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

This chapter covers bacterial genera which are taxonomically diverse and belong to the families Cardiobacteriaceae, Flavobacteriaceae, Fusobacteriaceae, Neisseriaceae, Pasteurellaceae, and Porphyromonadaceae, but common traits justify their discussion as a group. It discusses only species that can be isolated from humans. The Pasteurellaceae consist of several genera, of which four are known to contain human pathogens: Actinobacillus, Aggregatibacter, Haemophilus, and Pasteurella. Phenotypic identification of fastidious gram-negative rods presents several challenges. Triple sugar iron or Kligler's agar may not support the growth of fastidious genera (e.g., Eikenella). Detection of antibodies directed against any of the bacteria discussed in the chapter has been tried on a small scale only and does not seem to offer much value. With specimens normally colonized with aerobic and anaerobic bacteria, as well as with specimens from wounds, e.g., bite wounds, the significance of the bacteria discussed in the chapter depends on their predominance and the absence of other potentially pathogenic bacteria. If these conditions are met, identification to the species level is needed for adequate interpretation and reporting as infectious agents and for susceptibility testing. If none of these conditions is present, a repeat culture and close cooperation between the microbiology laboratory and the physician are necessary for interpretation, for identification to the species or genus level, and for susceptibility testing.