S rRNA gene analysis, are necessary. The application of matrix-assisted laser desorption ionization–time-of-flight mass spectrometry shows promising results and is discussed here. Finally, susceptibility testing according to CLSI and EUCAST is described, especially for Pasteurella multocida.