Phylogenetic tree showing the genetic relationship among Helicobacter species on the basis of 16S rRNA sequences. The branch of the “H. felis species group” is shown by the black bar and is marked with a thick arrow. The bracketed strains branch closely in the position designated by the thin arrow. Accession numbers for each of the Helicobacter species are as follows: H. acinonyx, M88148; H. bizzozeronii, V09404; H. canis, L13464; H. cholecystus, U46129; H. cinaedi, M88150; H. felis Cat 1 AF058768; H. felis CS1, M57398; H. felis DS3, M37643; H. felis Dog1, U51870; H. felis Dog2, U51871; H. felis Dog3, U51872; H. fennelliae M88154; “H. heilmannii” 1, L10079; “H. heilmannii” 2, L10080; H. muridarum, M80205; H. mustelae, M35048; H. nemestrinae, X67854; H. pullorum, L36141; H. pylori, M88157; H. salomonis Inkinen, U89351; H. salomonis 6A, V09405; H. trogontum, U65103. The scale (0.1%) indicates percent difference in 16S rRNA sequences.