Phylogenetic Study of the Genus Campylobacter

Abstract

The phylogenetic relationships of all species in the genus Campylobacter, Wolinella succinogenes, and other gram-negative bacteria were determined by comparison of partial 16S ribosomal ribonucleic acid sequences. The results of this study indicate that species now recognized in the genus Campylobacter make up three separate ribosomal ribonucleic acid sequence homology groups. Homology group I contains the following true Campylobacter species: Campylobacter fetus (type species), Campylobacter coli, Campylobacter jejuni, Campylobacter laridis, Campylobacter hyointestinalis, Campylobacter concisus, Campylobacter mucosalis, Campylobacter sputorum, and “Campylobacter upsaliensis” (CNW strains). “Campylobacter cinaedi,” “Campylobacter fennelliae,” Campylobacter pylori, and W. succinogenes constitute homology group II. Homology group III contains Campylobacter cryaerophila and Campylobacter nitrofigilis. We consider the three homology groups to represent separate genera. However, at present, easily determinable phenotypic characteristics needed to clearly differentiate them are not apparent. The three homology groups are only distantly related to representatives of the alpha, beta, and gamma branches of the purple bacteria, indicating that these bacteria do not belong to any previously defined branch of this phylum.